/ 


HUBERT  DYER. 


A  SYSTEMATIC  HANDBOOK 

OF 

VOLUMETRIC   ANALYSIS, 


V\  6  R  A  R  y 
OF  THE 


SYSTEMATIC     HANDBOOK 


OP 


VOLUMETRIC   ANALYSIS; 


OR, 


THE    QUANTITATIVE    ESTIMATION 

OF  CHEMICAL    SUBSTANCES   BY  MEASURE,   APPLIED  TO 
LIQUIDS,   SOLIDS,  AND   GASES, 


ADAPTED   TO   THE   REQUIREMENTS  OF  PURE   CHEMICAL   RESEARCH, 
PATHOLOGICAL    CHEMISTRY,    PHARMACY,    METALLURGY,    MANUFACTURING 

CHEMISTRY,   PHOTOGRAPHY,   ETC.,   AND  FOR  THE  VALUATION 
OF   SUBSTANCES  USED   IN   COMMERCE,   AGRICULTURE,  AND   THE  ARTS. 


BY 

FRANCIS   BUTTON,   F.I.C.,   F.C.S., 

|) 

PUBLIC  ANALYST  FOR  THE  COUNTY  OF  NORFOLK  ; 

LATE   MEMBER   OF   COUNCIL  OF  THE   SOCIETY   OF   PUBLIC  ANALYSTS  ; 

LATE   MEMBER   OF   COUNCIL  OF  THE   PHARMACEUTICAL  SOCIETY  OF   GREAT   BRITAIN; 

CORRESPONDING   MEMBER  OF  THE   IMPERIAL  PHARMACEUTICAL  SOC.  OF   ST.  PETERSBURGH 

CORRESPONDING   MEMBER  OF  THE  AUSTRIAN  APOTHEKER  VEREIN,   VIENNA; 

CONSULTING  CHEMIST  TO  THE   NORFOLK  CHAMBER   OF   AGRICULTURE; 

ETC.,   ETC. 


SIXTH    EDITION,    FNU^iEfl 


PHILADELPHIA  : 

P.    BLAKISTON,    SON,    &    CO., 

1012  WALNUT  STREET. 

1890. 


[All  rights  reserved.] 


PREFACE. 


THE  fifth  edition  of  this  book,  and  the  largest  yet  issued, 
having  been  absorbed  in  a  shorter  space  of  time  than  any 
former  edition,  is  an  evidence  of  the  increasing  demand 
for  volumetric  methods  of  analysis,  and  due,  most  likely, 
to  the  necessity  for  shorter  technical  methods  in  connexion 
with  manufacturing  processes  of  various  kinds. 

The  present  book  is  enlarged  by  about  fifty  pages  of  new 
matter,  with  twelve  new  illustrations,  comprising  fuller 
descriptions  of  the  indicators  used  in  saturation  analyses 
and  additions  to  methods  of  titration  in  almost  every 
section.  There  is  also  added  a  table  of  co-efficients  and 
logarithms  for  use  in  volumetric  analyses,  taken  partly 
from  some  of  the  earlier  editions  of  Mohr's  Titrirmethode, 
from  Dr.  W.  H.  Ince's  tables  published  in  the  Analyst, 
and  from  Mr.  A.  E.  Johnson's  valuable  Analyst's 
Laboratory  Companion,  issued  by  Messrs.  J.  &  A.  Churchill. 

Professor  McLeod  has  kindly  furnished  me  with  revised 
and  corrected  tables  of  logarithms  required  in  the  analysis 
of  gases  supplementary  to  his  original  article,  and  which 
are  now  inserted  at  the  end  of  the  book,  as  was  the  case  in 
the  second  edition.  I  shall  be  happy  to  supply  separate 

331983 


VI  PREFACE. 

copies  of  these  tables  for  laboratory  use,  and  also  those 
required  for  Frankland's  and  Armstrong's  method  of 
water  analysis,  to  any  one  who  desires  them,  on  receipt  of 
address. 

I  am  indebted  to  Mr.  J.  Lunt,  B.Sc.,  for  a  condensed 
report  on  Schiitzenberger's  method  of  estimating  oxygen 
in  waters,  etc.,  worked  out  by  Sir  Henry  Eoscoe  and 
himself,  as  shown  in  §  68.  Professor  P.  P.  Bedson  has 
also  kindly  sent  me  photographs  of  his  modified  gas 
pipettes  (see  fig.  94) ;  and  last,  but  not  least,  I  am 
indebted  to  my  friend  Mr.  W.  Thorp,  B.Sc.,  for  his  kind 
supervision  of  the  proof  sheets,  and  for  valuable  suggestions 
throughout  the  entire  book. 

FKANCIS   SUTTON. 

NORWICH, 

October,  1890. 


CONTENTS. 


PART   I. 

Sect.  Page 

1.  General  Principles             .                .                .                .  .1 

2.  The  Balance               .                .                .                .                .  5 

3.  Volumetric  Analysis  without  "Weights          ;  .                .  .5 

4.  Volumetric  Analysis  without  Burettes    ...  6 

5.  The  Burette       .               .                .                .               .  .6 

6.  The  Pipette               .....  14 

7.  The  Measuring  Flasks       .                .                .                .  .15 

8.  The  Correct  Reading  of  Graduated  Instruments     .                .  16 

9.  The  Weights  and  Measures  to  be  adopted  in  Volumetric  Analysis      18 

10.  Preparation  of  Normal  Solutions  in  General           .                .  23 

11.  Direct  and  Indirect  Processes  of  Analysis         .                .  .28 


PART   II. 

12.  Alkalimetry        .                .                .  .  .                .30 

13.  Indicators  used  in  Saturation  Analyses  ...  30 
14-.  Normal  Alkaline  and  Acid  Solutions  .                .                .40 

15.  Correction  of  Abnormal  Solutions  ...  46 
Table  for  the  Systematic  Analysis  of  Acids,  Alkalies,  and  Alkaline 

Earths                  .                .  .  .                .49 

16.  Tit-ration  of  Alkaline  Salts                .  .  .               .50 

17.  Titration  of  Alkaline  Earths    .  .  .               .65 

18.  Ammonia           .                .                .   .  .  .                .67 

19.  Acidimetry                 .                .  .  .                .               80 

20.  Acetic  Acid        .                .                .  .  "  .                .82 

21.  Citric  Acid                 ....  85 

22.  Oxalic  Acid        .                .                .  .  .                .86 

23.  Phosphoric  Acid        .                .  .  .               86 

24.  Sulphuric  Anhydride        .                .  .  .                .87 

25.  Tartaric  Acid             .                .  .  .                .               88 

26.  Carbonic  Acid  and  Carbonates          .  .  .                .91 

27.  Estimation  of  Combined  Acids  in  Neutral  Salts    .  .  101 

28.  Extension  of  Alkalimetric  Methods  102 


Vlll  CONTENTS. 

PAET   III. 

Sect.  Page 

29.  Analysis  by  Oxidation  or  Eeduction  .               .               .    105 

30.  Permanganic  Acid  and  Perrons  Oxide     .  ..               .             106 

31.  Titration  of  Perric  Salts  by  Permanganate  .            .    .  •   •            .109 

32.  Calculation  of  Permanganate  Analyses    .  .                .  '          109 

33.  Chromic  Acid  and  Perrons  Oxide     .  .                .                .111 

34.  Iodine  and  Thiosulphate           .                .  .                .113 

35.  Analysis  of  Substances  by  Distillation  with  Hydrochloric  Acid    .     117 

36.  Arsenious  Acid  and  Iodine  121 


PAET  IV. 

37.  Analysis  by  Precipitation  ....     123 

38.  Indirect  Analyses  by  Silver  and  Potassic  Chromats  .  125 

39.  Silver  and  Thiocyanic  Acid  .  ' .  .  .127 

40.  Precision  in  Colour  Eeactions  .  .  .  128 

41.  The  Colorimeter  129 


PAET   V. 

42.  Antimony           .                .                .                .                .  .     134 

43.  Arsenic       .                .                .                .                .                .  136 

44.  Barium               .                .                .               v               .  .     141 

45.  Bismuth     .                .              -.                                .                .  142 

46.  Bromine              .                .                .                .                .  .144 

47.  Cadmium    ......  147 

48.  Calcium              .                .                .                .                .  .148 

49.  Cerium       ......  149 

50.  Chlorine              .                .                .                .                .  .149 

51.  Chlorine  Gas  and  Bleach           .                .                .                .151 
Chlorates,  lodates,  and  Bromates      .               .               .  .154 

52.  Chromium  .  .  .  .  .154 

53.  Cobalt                 .                .                .                .                .  .157 

54.  Copper       ......  160 

65.  Cyanogen  ......     173 

56.  Ferro-  and  Perri-Cyanides        ....  175 
Sulphocyanides  ......    177 

57.  Gold           .               .               .               .               .  178 

58.  Iodine                 .               .               .               .               .  .179 

59.  Perrous  Iron             .               .               .               .               .  186 

60.  Perric  Iron         .               .               .               ..  .    190 

61.  Iron  Ores  .               .               .               .               .               .  195 

62.  Lead    .                .                .                .                .                .  .    201 

63.  Magnesia  and  63A  Alumina      .                .  .             . ;             .  204 

64.  Manganese          .'              .                ..               i               .  .    206 

65.  Mercury     .               .               .               ,' '            ;.               .  219 


CONTENTS.  IX 

Sect.  Page 

66.  Nickel  .                .            ...               .              .>               .223 

67.  Nitrogen  as  Nitrates  and  Nitrites  .            SkV             *             ^^ 

68.  Oxygen  and  Hydrogen  Peroxide    ....    254 

69.  Phosphoric  Acid  and  Phosphates  .                .                .             269 

70.  Silver  '  •'*                .                .                           :    .                .284 

71.  Sugar       .  .               ..               .               .               .291 

72.  Sulphur  ...                                                .     305 

73.  Sulphuric  Acids  and  Sulphates  .                .                .             310 

74.  Sulphuretted  Hydrogen  .  .                .                .                .314 

75.  Tannic  Acid  .                .                .                                             316 

76.  Tin    .  .                .                .                .                                .    321 

77.  Uranium  .....             323 

78.  Zinc  ....  .                 .                 .     323 

79.  Vanadium  .                .                .                .               ...             332 

APPENDIX  TO  PAET  V, 

80.  Boric  Acid  and  Borates    .....     334 

81.  Oils  and  Tats  .....             336 

82.  Glycerin  .                .                .                .                .                .345 

83.  Phenol  (Carholic  Acid)  .                .                .                .348 

84.  Carhon  Disulphide         '  .  .                .                .                .     349 

85.  Molybdenum,  Tungsten,  and  Lead        .  .                .             350 


PAET   VI, 

86.  Analysis  of  Urine            .....  352 

87.  Analysis  of  Potable  Waters  and  Sewage                .                .  373 

88.  Analytical  Processes  for  "Water       .  .  .  .381 

89.  Interpretation  of  Eesults  of  Water  Analysis        .                .  419 

90.  Water  Analysis  without  Gas  Apparatus         .                .                .  429 

91.  Eeagents  and  Processes  employed           .                .                .  435 

92.  Oxygen  Dissolved  in  Water            ....  446 
Table  for  Calculations  and  Logarithms  .                .                .  448 


PAET  VII. 

93.  Volumetric  Analysis  of  Gases  and  Construction  of  Apparatus      .  452 

94.  List  of  Gases  Estimated  Directly  and  Indirectly  .  466 

95.  Hydrochloric,  Hydrobrornic,  and  Hydriodic  Acids       .  .  466 

96.  Analysis  of  Air,  Carbonic  Anhydride,  SH2,  and  SO2  .  468 

97.  Indirect  Determinations  .....  474 

98.  Improvements  in  Gas  Apparatus  .  .  .  489 

99.  Simpler  Methods  of  Gas  Analysis  ....  519 
100.  The  Nitrometer  529 


[*] 


Names   of   Elementary  Substances   occurring-  in  Volumetric 
Methods,   with  their  Symbols  and  Atomic  Weights. 


Name. 

Symbol. 

Exact  Atomic 
Weight 
as  found  by 
the  latest 
researches. 

Atomic  Weight 
adopted  in 
this  Edition. 

Aluminium 

Al 

27-3 

27-3 

Antimony 
Arsenic 

Sb 

As 

119-6 
74-9 

120-0 
75-0 

Barium 

Ba 

136-8 

136-8 

Bismuth    . 

Bi 

208-0 

208-0 

Bromine 

Br 

79-75 

80-0 

Cadmium  . 

Cd 

111-6 

111-6 

Calcium 

Ca 

39-9 

40-0 

Carbon 

C 

11-97 

12-0 

Cerium 

Ce 

141-2 

141-2 

Chlorine    . 

Cl 

35-37 

35-37 

Chromium 

Cr 

52-4 

52-4 

Cobalt       . 

Co 

58-6 

59-0 

Copper 
Gold 

Cu 

Au 

63-18 
196-2 

63-0 
196-5 

Hydrogen 
Iodine 

H 
I 

1-0 
126-5 

1-0 
126-5 

Iron    . 

Fe 

55-88 

56-0 

Lead 

Pb 

206-4 

206-4 

Magnesium     . 
Manganese 
Mercury        '  . 
Molybdenum 
Nickel 

Mg 
Mn 
Hg 
Mo 

Ni 

23-94 
55-0 
199-8 
95-8 
58-6 

24-0 
55-0 
200-0 
95-8 
59-0 

Nitrogen   . 
Oxygen 
Phosphorus 
Platinum 

N 
O 
P 
Pt 

14-01 
15-96 
30-96 
194-3 

14-0 
16-0 
31-0 
194-3 

Potassium 

K 

39-04 

39-0 

Silver 
Sodium     . 

Ag 

Na 

107-66 
22-99 

107-66 
23-0 

Strontium 

Sr 

87-2 

87-2 

Sulphur     . 
Tin     . 

S 
Sn 

31.98 
117-8 

32-0 
118-0 

Tungsten  . 
Uranium 

W 

Ur 

184-0 
239-8 

184-0 
240-0 

Vanadium 

Va 

51-2 

51-2 

Zinc    .           •  .  g 

Zn 

64-9 

65-0 

[xi] 

Abbreviations  and  Explanations. 
The   formulae   are   constructed    on   the   basis   H  =  l. 


The  normal  temperature  for  the  preparation  and  use  of  standard 
solutions  is  16°  C.,  or  about  60°  Fahr. 

c.c.  denotes  cubic  centimeter. 

gm.       „       gram  =15-43235  grains  English. 

grn.      „       grain. 

dm.      „       decem=  10  fluid  grains  at  16°  C. 

1  liter  =  1000  c.c.  at  16°  C. 

1  c.c.  =  1  gm.  distilled  water  at  16°  C. 

1  dm.  =  10  grn.          „  „ 

Distilled  water  is  to  be  used  in  all  the  processes,  unless  other- 
wise expressed. 

Normal  Solutions  are  those  which  contain  one  gram  atom  of 
reagent  (taken  as  monobasic),  or  an  equivalent  in  some  active 
constituent  (e.g.  oxygen)  in  the  liter  (see  page  23). 

Deciiiormal  Solutions  are  one-tenth  of  that  strength  =  T^-. 

Centinormal,  one  hundredth  =  TJg-. 

Empirical  Standard  Solutions  are  those  which  contain  no 
exact  atomic  proportion  of  reagent,  but  are  constructed  generally  so 
that  1  c.c.  =  O'Ol  gm.  (one  centigram)  of  the  substance  sought. 

A  Titrated  Solution  (from  the  French  word  titre,  title  or 
power)  denotes  a  solution  whose  strength  or  chemical  power  has 
been  accurately  found  by  experiment. 

When  a  chemical  substance  or  solution  is  directed  to  be  titrated, 
the  meaning  is,  that  it  is  to  be  quantitatively  tested  for  the  amount 
of  pure  substance  it  contains  by  the  help  of  standard  or  titrated 
solutions.  The  term  is  used  in  preference  to  tested  or  analyzed, 
because  these  expressions  may  relate  equally  to  qualitative  and 
quantitative  examinations,  whereas  titrations  can  only  apply  to 
quantitative  examination. 

J.  C.  S.  denotes  Journal  of  the  Chemical  Society  (Transactions 
only). 

J.  S.  C.  I.    „      Journal  of  the  Society  of  Chemical  Industry. 

Z.  a.  C.        „      Zeitschrift  fiir  Analytische  Chemie. 

C.  N.  „       Chemical  News. 

Other  book-references  are  given  in  full. 


ERltATA    AND    ADDENDA. 


Page  108.    Line  12  from  top,  substitute  for  the  words  "  new  gasvolumeter  " 
"  modified  nitrometer." 

Page  130.    The  figure  should  be  numbered  32  instead  of  30. 

Page  153.    Line  12  from  top,  read  "modified  nitrometer"  for  "new  gas- 
volumeter.'* 

Page  332.    Line  15  from  top,  the  words  "and  water"  should  be  omitted. 

Page  332.    Line  20,  after  the  words  "one  hour,"  insert,  "the  digestion  may 
be  carried  on  without  heating  with  practically  the  same  results." 

Page  332.    Line  25,  add  "  or  1  part  of  pure  zinc  should  theoretically  liberate 
0'7799  part  of  iodine." 

Page  354.    Line  10  from  top,  instead  of  the  words  "  one  place  "  read  "  two 
places." 


VOLUME  TRIG    ANALYSIS 


OF 


LIQUIDS  AND  SOLIDS, 


PART     I. 


GENERAL    PRINCIPLES. 

§  1.  QUANTITATIVE  analysis  by  weight,  or  gravimetric  analysis, 
consists  in  separating  out  the  constituents  of  any  compound,  either 
in  a  pure  state  or  in  the  form  of  some  new  substance  of  known 
composition,  and  accurately  weighing  the  products.  Such  opera- 
tions are  frequently  very  complicated,  and  occupy  a  long  time, 
besides  requiring  in  many  cases  elaborate  apparatus,  and  the  exercise 
of  much  care  and  experimental  knowledge.  Volumetric  processes, 
on  the  other  hand,  are,  as  a  rule,  quickly  performed ;  in  most  cases 
are  susceptible  of  extreme  accuracy,  and  need  much  simpler 
apparatus.  The  leading  principle  of  the  method  consists  in  sub- 
mitting the  substance  to  be  estimated  to  certain  characteristic 
reactions,  employing  for  such  reactions  solutions  of  known 
strength,  and  from  the  volume  of  solution  necessary  for  the  pro- 
duction of  such  reaction,  determining  the  weight  of  the  substance 
to  be  estimated  by  aid  of  the  known  laws  of  chemical  equivalence. 

Volumetric  analysis,  or  quantitative  chemical  analysis  by  measure, 
in  the  case  of  liquids  and  solids,  consequently  depends  upon  the 
following  conditions  for  its  successful  practice  : — 

1.  A  solution  of  the  reagent  or  test,  the  chemical  power  of 
which  is  accurately  known,  called  the  "standard  solution." 

2.  A   graduated   vessel   from   which   portions    of    it   may   be 
accurately  delivered,  called  the  "burette." 

3.  The  decomposition  produced  by  the  test  solution  with  any 
given  substance  must  either  in  itself  or  by  an  indicator  be  such, 
that  its  termination  is  unmistakable  to  the  eye,  and  thereby  the 
quantity  of  the  substance  with  which  it  has  combined  accurately 
calculated. 


ANALYSIS.  1. 


Suppose,  for  instance,  that  it  is  desirable  to  know  the  quantity  of 
pure  silver  contained  in  a  shilling.  The  coin  is  first  dissolved  in 
nitric  acid,  by  which  means  a  bluish  solution,  containing  silver, 
copper,  and  probably  other  metals,  is  obtained.  It  is  a  known  fact 
that  chlorine  combines  with  silver  in  the  presence  of  other  metals 
to  form  silver  chloride,  which  is  insoluble  in  nitric  acid.  The  pro- 
portions in  which  the  combination  takes  place  are  3  5  '3  7  of  chlorine 
to  every  107  '66  of  silver;  consequently,  if  a  standard  solution  of  pure 
sodic  chloride  is  prepared  by  dissolving  in  water  such  a  weight  of 
the  salt  as  will  be  equivalent  to  35*37  grains  of  chlorine  (  =  58*37 
grains  NaCl)  and  diluting  to  the  measure  of  1000  grains;  every 
single  grain  measure  of  this  solution  will  combine  with  0  '107  6  6  grain 
of  pure  silver  to  form  silver  chloride,  which  is  precipitated  to  the 
bottom  of  the  vessel  in  which  the  mixture  is  made.  In  the  process 
of  adding  the  salt  solution  to  the  silver,  drop  by  drop,  a  point  is  at 
last  reached  when  the  precipitate  ceases  to  form.  Here  the  process 
must  stop.  On  looking  carefully  at  the  graduated  vessel  from 
which  the  standard  solution  has  been  used,  the  operator  sees  at 
once  the  number  of  grain  measures  which  has  been  necessary  to 
produce  the  complete  decomposition.  .For  example,  suppose  the 
quantity  used  was  520  grain  measures  ;  all  that  is  necessary  to  be 
done  is  to  multiply  520  by  the  coefficient  for  each  grain  measure, 
viz.  0*10766,  which  shows  the  amount  of  pure  silver  present  to  be 
55*98  grains. 

This  method  of  determining  the  quantity  of  silver  in  any  given 
solution  occupies  scarcely  a  quarter  of  an  hour,  whereas  the  estimation 
by  weighing  could  not  be  done  in  half  a  day,  and  even  then  not  so 
accurately  as  by  the  volumetric  method.  It  must  be  understood 
that  there  are  certain  necessary  precautions  in  conducting  the  above 
process  which  have  not  been  described  ;  those  will  be  found  in  their 
proper  place  ;  but  from  this  example  it  will  at  once  be  seen  that  the 
saving  of  time  and  trouble,  as  compared  with  the  older  methods  of 
analysis,  is  immense  ;  besides  which,  in  the  majority  of  instances 
in  which  it  can  be  applied,  it  is  equally  accurate,  and  in  many  cases 
much  more  so. 

The  only  conditions  on  which  the  volumetric  system  of  analysis 
are  to  be  carried  on  successfully  are,  that  the  greatest  care  is 
exercised  with  respect  to  the  graduation  of  the  measuring  instru- 
ments, the  strength  and  purity  of  the  standard  solutions,  and  the 
absence  of  other  matters  which  would  interfere  with  the  accurate 
estimation  of  the  particular  substance  sought. 

The  fundamental  distinction  between  gravimetric  and  volumetric 
analysis  is,  that  in  the  former  method,  the  substance  to  }ye 
estimated  must  be  completely  isolated  in  the  purest  possible  state 
or  combination,  necessitating  in  many  instances  very  patient  and 
discriminating  labour  ;  whereas,  in  volumetric  processes,  such  com- 
plete separation  is  very  seldom  required,  the  processes  being  so 
contrived  as  to  admit  of  the  presence  of  half  a  dozen  or  more 


§    1.  GENERAL  PRINCIPLES.  3 

other  substances  which  have  no  effect  upon  the  particular  chemical 
reaction  required. 

The  process  just  described  for  instance,  the  estimation  of  silver 
in  coin,  is  a  case  in  point.  The  alloy  consists  of  silver  and  copper, 
with  small  proportions  of  lead,  antimony,  tin,  gold,  etc.  Xone  of 
these  things  affect  the  amount  of  salt  solution  which  is  chemically 
required  to  precipitate  the  silver,  whereas,  if  the  metal  had  to  be 
determined  by  weight  it  would  be  necessary  to  first  filter  the  nitric 
acid  solution  to  free  it  from  insoluble  tin,  gold,  etc. ;  then 
precipitate  with  a  slight  excess  of  sodic  chloride  ;  then  to  bring  the 
precipitate  upon  a  filter,  and  wash  repeatedly  with  pure  water  until 
every  trace  of  copper,  sodic  chloride,  etc.,  is  removed.  The  pure 
silver  chloride  is  then  carefully  dried,  ignited  separately  from  the 
filter,  and  weighed ;  the  filter  burnt,  residue  as  reduced  metallic  silver 
and  filter  ash  allowed  for,  and  thus  finally  the  amount  of  silver  is 
found  by  the  balance  with  ordinary  weights. 

On  the  other  hand  the  volumetric  process  has  been  purely 
chemical,  the  burette  or  measuring  instrument  has  taken  the  place 
of  the  balance,  and  theoretical  or  atomic  weights  have  supplanted 
ordinary  weights. 

The  end  of  the  operation  in  this  method  of  analysis  is  in  all 
cases  made  apparent  to  the  eye.  In  alkalimetry  it  is  the  change 
of  colour  produced  in  litmus,  turmeric,  or  other  sensitive  colouring 
matter.  The  formation  of  a  permanent  precipitate,  as  in  the 
estimation  of  cyanogen.  A  precipitate  ceasing  to  form,  as  in 
chlorine  and  silver  determination.  The  appearance  of  a  distinct 
colour,  as  in  iron  analysis  by  permanganate  solution,  and  so  on. 

I  have  adopted  the  classification  of  methods  used  by  Mohr  and 
others,  namely : 

1.  Where  the  determination   of   the  substance  is  effected  by 
saturation     with     another     substance     of     opposite     properties — 
generally   understood   to   include  acids   and   alkalies,   or   alkaline 
earths. 

2.  Where  the  determination  of  a  substance  is  effected  by  a 
reducing   or   oxidizing   agent    of   known    power,    including   most 
metals,  with  their  oxides  and  salts ;  the  principal  oxidizing  agents 
being  potassic  permanganate,  potassic  bichromate,  and  iodine ;  and 
the  corresponding  reducing  agents,  ferrous  and  stannous  compounds, 
and  sodic  thiosulphate. 

3.  Where   the   determination   of    a   substance   is  effected    by 
precipitating  it  in  some  insoluble   and   definite    combination,   an 
•example    of  which  occurs   in    the  estimation  of   silver  described 
above. 

This  classification  does  not  rigidly  include  all  the  volumetric 
processes  that  may  be  used,  but  it  divides  them  into  convenient 
.sections  for  describing  the  peculiarity  of  the  reagents  used,  and 
their  preparation.  If  strictly  followed  out,  it  would  in  some  cases 
necessitate  the  registration  of  the  body  to  be  analyzed  under  two 

B  2 


4  VOLUMETRIC   ANALYSIS.  §    1. 

or  three  heads.  Copper,  for  instance,  can  be  determined  residually 
by  potassic  permanganate  ;  it  can  also  be  determined  by  precipitation 
with  sodic  sulphide.  The  estimation  of  the  same  metal  by  potassic 
cyanide,  on  the  other  hand,  would  not  come  under  any  of  the 
heads. 

It  will  be  found,  therefore,  that  liberties  have  been  taken  with  the 
arrangement ;  and  for  convenient  reference  all  analytical  processes 
applicable  to  a  given  body  are  included  under  its  name. 

It  may  be  a  matter  of  surprise  to  some  that  several  distinct 
volumetric  methods  for  one  and  the  same  substance  are  given ; 
but  a  little  consideration  will  show  that  in  many  instances  greater 
convenience,  and  also  accuracy,  may  be  gained  in  this  way.  The 
operator  may  not  have  one  particular  reagent  at  command,  or  he 
may  have  to  deal  with  such  a  mixture  of  substance  as  to  preclude 
the  use  of  some  one  method ;  whereas  another  may  be  quite 
free  from  such  objection.  The  choice  in  such  cases  of  course 
requires  judgment,  and  it  is  of  the  greatest  importance  that  the 
operator  shall  be  acquainted  with  the  qualitative  composition  of  the 
matters  with  which  he  is  dealing,  and  that  he  should  ask  himself 
at  every  step  why  such  and  such  a  thing  is  done. 

It  will  be  apparent  from  the  foregoing  description  of  the 
volumetric  system,  that  it  may  be  successfully  used  in  many 
instances  by  those  who  have  never  been  thoroughly  trained  as 
analytical  chemists ;  but  we  can  never  look  for  the  scientific 
development  of  the  system  in  such  hands  as  these. 

In  the  preparation  of  this  work  an  endeavour  has  been  made  to- 
describe  all  the  operations  and  chemical  reactions  as  simply  as 
possible,  purposely  avoiding  abstruse  mathematical  expressions, 
which,  though  they  may  be  more  consonant  with  the  modern  study 
of  chemical  science,  are  hardly  adapted  to  the  technical  operator. 


§    2.  INSTRUMENTS. 


THE   INSTRUMENTS  AND  APPARATUS. 

THE    BALANCE. 

$  2.  STRICTLY  speaking,  it  is  necessary  to  have  two  balances  in 
order  to  carry  out  the  volumetric  system  completely ;  one  to  carry 
about  a  kilogram  in  each  pan,  and  turn  when  loaded  with 
about  five  milligrams.  This  instrument  is  used  for  graduating 
flasks,  or  for  testing  them,  and  for  weighing  large  amounts  of  pure 
reagents  for  standard  solutions.  The  second  balance  should  be 
light  and  delicate,  and  to  carry  about  fifty  grams,  and  turn  easily 
and  quickly  when  loaded  with  one  or  two-tenths  of  a  milligram. 
This  instrument  serves  for  weighing  small  quantities  of  substances 
to  be  tested,  many  of  which  are  hygroscopic,  and  need  to  be 
weighed  quickly  and  with  great  accuracy ;  it  also  serves  for  testing 
the  accuracy  of  pipettes  and  burettes. 

For  all  technical  purposes,  however,  a  moderate-sized  balance 
of  medium  delicacy  is  quite  sufficient,  especially  if  rather  large 
quantities  of  substances  are  weighed  and  brought  into  solution — 
then  further  subdivided  by  means  of  measuring  flasks  and  pipettes. 

The  operator  also  requires,  besides  the  balance  and  the  graduated 
instruments,  a  few  beakers,  porcelain  basins,  flasks,  funnels,  stirring 
rods,  etc.,  as  in  gravimetric  analysis ;  above  all  he  must  be 
practically  familiar  with  proper  methods  of  filtration,  washing  of 
precipitates,  and  the  application  of  heat. 

VOLUMETRIC    ANALYSIS    WITHOUT    WEIGHTS. 

§  3.  THIS  is  more  a  matter  of  curiosity  than  of  value ;  but, 
nevertheless,  one  can  imagine  circumstances  in  which  it  might  be 
useful.  In  carrying  it  out,  it  is  necessary  only  to  have  (1)  a 
correct  balance,  (2)  a  pure  specimen  of  substance  to  use  as  a  weight, 
(3)  an  accurate  burette  filled  with  the  appropriate  solution.  It  is 
not  necessary  that  the  strength  of  this  should  be  known ;  but  the 
state  of  concentration  should  be  such  as  to  permit  the  necessary 
reaction  to  occur  under  the  most  favourable  circumstances. 

If  a  perfectly  pure  specimen  of  substance,  say  calcic  carbonate, 
be  put  into  one  scale  of  the  balance,  and  be  counterpoised  Avith  an 
impure  specimen  of  the  same  substance,  and  both  titrated  with  the 
same  acid,  and  the  number  of  c.c.  used  for  the  pure  substance  be 
called  100,  the  number  of  c.c.  used  for  the  impure  substance  will 
correspond  to  the  percentage  of  pure  calcic  carbonate  in  the  specimen 
examined. 

The  application  of  the  process  is,  of  course,  limited  to  the  use  of 
such  substances  as  are  to  be  had  pure,  and  whose  weight  is  not 
variable  by  exposure  ;  but  where  even  a  pure  substance  of  one  kind 
cannot  be  had  as  a  weight,  one  of  another  kind  may  be  used  as  a 
substitute,  and  the  required  result  obtained  by  calculation.  For 


6  VOLUMETRIC   ANALYSIS.  §    4. 

instance,  it  is  required  to  ascertain  the  purity  of  a  specimen  of  sodic 
carbonate,  and  only  pure  calcic  carbonate  is  at  hand  to  use  as  a 
weight ;  equal  weights  of  the  two  are  taken,  and  the  impure  speci- 
men titrated  with  acid.  To  arrive  at  the  required  answer,  it  is 
necessary  to  find  a  coefficient  or  factor  by  which  to  convert  the 
number  of  c.c.  required  by  the  sodic  carbonate,  weighed  on  the  calcic, 
into  that  Avhicli  should  be  required  if  weighed  on  the  sodic,  basis. 
A  consideration  of  the  relative  molecular  weights  of  the  two  bodies 
will  give  the  factor  thus- 
Calcic  carbonate  100 
Sodic  carbonate  106~~ 

If,  therefore,  the  c.c.  used  are  multiplied  by  this  number,  the 
percentage  of  pure  sodic  carbonate  will  be  obtained.  The  method 
may  be  extended  to  a  number  of  substances,  on  this  principle,  with 
the  exercise  of  a  little  ingenuity. 

L.  de  Koningh  has  communicated  to  me  a  similar  method 
devised  by  himself  and  Peacock,  in  which  the  same  end  is 
attained  without  the  aid  of  a  pure  substance  as  standard,  thus : 
Say  a  specimen  of  impure  common  salt  is  to  be  examined,  a 
moderate  portion  is  put  on  the  balance  and  counterpoised  with 
silver  nitrate ;  the  latter  is  then  dissolved  up  to  100  c.c.  and  placed 
in  a  burette.  The  salt  is  dissolved  in  water,  a  few  drops  of 
chromate  added  and  titrated  with  the  silver  solution,  of  which 
10  c.c.  is  required ;  the  salt  is  therefore  equal  to  10  per  cent, 
of  its  weight  of  silver  nitrate,  then — 

16-96  :  58-37  :  :  10  =  3'44  %  NaCl 

Or,  in  the  case  of  an  impure  soda  ash,  an  equal  weight  of  oxalic 
acid  is  taken  and  made  up  to  100  c.c. ;  the  soda  requires,  say, 
50  c.c.  for  saturation,  or  50  per  cent.,  then — 

126  :  106  :  :  50  =  42  %  ISTa2C03 

It  may  happen  that,  in  some  cases,  more  than  one  portion  of  the 
reagent  is  required  to  decompose  the  substance  tested,  and  to 
provide  against  this  two  or  more  lots  should  be  weighed  in  the 
first  instance. 

VOLUMETRIC    ANALYSIS    WITHOUT    BURETTES    OR 
OTHER    GRADUATED    INSTRUMENTS. 

§  4.  THIS  operation  consists  in  weighing  the  standard  solutions 
on  the  balance  instead  of  measuring  them.  The  influence  of 
variation  in  temperature  is,  of  course,  here  of  no  consequence.  The 
chief  requisite  is  a  delicate  flask,  fitted  with  a  tube  and  blowing 
ball,  as  in  the  burette  fig.  7,  or  an  instrument  known  as 
Schuster's  alkalimeter  may  be  used.  A  special  burette  has  been 
devised  for  this  purpose  by  Casamajor  ((7.  -ZV.  xxxv.  98).  The 


INSTRUMENTS. 


method  is  capable  of  very  accurate  results,  if  care  be  taken  in 
preparing  the  standard  solutions  and  avoiding  any  loss  in  pouring 
the  liquid  from  the  vessel  in  which  it  is  weighed.  It  occupies 
much  more  time  than  the  usual  processes  of  volumetric  analysis, 
but  at  great  extremes  of  temperature  it  is  far  more  accurate. 

THE    BURETTE. 

§  5.  THIS  instrument  is  used  for  the  delivery  of  an  accurately 
measured  quantity  of  any  particular  standard  solution.  It  invari- 
ably consists  of  a  long  glass  tube  of  even  bore,  throughout  the 


Fig.  1. 


Fig.  2. 


length  of   which  are    engraved,   by  means    of   hydrofluoric   acid, 
certain  divisions  corresponding  to  a  known  volume  of  fluid. 


8 


VOLUMETKIC  ANALYSIS. 


It  may  be  obtained  in  a  great  many  forms,  under  the  names  of  their 
respective  inventors,  such  as  Mohr,  Gay  Lussac,  Binks,  etc., 
but  as  some  of  these  possess  a  decided  superiority  over  others,  it  is 
not  quite  a  matter  of  indifference  which  is  used,  and  therefore  a 
slight  description  of  them  may  not  be  out  of  place  here.  The 
burette,  with  india-rubber  tube  and  clip,  contrived  by  Mohr,  is 
shown  in  figs.  1  and  2,  and  with  stop-cock  in  fig.  3. 


Fig.  3.  Fig.  4. 

The  advantages  possessed  by  this  form  of  instrument  are, 
that  its  fixed  upright  position  enables  the  operator  at  once 
to  read  off  the  number  of  degrees  of  test  solution  used  for  any 
analysis.  The  quantity  of  fluid  to  be  delivered  can  be  regulated 
to  the  greatest  nicety  by  the  pressure  of  the  thumb  and  finger 
on  the  spring  clip  or  by  the  tap ;  and  the  instrument  not  being 
held  in  the  hand,  there  is  no  chance  of  increasing  the  bulk  of 
the  fluid  by  the  heat  of  the  body,  and  thus  leading  to  incorrect 
measurement,  as  is  the  case  with  Binks' or  Gay  Lussac's  form 


§ 


INSTRUMENTS. 


9 


of  instrument.  The  principal  disadvantage,  however,  of  these  two 
latter  forms  of  burette  is,  that  a  correct  reading  can  only  be 
obtained  by  placing  them  in  an  upright  position,  and  allowing 
the  fluid  to  find  its  perfect  level.  The  preference  should,  therefore, 
unhesitatingly  be  given  to  Mohr's  burette,  wherever  it  can  be 
used ;  the  greatest  drawback  to  its  original  form  is,  that  it  cannot 
be  used  for  permanganate,  and  some  other  solutions  affected  by  the 
india-rubber.  This  defect  is  avoided  by  using  the  stop-cock 
burette,  fig.  3.  This  tap  burette  may  of  course  be  used  not  only 


for  permanganate  but  for  all  other  solutions,  and  may  also  be 
arranged  so  as  to  deliver  the  solution  in  drops,  leaving  both  the 
hands  of  the  operator  disengaged.  A  new  and  ingenious  arrange- 
ment of  tap  is  shown  in  fig.  4,  the  tap  being  placed  obliquely 
through  the  spit,  so  as  to  avoid  its  dropping  out  of  place;  the 
floats  shown  are  very  small  thermometers.  Owing  to  the  action  of 


10 


VOLUMETRIC   ANALYSIS. 


§  5. 


caustic  alkalies  upon  glass,  such  a  burette  does  not  answer  well  for 
strong  solutions  of  potash  or  soda,  unless  emptied  and  washed 
immediately  after  use.  Two  convenient  forms  of  stand  for  Mohr's 
burettes  are  shown  in  figs.  5  and  6  ;  in  the  latter,  the  arms  carrying 
the  burettes  revolve. 

We  are  indebted  to  Mohr  for  another  form  of  instrument  to 
avoid  the  contact  of  permanganate  and  india-rubber,  viz.,  the  foot 
burette,  with  elastic  ball,  shown  in  fig.  7. 

The  flow  of  liquid  from  the 
exit  tube  can  be  regulated  to 
a  great  nicety  by  pressure 
upon  the  ball,  which  should 
be  large,  and  have  'two  open- 
ings,— one  cemented  to  the 
tube  with  marine  glue,  and 
the  other  at  the  side,  over 
which  the  thumb  is  placed 
when  pressed,  and  on  the 
removal  of  which  it  refills 
itself  with  air. 

Gay  Lussac's  burette, 
supported  in  a  wooden  foot, 
may  be  used  instead  of  the 
above  form,  by  inserting  a 
good  fitting  cork  into  the 
open  end,  through  which  a 
small  tube  bent  at  right 
angles  is  passed.  If  the 
burette  is  held  in  the  right 
hand,  slightly  inclined  to- 
wards the  beaker  or  flask 
into  which  the  fluid  is  to  be 
measured,  and  the  mouth 
applied  to  the  tube,  any 
portion  of  the  solution  may 
be  emptied  out  by  the  pressure 

of  the  breath,  and  the  disadvantage  of  holding  the  instrument  in 
a  horizontal  position,  to  the  great  danger  of  spilling  the  contents, 
is  avoided ;  at  the  same  time  the  beaker  or  flask  can  be  held 
in  the  left  hand  and  shaken  so  as  to  mix  the  fluids,  and  by 
this  means  the  end  of  the  operation  be  more  accurately  determined 
(see  fig.  8). 

There  is  an  arrangement  of  Mohr's  burette  which  is  extremely 
serviceable,  when  a  series  of  analyses  of  the  same  character  have 
to  be  made,  such  as  in  alkali  works,  assay  offices,  etc.  It  consists 
in  having  a  ~]~  piece  of  glass  tube  inserted  between  the  lower 
end  of  the  burette  and  the  spring  clip,  which  communicates  with 
a  reservoir  of  the  standard  solution,  placed  above  so  that  the 


Tig.  7. 


Fig.  8. 


§    5.  INSTKUMENTS.  11 

burette  may  be  filled  as  often  as  emptied,  by  a  syphon,  and  in  so 
gradual  a  manner  that  110  air  bubbles  occur,  as  in  the  case  of  filling 
it  with  a  funnel,  or  pouring  in  liquid  from  a  bottle ;  beside  which, 
this  plan  prevents  evaporation  or  dust  in  the  standard  solution 
either  in  the  burette  or  reservoir. 

Figs.  9  and  10  show  this  arrangement  in  detail. 


HUBERT  DYER 


rig.  9. 

It  sometimes  happens  that  a  solution  requires  titration  at  a  hot  or 
even  boiling  temperature,  such  as  the  estimation  of  sugar  by  copper 
solution :  here  the  ordinary  arrangement  of  Mohr's  burette  will 
not  be  available,  since  the  steam  rising  from  the  liquid  heats  the 
burette  and  alters  the  volume  of  fluid.  This  may  be  avoided  either 
by  using  a  special  burette,  in  which  the  lower  end  is  extended  at  a 
right  angle  with  a  stop-cock,  or  by  attaching  to  an  ordinary  burette 
a  much  longer  piece  of  india-rubber  tube,  so  that  the  burette 
stands  at  the  side  of  the  capsule  or  beaker  being  heated,  and  the 


12 


VOLUMETRIC   ANALYSIS. 


§  5. 


elastic   tube   is   brought  over  its  edge ;    the  pinch-cock  is  fixed 
midway ;  no  heat  can  then  reach  the  body  of  fluid  in  the  burette, 
since  there  can  be  no  conduction  past  the  pinch-cock.     If  this  plan 
is  not  adopted,  a  Gay  Lussac  or  ball  burette  should  be  used. 
Gay  Lus sac's  burette,  shown  in  fig.  11,  should  have  a  wooden 


Fig.  10. 


Fig.  11. 


support  or  foot  into  which  it  may  be  inserted  (fig.  8),  so  as  to  lie 
read  correctly.  By  using  it  in  the  following  manner,  its  natural 
disadvantages  may  be  overcome  to  a  great  extent.  Having  fixed 
the  burette  into  the  foot  securely,  and  filled  it,  take  it  up  by  the 
foot  with  the  left  hand,  and  resting  the  upper  end  upon  the  edge 


§5. 


INSTRUMENTS. 


13 


of  the  beaker  in  which  the  solution  to  be  tested  is  placed,  drop 
the  test  fluid  from  the  burette,  meanwhile  stirring  the  contents 
of  the  beaker  with  a  glass  rod  held  in  the  right  hand ;  by  a  slight 
elevation  or  depression  of  the  left  hand,  the  flow  of  test  liquid 
is  regulated  until  the  end  of  the  operation  is  secured,  thus  avoiding 
the  annoyances  which  arise  from  alternately  placing  the  instrument 
in  an  upright  and  horizontal  position. 


Binks',  or,  as  it  is  sometimes  called,  the  English  burette,  is  well 
known,  and  need  not  be  described ;  it  is  the  least  recommendable 
of  all  forms,  except  for  very  rough  estimations. 

It  is  most  convenient  to  have  burettes  graduated  to  contain  25 
or  30  c.c.  in  y1^  c.c.,  50  or  60  c.c.  in  4  c.c.,  and  100  or  110  c.c.  in 
J  or  y  c.c. 

The  pinch-cock  generally  used  in  Mohr's  burette  is  shown  in 
fig.  1 .  These  are  made  of  brass  and  are  now  generally  nickel-plated 
to  prevent  corrosion ;  another  form  is  made  of  one  piece  of  steel 
wire,  as  devised  by  Hart ;  the  wire  is  softened  by  heating  and 
coiled  round,  as  shown  in  fig.  12.  When  the  proper  shape  has 
been  attained,  the  clip  is  hardened  and  tempered  so  as  to  convert  it 
into  a  spring. 

Another  useful  pinch-cock  is  shown  in  fig.  12.  It  may  be  made 
of  hard  wood,  horn,  or  preferably,  of  flat  glass  rod.  The  levers 
should  be  long.  A  small  piece  of  cork,  of  the  same  thickness  as 
the  elastic  tube  of  the  burette  when  pressed  close,  should  be 
fastened  at  the  angles  of  the  levers  as  shown  in  the  engraving. 

The  use  of  any  kind  of  pinch-cock  may  be  avoided,  and  a  very 
delicate  action  obtained,  by  simply  inserting  a  not  too  tightly  fitting 
piece  of  solid  glass  rod  into  the  elastic  tube,  between  the  end  of  the 


VOLUMETEIC   ANALYSIS. 


§ 


burette  and  the  spit,  a  firm  squeeze  being  given  by  the  finger  and 
thumb  to  the  elastic  tube  surrounding  the  rod,  a  small  canal  is 
opened,  and  thus  the  liquid  escapes,  and  of  course  can  be  controlled 
by  the  operator  at  his  will  (see  fig.  13). 


50  CC 


10CC 


Pig.  13. 


Fig.  14. 


THE    PIPETTE. 


§  6.  THE  pipettes  used  in  volumetric  analysis  are  of  two  kinds, 
viz.,  those  which  deliver  one  certain  quantity  only,  and  those  which 
are  graduated  on  the  stem,  so  as  to  deliver  various  quantities  at  the 
discretion  of  the  analyst.  In  the  former  kind,  or  whole  pipette, 
the  graduation  may  be  either  that  in  which  the  fluid  is  suffered  to 
run  out  by  its  own  weight,  or  in  which  it  is  blown  out  by  the 
breath.  The  best  form  is  that  in  which  the  liquid  flows  out  by  its 


INSTRUMENTS. 


15 


own  weight,  but  in  this  case  the  last  few  drops  empty  themselves 
very  slowly ;  if,  however,  the  lower  end  of  the  pipette  be  touched 
against  the  moistened  edge  of  the  beaker  or  the  surface  of  the  fluid 
into  which  it  is  emptied,  the  flow  is  hastened  considerably,  and  in 
graduating  the  pipette,  it  is  preferable  to  adopt  this  plan. 

In  both  the  whole  and  graduated  pipettes,  the  upper  end  is 
narrowed  to  about  -J  inch,  so  that  the  pressure  of  the  finger  is 
sufficient  to  arrest  the  flow  at  any  point. 

Pipettes  are  invariably  filled  by  sucking  the  upper  end  with  the 
mouth,  unless  the  liquid  contain  volatile  or  other  highly  poisonous 
matter,  in  which  case  the  instrument  may  be  dipped  completely 
into  the  fluid,  but  if  so  the  outside  liquid  must  be  wiped  off 
before  measuring.  Beginners  invariably  find  a  difficulty  in  quickly 
filling  the  pipette  above  the  mark,  and  stopping  the  fluid  at  the 
exact  point.  Practice  with  pure  water  is  the  only  method  of  over- 
coming this. 

Fig.  14  shows  two  whole  pipettes,  one  of  small  and  the  other  of 
large  capacity,  and  also  a  graduated  pipette  of  medium  size.  It 
must  be  borne  in  mind  that  the  pipette  graduated  throughout  the 
stem  is  not  a  reliable  instrument  for  actual  analysis,  owing  to  the 
difficulty  of  stopping  the  flow  of  liquid  at  any  given  point,  and 
reading  off  the  exact  measurement.  Its  chief  use  is  in  the 
approximate  estimation  of  the  strength  of  any  standard  solution 
in  the  course  of  preparation. 

THE    MEASURING    FLASKS. 

§  7.  THESE  indispensable  instru- 
ments are  made  of  various  capacities ; 
they  serve  to  mix  up  standard  solu- 
tions to  a  given  volume,  and  also 
for  the  subdivision  of  the  substance 
to  be  tested  by  means  of  the  pipettes. 
They  should  be  tolerably  wide  at  the 
mouth,  and  have  a  well-ground  glass 
stopper,  and  the  graduation  line 
should  fall  just  below  the  middle  of 
the  neck,  so  as  to  allow  room  for 
shaking  up  the  fluid.  Convenient 
sizes  are  100,  200,  250,  300,  500, 
and  1000  c.c.,  all  graduated  to  contain 
the  respective  quantities.  If  required 
to  deliver  these  volumes  they  must 
have  a  second  higher  mark  in  the 
neck,  obtained  by  weighing  into 
the  wetted  and  drained  flasks  the 
respective  number  of  grams  of  dis- 
tilled water  at  16°  C.  A  liter  flask 
is  shown  in  fig.  15.  Fig.  15. 


16 


VOLUMETRIC  ANALYSIS. 


ON    THE    CORRECT    READING    OF    GRADUATED 
INSTRUMENTS. 

§  8.  THE  surface  of  liquids  contained  in  narrow  tubes  is  always 
curved,  in  consequence  of  the  capillary  attraction  exerted  by  the 
sides  of  the  tube,  and  consequently  there  is  a  difficulty  in  obtaining 

a  distinct  level  in  the  fluid 
to  be  measured.  If,  how- 
ever, the  lowest  point  of  the 
curve  is  made  to  coincide 
with  the  graduation  mark, 
a  correct  proportional  read- 
ing is  always  obtained,  hence 
this  method  of  reading  is  the 
most  satisfactory  (see  fig.  1 6). 
The  eye  may  be  assisted 
materially  in  reading  the 
divisions  on  a  graduated 
tube  by  using  a  small  card, 
Fig.  16.  the  lower  half  of  which  is 

blackened,  the  upper  re- 
maining white.  If  the  line  of  division  between  the  black  and 
white  be  held  about  an  eighth  of  an  inch  below  the  surface  of  the 
liquid,  and  the  eye  brought  on  a  level  with  it,  the  meniscus  then 
can  be  seen  by  transmitted  light,  bounded  below  by  a  sharply 
denned  black  line.  A  card  of  this  kind,  sliding  up  and  down  a 
support,  is  of  great  use  in  verifying  the  graduation  of  the  burettes 
or  pipettes  with  a  cathetometer.  Another  good  method 
is  to  use  a  piece  of  mirror,  upon  which  are  gummed 
two  strips  of  black  paper,  half  an  inch  apart ;  apply  it 
in  contact  with  the  burette  so  that  the  eye  can  be 
reflected  in  the  open  space.  The  burette  or  pipette  is 
filled  with  water  at  the  proper  temperature,  and  the 
contents  of  each  division  of  10  c.c.  or  so  carefully  read 
off  with  the  telescope  and  weighed.  In  order  to  do 
this  with  pipettes  they  must  be  fixed  in  a  burette 
support,  and  have  over  their  upper  end  a  tightly  fitting 
elastic  tube  closed  with  a  pinch-cock.  The  operator 
may  here  consult  with  advantage  the  details  of  gradu- 
ating and  verifying  measuring  instruments  for  the 
analysis  of  gases  as  described  in  Part  7.  In  taking 
the  readings  of  burettes,  pipettes,  and  flasks,  the 
graduation  mark  should  coincide  as  nearly  as  possible 
with  the  level  of  the  operator's  eye. 
Erdmann's  Float.  This  useful  little  instrument  to  accompany 
Mohx's  burette,  gives  the  most  accurate  reading  that  can  be 
obtained ;  one  of  its  forms  is  shown  in  fig.  17,  another,  containing 
a  thermometer,  is  shown  in  fig.  4.  It  consists  of  an  elongated 


Fig.  17. 


§ 


COllliECT   READINGS. 


glass  bulb,  rather  smaller  in  diameter  than  the  burette  itself,  and 
weighted  at  the  lower  end  with  a  globule  of  mercury,  like  an 
hydrometer.  It  is  drawn  to  a  point  at  the  upper  end,  and  the 
point  is  bent  round  so  as  to  form  a  small  hook,  by  means  of  which 
it  can  be  lifted  in  and  out  of  the  burette  with  a  bent  wire ;  a  line 
is  made  with  a  diamond  round  its  middle  by  means  of  a  lathe, 
and  the  coincidence  of  this  line  with  the  graduation  mark  of  the 
burette  is  accepted  as  the  true  reading.  The  actual  height  of  the 
liquid  in  the  burette  is  not  regarded,  because  if  the  operator  begins 
with  the  line  on  the  float,  opposite  the  0  graduation  mark  on  the 
burette,  the  same  proportional  division  is  always  maintained. 

It  is  essential  that  the  float 
should  move  up  and  down  in 
the  burette  without  wavering, 
and  the  circle  upon  it  should 
always  be  parallel  to  the 
graduations  of  the  burette. 
One  great  value  of  this  float 
is  found  in  testing  the  accuracy 
of  the  burette  itself;  it  enables 
a  strict  comparison  to  be  made 
between  say  each  10  c.c.,  with 
very  slight  differences  in  weigh- 
ing, supposing  the  instrument 
to  be  .correct.  It  is  always 
well,  however,  to  bear  in  mind 
that  absolute  accuracy  cannot 
be  obtained  in  graduating  in- 
struments ;  5  or  10  milligrams 
of  water  either  way  in  10  c.c. 
may  safely  be  disregarded. 

To  prevent  evaporation  and 
the  entrance  of  dust  in  Mohr's 
burette,  while  in  use,  a  small 
beaker  or  wide  test  tube  should 
be  dropped  over  its  orifice.  In 
burettes  containing  caustic  al- 
kaline solutions,  a  cork  with 
carbonic  acid  tube  should  be 
used  if  the  solution  is  allowed 
to  remain  in  them  for  any 
length  of  time. 

Besides  the  measuring  flasks 
it  is  necessary  to  have  graduated 


Fig.  18. 


vessels  of  cylindrical  form,  for  the  purpose  of  preparing  standard 
solutions,  etc. 

Fig.  18  shows  a  stoppered  cylinder  for  this  purpose,  generally 
called  a  test  mixer. 


18  VOLUMETRIC   ANALYSIS.  §    9. 

Filter  for  ascertaining:  the  end-reaction  in  certain  pro- 
cesses. This  is  shown  in  fig.  19,  and  the  instrument  is 
known  as  Beale's  filter.  It  serves  well  for  taking  a  few 
drops  of  clear  solution  from  any  liquid  in  which  a  pre- 
cipitate wrill  not  settle  readily.  To  use  it,  a  piece  of  filter 
paper  is  tied -over  the  lower  end,  and  over  that  a  piece  of 
fine  muslin  to  keep  the  paper  from  being  broken.  When 
dipped  into  a  muddy  mixture,  the  clear  fluid  rises  and 
may  be  poured  out  of  the  little  spout  for  testing.  If  the 
process  in  hand  is  not  completed,  the  contents  are  washed 
back  to  the  bulk,  and  the  operation  repeated  as  often  as 
may  be  required.  Fig.  19. 

ON      THE      SYSTEM      OF      WEIGHTS      AND      MEASURES 
TO    BE    ADOPTED    IN    VOLUMETRIC    ANALYSIS. 

§  9.  IT  is  much  to  be  regretted  that  the  decimal  system  of 
weights  and  measures  used  on  the  Continent  is  not  universally 
adopted,  for  scientific  and  medicinal  purposes,  in  England.  Its 
great  advantage  is  its  uniformity  throughout.  The  unit  of  weight 
is  the  gram  (  =  15'43235  grains  troy),  and  a  gram  of  distilled 
water  at  4°  C.,  or  39°  Fahr.,  measures  exactly  a  cubic  centimeter. 
The  kilogram  contains  1000  grams,  the  liter  1000  cubic  centi- 
meters. 

It  may  not  be  out  of  place  here  to  give  a  short  description  of  the 
origin  of  the  French  decimal  system,  now  used  exclusively  for 
scientific  purposes  in  that  country,  and  also  in  Prussia,  Austria, 
Holland,  Sweden,  Denmark,  Belgium,  and  Spain. 

The  commission  appointed  in  France  for  the  purpose  of  instituting 
a  decimal  system  of  weights  and  measures,  founded  their  standard 
on  the  length  of  the  meridian  arc  between  the  pole  and  equator, 
the  ten-millionth  part  of  which  was  called  the  metre  (  =  39 '37 10 
English  inches),  although  the  accuracy  of  this  measurement  has 
been  disputed.  It  would  have  been  preferable,  as  since  proposed, 
that  the  length  of  a  pendulum  vibrating  exactly  86,400  times  in 
twenty-four  hours,  or  one  second  for  each  vibration,  equivalent  to 
39 '137 2  English  inches,  should  have  been  taken  as  the  standard 
metre,  in  which  case  it  would  have  been  much  easier  to  verify  the 
standard  in  case  it  should  be  damaged  or  destroyed.  However,  the 
actual  metre  in  use  is  equal  to  3  9 '3 71  inches,  and  from  this  standard 
its  multiples  and  subdivisions  all  proceed  decimally ;  its  one-tenth 
part  being  the  decimetre,  one-hundredth  the  centimetre,  and  one- 
thousandth  the  millimetre. 

In  accordance  with  this,  a  cube  of  distilled  water  at  its  greatest 
density,  viz.,  4°  C.,  or  39°  Fahr.,  whose  side  measures  one  decimeter, 
has  exactly  the  weight  of  one  kilogram,  or  1 000  grams,  and  occupies 
the  volume  of  one  liter,  or  1000  cubic  centimeters. 

This  simple  relationship  between  liquids  and  solids  is  of  great 


§    9.  WEIGHTS   AND   MEASURES.  19 

value  in  a  system  of  volumetric  analysis,  and  even  for  ordinary 
analysis  by  weight ;  for  technical  purposes  it  is  equally  as  applicable 
as  the  grain  system,  the  results  being  invariably  tabulated  in 
percentages. 

With  these  brief  explanations,  therefore,  I  have  only  to  state 
that  the  French  decimal  system  will  be  mainly  used  throughout 
this  treatise  ;  but  at  the  same  time,  those  who  may  desire  to  adhere 
to  the  ordinary  grain  weights,  can  do  so  without  interfering  with 
the  accuracy  of  the  processes  described. 

As  has  been  before  stated,  the  true  cubic  centimeter  contains 
one  gram  of  distilled  water  at  its  greatest  density,  viz.,  4°  C., 
or  39°  Fahr. ;  but  as  this  is  a  degree  of  temperature  at  which  it 
is  impossible  to  work  for  more  than  a  month  or  two  in  the  year,  it 
is  better  to  take  the  temperature  of  16°  C.,  or  about  60°  Fahr.,  as 
the  standard ;  because  in  winter  most  laboratories  or  rooms  have 
furnaces  or  other  means  of  warmth,  and  in  summer  the  same 
localities  ought  not,  under  ordinary  circumstances,  to  have  a  much 
higher  degree  of  heat  than  16°  C.  In  order,  therefore,  that  the 
graduation  of  instruments  on  the  metrical  system  may  be  as 
uniform  as  possible  with  our  own  fluid  measures,  the  cubic 
centimeter  should  contain  one  gram  of  distilled  water  at  16°  C. 
The  true  c.c.  (i.e.  —  1  gm.  at  4°  C.,  or  39°  Fahr.)  contains  only 
0-999  gm.  (strictly  0'998981)  at  that  temperature;  but  for  con- 
venience of  working,  and  for  uniformity  with  our  own  standards 
of  volume,  it  is  better  to  make  the  c.c.  contain  one  gram  at  16°  C. 
The  real  difference  is  one-thousandth  part.  The  operator,  there- 
fore, supposing  he  desires  to  graduate  his  own  measuring  flasks, 
must  weigh  into  them  250,  500,  or  1000  grams  of  distilled  water 
at  16°  C.,  or  60°  Fahr. 

Fresenius  and  others  have  advocated  the  use  of  the  strict  liter 
by  the  graduation  of  instruments,  so  that  they  shall  contain 
999  gm.  at  16°  C.  Mohr,  on  the  contrary,  uses  a  1000  gm.,  at 
the  temperature  of  17 '5°,  the  real  difference  being  1'2  c.c.  in  the 
liter,  or  about  one  eight-hundredth  part. 

It  will  be  seen  above  that  I  have  advocated  a  middle  course  on 
two  grounds:  (1)  That  in  testing  instruments  it  is  much  easier 
to  verify  them  by  means  of  round  numbers,  such  as  5  or  10  gm. 
(2)  That  there  are  many  thousands  of  instruments  already  in  use 
varying  between  the  two  extremes ;  and  as  these  cannot  well  be 
annihilated,  the  adoption  of  a  mean  will  give  a  less  probable  amount 
of  error  between  the  respective  instruments ;  and,  moreover,  the 
difference  between  the  liter  at  4°  and  16°  being  one-thousandth 
part,  it  is  easy  to  correct  the  measurement  for  the  exact  liter. 

It  matters  not  which  plan  is  followed,  if  all  the  instruments  in 
a  particular  set  coincide  with  each  other;  but  it  would  be 
manifestly  wrong  to  use  one  of  Mohr's  burettes  with  one  of 
Fresenius'  measuring  flasks.  Operators  can,  however,  without 
much  difficulty  re-mark  their  measuring  flasks  to  agree  with  their 

c  2 


20 


VOLUMETRIC   ANALYSIS. 


smaller  graduated  instruments,  if  they  are  found  to  differ  to  any 
material  extent. 

Variations  of  Temperature. — 111  the  preparation  of  standard 
solutions,  one  thing  must  especially  be  borne  in  mind ;  namely, 
that  saline  substances  on  being  dissolved  in  water  have  a  consider- 
able effect  upon  the  volume  of  the  resulting  liquid.  The  same  is 
also  the  case  in  mixing  solutions  of  various  salts  or  acids  with  each 
other  (see  Gerlach,  "  Specifische  Gewichte  der  Salzlosungen ; " 
also  Gerlach,  "  Sp.  Gewichte  von  wasserigen  Lb'sungen,"  Z.  a.  C. 
viii.  245). 

In  the  case  of  strong  solutions,  the  condensation  in  volume  is  as 
a  rule  considerable  :  and,  therefore,  in  preparing  such  solutions  for 
volumetric  analysis,  or  in  diluting  such  solutions  to  a  given  volume 
for  the  purpose  of  removing  aliquot  portions  subsequently  for 
examination,  sufficient  time  must  be  given  for  liquids  to  assume 
their  constant  volume  at  the  standard  temperature.  If  the  strength 
of  a  standard  solution  is  known  for  one  temperature,  the  strength 
corresponding  to  another  temperature  can  only  be  calculated  if  the 
rate  of  expansion  by  heat  of  the  liquid  is  known.  The  variation 
cannot  be  estimated  by  the  known  rule  of  expansion  in  distilled 
water;  for  Gerlach  has  shown  that  even  weak  solutions  of  acids 
and  salts  expand  far  more  than  water  for  certain  increments  of 
temperature.  The  rate  of  expansion  for  pure  water  is  known, 
and  may  be  used  for  the  purpose  of  verifying  the  graduation  of 
instruments,  where  extreme  accuracy  is  required.  The  following 
short  table  furnishes  the  data  for  correction. 

The  weight  of  1000  c.c.  of  water  at  t°  C.,  when  determined  by 
means  of  brass  weights  in  air  of  t°  C.,  and  at  0*76  m.m.  pressure, 
is  equal  to  1000  -  x  gin. 

Slight  variations  of  atmospheric  pressure  may  be  entirely 
disregarded. 


t° 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

X 

1-34 

1-43 

1-52 

1-63 

1-76 

1-89 

2-04 

2-2 

2-37 

2-55 

t° 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

X 

2-74 

2-95 

317 

3-39 

3-63 

3-88 

4-13 

4-39 

4-67 

4-94 

5'24 

x  is  the  quantity  to  be  subtracted  from  1000  to  obtain  the 
weight  of  1000  c.c.  of  water  at  the  temperature  t°.  Thus  at  20° 
2-74  must  be  deducted  from  1000  =  997'26. 

Bearing  the  foregoing  remarks  in  mind,  therefore,  the  safest  plan 
in  the  operations  of  volumetric  analysis,  so  far  as  measurement  is 
concerned,  is  to  use  solutions  as  dilute  as  possible.  Absolute 
accuracy  in  estimating  the  strength  of  standard  solutions  can  only 


WEIGHTS   AND   MEASURES. 


21 


be  secured  by  weight,  the  ratio  of  the  weight  of  the  solution  to  the 
weight  of  active  substance  in  it  being  independent  of  temperature. 

Casamajor  (C.  N.  xxxv.  160)  has  made  use  of  the 
data  given  by  Matthiessen  in  his  researches  on  the  expansion 
of  glass,  water,  and  mercury,  to  construct  a  table  of  corrections  to 
be  used  in  case  of  using  any  weak  standard  solution  at  a  different 
temperature  to  that  at  which  it  was  originally  standardized. 

The  expansion  of  water  is  different  at  different  temperatures ; 
the  expansion  of  glass  is  known  to  be  constant  for  all  temperatures 
up  to  100°.  The  correction  of  volume,  therefore,  in  glass  burettes, 
must  be  the  known  expansion  of  each  c.c.  of  water  for  every  1°  C., 
less  the  known  expansion  of  glass  for  the  same  temperature. 

It  is  not  necessary  here  to  reproduce  the  entire  paper  of 
Casamajor,  but  the  results  are  shortly  given  in  the  following 
table. 

The  normal  temperature  is  15°  C.  ;  and  the  figures  given  are  the 
relative  contractions  below,  and  expansions  above,  15°  C. 


Deg.  C. 

7- 

•000612 

8  — 

•000590 

9  — 

•000550 

10  - 

•000492 

11  — 

•000420 

12  — 

•000334 

13  — 

•000236 

14  - 

•000124 

15 

Normal 

16  + 

•000147 

17  + 

•000305 

18  + 

•000473 

19  + 

•000652 

20  + 

•000841 

21  + 

•001039 

22  + 

•001246 

23  + 

•001462 

Deg.  C. 

24  + 

•001686 

25  + 

•001919 

26  + 

•002159 

27  + 

•002405 

28  + 

•002657 

29  + 

•002913 

30  + 

•003179 

31  + 

•003453 

32  + 

•003739 

33  + 

•004035 

34  + 

•004342 

35  + 

•004660 

36  + 

•004987 

37  + 

•005323 

38  + 

•005667 

39  + 

•006040 

40  + 

•006382 

By  means  of  these  numbers  it  is  easy  to  calculate  the  volume  of 
liquid  at  15°  C.  corresponding  to  any  volume  observed  at  any 
temperature.  If  35  c.c.  of  solution  has  been  used  at  37°  C.,  the 
table  shows  that  1  c.c.  of  water  in  passing  from  15°  to  37°  is 
increased  to  1  '005323  c.c. ;  therefore,  by  dividing  35  c.c.  by  1  '005323 
is  obtained  the  quotient  34 '8 19  c.c.,  which  represents  the  volume 
at  15°  corresponding  to  35  c.c.  at  37°;  or  the  operation  can  be 
simplified  by  obtaining  the  factor,  thus  : 


1-005323 


=  0-994705 


A  table   can  thus  be  easily  constructed  which  would  show  the 
factor  for  each  degree  of  temperature. 

These  corrections  are  useless  for  concentrated  solutions,  such  as 


22  VOLUMETRIC   ANALYSIS.  §    9. 

normal  alkalies  or  acids ;  with  great  variations  of  temperature 
these  solutions  should  be  used  by  weight. 

The  accurate  graduation  of  burettes  and  pipettes  can  only  be 
done  by  carefully  constructed  machines,  and  is,  therefore,  generally 
speaking,  beyond  the  compass  of  the  analyst  himself ;  nevertheless, 
they  should  be  carefully  tested  by  him  before  being  used,  as, 
unfortunately,  they  do  not  always  possess  the  accuracy  to  which 
they  pretend.  In  the  verification  of  both  burettes  and  pipettes,  it 
is  only  necessary  to  allow  ten  cubic  centimeters  of  distilled  water 
to  flow  from  the  instrument  to  be  tested  into  a  dry  and  accurately 
tared  flask  or  beaker.  If  the  weight  at  16°  C.,  or  60°  Fahr.,  is  10 
grams,  it  is  sufficient;  the  next  10  c.c.  may  be  tried  in  like 
manner,  and  so  on  until  the  entire  capacity  is  proved ;  differences 
of  5  or  10  milligrams  may  be  disregarded.  Thorpe  (Quant if. 
Chem.  Anal.  p.  119)  attaches  the  burette  or  pipette  with  elastic 
tube  and  pinch-cock  to  a  balance,  and  thus  weighs  the  respective 
volumes  of  fluid  delivered. 

Graduated  flasks  are  extremely  serviceable  in  dividing  small 
quantities  of  substance  into  still  smaller  proportional  parts. 
Suppose,  for  instance,  it  is  desired  to  take  the  tenth  part  of  a 
solution  for  the  purpose  of  separating  any  single  constituent,  let 
it  be  put  into  a  200  c.c.  flask,  which  is  then  filled  to  the  mark 
with  water  or  other  appropriate  liquid,  and  well  shaken;  20  c.c. 
taken  out  with  a  pipette  will  at  once  give  the  quantity  required. 

Instruments  graduated  on  the  Grain  System. — Burettes,  pipettes, 
and  flasks  may  also  be  graduated  in  grains,  in  which  case  it  is  best 
to  take  10,000  grains  as  the  standard  of  measurement.  In  order 
to  lessen  the  number  of  figures  used  in  the  grain  system,  so  far 
as  liquid  measures  are  concerned,  I  propose  that  ten  fluid  grains  be 
called  a  decem,  or  for  shortness  dm. ;  this  term  corresponds  to  the 
cubic  centimeter,  bearing  the  same  proportion  to  the  10,000  grain 
measure  as  the  cubic  centimeter  does  to  the  liter,  namely,  the 
one-thousandth  part.  The  use  of  a  term  like  this  will  serve  to 
prevent  the  number  of  figures,  which  are  unavoidably  introduced 
by  the  use  of  a  small  unit  like  the  grain. 

Its  utility  is  principally  apparent  in  the  analysis  for  percentages, 
particulars  of  which  will  be  found  hereafter. 

The  1000  grain  burette  or  pipette  will  therefore  contain  100 
decems,  the  10,000  gr.  measure  1000  dm.,  and  so  on. 

The  capacities  of  the  various  instruments  graduated  on  the  grain 
system  may  be  as  follows  : — 

Flasks  :  10000,  5000,  2500,  and  1000  grs.  =  1000,  500,  250,  and 
100  dm.  Burettes :  300  grs.  in  1-gr.  divisions,  for  very  delicate 
purposes  =  30  dm.  in  -^ ;  600  grs.  in  2-gr.  divisions,  or  \  dm.  ; 
1100  grs.  in  5-gr.  divisions,  or  -|  dm. ;  1100  grs.  in  10-gr.  divisions, 
or  1  dm.  The  burettes  are  graduated  above  the  500  or  1000  grs. 
in  order  to  allow  of  analysis  for  percentages  by  the  residual  method. 


§    10.  SYSTEMATIC    SOLUTIONS.  23 

Whole  pipettes  to  deliver  10,  20,  50,  100,  200,  500,  and  1000  grs., 
graduated  ditto,  100  grs.  in  -^  din.  ;  500  grs.  in  J  dm.  ;  1000  grs. 
in  1  dm. 

Those  who  may  desire  to  use  the  decimal  systems  constructed  on 
the  gallon  measure  =  70,000  grains,  will  bear  in  mind  that  the 
"septem"  of  Griffin,  or  the  "  decimillem  "  of  Ac  land  are  each 
equal  to  7  grs.,  ;  and  therefore  bear  the  same  relation  to  the 
pound  =  7000  grs.,  as  the  cubic  centimeter  does  to  the  liter,  or  the 
decem  to  the  10,000  grs.  An  entirely  different  set  of  tables  for 
calculations,  etc.,  is  required  for  these  systems;  but  the  analyst  may 
readily  construct  them  when  once  the  principles  contained  in  this 
treatise  are  understood. 

VOLUMETRIC  ANALYSIS  BASED  ON  THE  SYSTEM  OF 
CHEMICAL  EQUIVALENCE  AND  THE  PREPARATION 
OF  NORMAL  TITRATED  SOLUTIONS. 

§  10.  WHEN  analysis  by  measure  first  came  into  use,  the  test 
solutions  were  generally  prepared  so  that  each  substance  to  be  tested 
had  its  own  special  reagent;  and  the  strength  of  the  standard 
solution  was  so  calculated  as  to  give  the  result  in  percentages. 
Consequently,  in  alkalimetry,  a  distinct  standard  acid  was  used  for 
soda,  another  for  potash,  a  third  for  ammonia,  and  so  on,  necessi- 
tating a  great  variety  of  standard  solutions. 

Griffin  and  Ure  appear  to  have  been  the  first  to  suggest  the  use 
of  standard  test  solutions  based  on  the  atomic  system  ;  and  following 
in  their  steps,  Mohr  has  worked  out  and  verified  many  methods  of 
analysis,  which  are  of  great  value  to  all  who  concern  themselves 
with  scientific  and  especially  technical  chemistry.  Not  only  has 
Mohr  done  this,  but  in  addition  to  it,  he  has  enriched  his 
processes  with  so  many  original  investigations,  and  improved  the 
necessary  apparatus  to  such  an  extent,  that  he  may  with  justice 
be  called  the  father  of  the  volumetric  system. 

Normal  Solutions.  —  It  is  of  great  importance  that  no  misconcep- 
tion should  exist  as  to  what  is  meant  by  a  normal  solution  ;  but  it 
does  unfortunately  occur,  as  may  be  seen  by  reference  to  the 
chemical  journals,  also  to  Muir's  translation  of  Fleischer's 
book  (see  Allen,  C.  N.  xl.  239,  also  Analyst,  xiii.  181). 

Normal  solutions  as  originally  devised  are  prepared  so  that  one 
liter  at  16°  C.  shall  contain  the  hydrogen  equivalent  of  the  active 
reagent  weighed  in  grams  (H=l).  Seminormal,  quintinormal, 
decinormal,  and  centinormal  solutions  are  also  required,  and  may 
be  shortly  designated  as  |-  §  --$  and  TJy-  solutions.* 


*  It  is  much  to  be  regretted  that  the  term  "normal,"  originally  based  on  the 
equivalent  system,  should  now  be  appropriated  by  those  who  advocate  the  use  of 
solutions  based  on  molecular  weights,  because  it  not  only  leads  to  confusion  between 
the  two  systems,  but  to  utter  confusion  between  the  advocates  of  the  change 
themselves.  In  Fleischer's  German  edition  of  his  Maasanalijse  the  molecular  system 


24  VOLUMETRIC   ANALYSIS.  §    10. 

In  the  case  of  uiiivalent  substances,  such  as  silver,  iodine, 
hydrochloric  acid,  sodium,  etc.,  the  equivalent  and  the  atomic 
(or  in  the  case  of  salts,  molecular)  weights  are  identical ;  thus,  a 
normal  solution  of  hydrochloric  acid  must  contain  36 '37  grams  of 
the  acid  in  a  liter  of  fluid,  and  sodic  hydrate  40  grains.  In  the 
case  of  bivalent  substances,  such  as  lead,  calcium,  oxalic  acid, 
sulphurous  acid,  carbonates,  etc.,  the  equivalent  is  one-half  of  the 
atomic  (or  in  the  case  of  salts,  molecular)  weight ;  thus,  a  normal 
solution  of  oxalic  acid  would  be  made  by  dissolving  63  grams  of 
the  crystallized  acid  in  distilled  water,  and  diluting  the  liquid  to 
the  measure  of  one  liter. 

Further,  in  the  case  of  trivalent  substances,  such  as  phosphoric- 
acid,  a  normal  solution  of  sodic  phosphate  would  be  made  by 
weighing  -^f-=  119*3  grams  of  the  salt,  dissolving  in  distilled  water, 
and  diluting  to  the  measure  of  one  liter. 

One  important  point,  however,  must  not  be  forgotten,  namely, 
that  in  preparing  solutions  for  volumetric  analysis  the  value  of  a 
reagent  as  expressed  by  its  equivalent  hydrogen-weight  must  not 
always  be  regarded,  but  rather  its  particular  reaction  in  any  given 
analysis ;  for  instance,  tin  is  a  quadrivalent  metal,  but  when 
using  stannous  chloride  as  a  reducing  agent  in  the  analysis  of 
iron,  the  half,  and  not  the  fourth,  of  its  molecular  weight  is 
required,  as  is  shown  by  the  equation  Fe2  Cl°  +  Sn  Cl2  =  2  Fe  Cl2 
+  Sn  Cl4. 

In  the  same  manner  with  a  solution  of  potassic  permanganate 
Mn  KO4  when  used  as  an  oxidizing  agent,  it  is  the  available  oxygen 
which  has  to  be  taken  into  account,  and  hence  in  constructing  a 
normal  solution  one-fifth  of  its  molecular  weight  i?*-  =  31'6 
grams  must  be  contained  in  the  liter. 

Other  instances  of  a  like  kind  occur,  the  details  of  which  will 
be  given  in  the  proper  place. 

is  advocated,  but,  as  the  old  atomic  weights  are  used,  the  solutions  are  really,  in  the 
main,  of  the  same  strength  as  those  based  on  the  equivalent  system.  Pattinson 
Muir,  however,  in  his  translation,  has  thought  proper  to  use  modern  atomic  weights, 
and  the  curious  result  seems  that  one  is  directed  to  prepare  a  normal  solution  of 
caustic  potash  with  39'1  grams  K  to  the  liter,  while  a  normal  potassic  carbonate  is 
to  contain  138'2  grams  K2CO3,  or  78'2  grams  K,  in  the  same  volume  of  solution. 
Again,  Muter,  in  his  Manual  nf  Analytical  Chemistry,  defines  a  normal  solution  as 
having  one  molecular  weight  of  the  reagent  in  grams  per  liter ;  then  follows  the 
glaring  inconsistency,  among  others,  of  directing  that  a  decinormal  solution  of  iodine 
should  contain  127  grams  of  I  per  liter,  whereas,  if  it  was  strictly  made  according 
to  the  original  definition,  it  should  contain  25'4  grams  in  the  liter. 

If  the  unit  H  be  adopted  as  the  basis  or  standard,  everything  is  simplified,  and 
actual  normal  solutions  may  be  made  and  used ;  but,  on  the  molecular  system,  this 
is,  in  many  cases,  not  only  unadvisable  but  impossible,  besides  leading  to  ridiculous 
inconsistencies.  As  Allen  points  out  in  the  reference  above,  it  is,  to  say  the  least 
of  it,  highly  inconvenient  that  the  nomenclature  of  a  standard  solution  should  be 
capable  of  two  interpretations.  I  have  given  the  term  a;;stematic  to  this  handbook, 
and  I  maintain  that  the  equivalent  system  used  is  the  only  systematic  and  consistent 
one;  it  was  adopted  originally  by  Mohr,  followed  by  Fresenius,  and  continued 
by  Classen  in  the  new  edition  of  Mohr's  Titrii methode.  Allen  himself  has 
unhesitatingly  preferred  to  use  it  in  his  Organic  Analysis,  and  these,  together  with 
this  treatise,  being  all  text-books  having  a  wide  circulation,  ought  to  settle  definitely 
the  meaning  of  the  t<  rm  normal  as  applied  to  systematic  standard  solutions.  Anyhow, 
it  is  to  be  hoped  that  those  who  communicate  processes  to  the  chemical  journals,  or 
abstractors  of  foreign  ai  tides  for  publication,  will  take  care  to  distinguish  between 
the  conflicting  systems. 


§    10.  SYSTEMATIC   SOLUTIONS.  25 

A  further  illustration  may  be  given  in  order  to  show  the 
method  of  calculating  the  results  of  this  kind  of  analysis. 

Each  c.c.  of  Y^-  silver  solution  will  contain  y^^nr  of  the  atomic 
weight  of  silver  =  0*010766  gm.,  and  will  exactly  precipitate 
T_i.__  of  the  atomic  weight  of  chlorine  =  0*003537  gm.  from  any 
solution  of  a  chloride. 

In  the  case  of  normal  oxalic  acid  each  c.c.  will  contain  ^-^-5  of 
the  molecular  weight  of  the  acid  =  0*0 6 3  gm.,  and  will  neutralize 
__i__  of  the  molecular  weight  of  sodic  monocarbonate  =  0*053 
gm.,  or  will  combine  with  o-^Vo"  °f  the  atomic  weight  of  a 
dyad  metal  such  as  lead  =  0 '1032  gm.,  or  will  exactly  saturate 
__!__  of  the  molecular  weight  of  sodic  hydrate  =  0*040  gm.,  and 
so  on. 

Where  the  1000  grain  measure  is  used  as  the  standard  in  place  of 
the  liter,  63  grains  of  oxalic  acid  would  be  used  for  the  normal 
solution;  but  as  1000  grains  is  too  small  a  quantity  to  make,  it  is 
better  to  weigh  630  grains,  and  make  up  the  solution  to  10,000 
grain  measures  =  1000  dm.  The  solution  would  then  have  exactly 
the  same  strength  as  if  prepared  on  the  liter  system,  as  it  is  pro- 
portionately the  same  in  chemical  power ;  and  either  solution  may 
be  used  indiscriminately  for  instruments  graduated  on  either  scale, 
bearing- in  mind  that  the  substance  to  be  tested  with  a  c.c.  burette 
must  be  weighed  on  the  gram  system,  and  vice  versa,  unless  it 
be  desired  to  calculate  one  system  of  weights  into  the  other. 

The  great  convenience  of  this  equivalent  system  is,  that  the 
numbers  used  as  coefficients  for  calculation  in  any  analysis  are 
familiar,  and  the  solutions  agree  with  each  other,  volume  for 
volume.  We  have  hitherto,  however,  looked  only  at  one  side  of  its 
advantages.  For  technical  purposes  the  plan  allows  the  use  of 
all  solutions  of  systematic  strength,  and  simply  varies  the  amount 
of  substance  tested  .according  to  its  equivalent  weight. 

Thus,  the  normal  solutions  say,  are — 

Crystallized  oxalic  acid  =  63  gm.  per  liter. 

Sulphuric  acid  =49  gm.        ,, 

Hydrochloric  acid  =36.37  gm.  „ 

Nitric  acid  =63  gm.        ,, 
Anhydrous  sodic  carbonate       =53  gm.        ,, 

Sodic  hydrate  =40  gm.        ,, 

Ammonia  =17  gm.        ,, 

100  c.c.  of  any  one  of  these  normal  acids  should  exactly  neutralize 
100  c.c.  of  any  of  the  normal  alkalies,  or  the  corresponding  amount 
of  pure  substance  which  the  100  c.c.  contain.  In  commerce  we 
continually  meet  with  substances  used  in  manufactures  which  are 
not  pure,  and  it  is  necessary  to  know  how  much  pure  substance 
they  contain. 

Let  us  take,  for  instance,  refined  soda  ash  (sodic  carbonate).  If 
it  were  absolutely  pure,  5*3  gm.  of  it  should  require  exactly  100  c.c. 


26  VOLUMETRIC  ANALYSIS.  §    10. 

of  any  normal  acid  to  saturate  it.  If  we  therefore  weigh  that 
quantity,  dissolve  it  in  water,  and  deliver  into  the  mixture  the 
normal  acid  from  a  burette,  the  number  of  c.c.  required  to  saturate 
it  will  show  the  percentage  of  pure  sodic  carbonate  in  the  sample. 
Suppose  90  c.c.  are  required  =  90  %. 

Again — a  manufacturer  buys  common  oil  of  vitriol,  and  requires 
to  know  the  exact  percentage  of  pure  hydrated  acid  in  it ;  4*9  grams 
are  weighed,  diluted  with  water,  and  normal  alkali  delivered  in 
from  a  burette  till  saturated ;  the  number  of  c.c.  used  will  be  the 
percentage  of  real  acid.  Suppose  58 '5  c.c.  are  required  =  58 '5  %. 

On  the  grain  system,  in  the  same  way,  53  grains  of  the  sample  of 
soda  ash  would  require  90  dm.  of  normal  acid,  also  equal  to  90  %. 

Or,  suppose  the  analyst  desires  to  know  the  equivalent  percentage 
of  dry  caustic  soda,  free  and  combined,  contained  in  the  above 
sample  of  soda  ash,  without  calculating  it  from  the  carbonate  found 
as  above,  3'1  gm.  is  treated  as  before,  and  the  number  of  c.c 
required  is  the  percentage  of  sodic  oxide.  In  the  same  sample 
52 '6  c.c.  would  be  required  =  52 '6  per  cent,  of  sodic  oxide,  or  90 
per  cent,  of  sodic  carbonate. 

Method  for  percentage  of  Purity  in  Commercial  Substances. — The 
rules,  therefore,  for  obtaining  the  percentage  of  pure  substance  in 
any  commercial  article,  such  as  alkalies,  acids,  and  various  salts, 
by  means  of  systematic  normal  solutions  such  as  have  been 
described  are  these — 

1.  With  normal  solutions  ~  or  ^  (according  to  its  atomicity) 
of  the  molecular  weight  in  grams  of  the  substance  to  be  analyzed 
is  to  be  weighed  for  titration,  and  the  number  of  c.c.  required  to 
produce  the  desired  reaction  is  the  percentage  of  the  substance 
whose  atomic  weight  has  been  used. 

With  decinormal  solutions  yj-^  or  ^^  of  the  molecular  weight 
in  grams  is  taken,  and  the  number  of  c.c.  required  will,  in  like 
manner,  give  the  percentage. 

Where  the  grain  system  is  used  it  will  be  necessary,  in  the  case 
of  titrating  with  a  normal  solution,  to  weigh  the  whole  or  half  the 
molecular  weight  of  the  substance  in  grains,  and  the  number  of 
decems  required  will  be  the  percentage. 

With  decinormal  solutions,  y1^  or  -j^  of  the  molecular  weight  in 
grains  is  taken,  and  the  number  of  decems  will  be  the  percentage. 

It  now  only  remains  k)  say,  with  respect  to  the  system  of  weights 
and  measures  to  be  used,  that  the  analyst  is  at  liberty  to  choose  his 
own  plan.  Both  systems  are  susceptible  of  equal  accuracy,  and  he 
must  study  his  own  convenience  as  to  which  he  will  adopt.  The 
normal  solutions  prepared  on  the  gram  system  are  equally  applicable 
for  that  of  the  grain,  and  vice  verm,  so  that  there  is  no  necessity 
for  having  distinct  solutions  for  each  system. 

Factors,  or  Coefficients,  for  the  Calculation  of  Analyses. — It 
frequently  occurs  that  from  the  nature  of  the  substance,  or  from 


§    10.  PRESERVATION   OF   SOLUTIONS.  27 

its  being  in  solution,  this  percentage  method  cannot  be  conveniently 
followed.  For  instance,  suppose  the  operator  has  a  solution  con- 
taining an  unknown  quantity  of  caustic  potash,  the  strength  of 
which  he  desires  to  know  ;  a  weighed  or  measured  quantity  of  it 
is  brought  under  the  acid  burette  and  exactly  saturated,  32  c.c. 
being  required.  The  calculation  is  as  follows  :  — 

The  molecular  weight  of  potassic  hydrate  being  56  :  100  c.c.  of 
normal  acid  will  saturate  5*6  gm.  ;  therefore,  as  100  c.c.  are  to  5*6  gm., 

so  are  32  c.c.  to  g,5'32  =  1*792  gm.  KHO. 


The  simplest  way,  therefore,  to  proceed,  is  to  multiply  the 
number  of  c.c.  of  test  solution  required  in  any  analysis,  by  the 
IFDTT  (or  T^Vo  ^  bivalent)  of  the  molecular  weight  of  the  substance 
sought,  which  gives  at  once  the  amount  of  substance  present. 

An  example  may  be  given  —  1  gm.  of  marble  or  limestone  is 
taken  for  the  estimation  of  pure  calcic  carbonate,  and  exactly 
saturated  with  standard  nitric  or  hydrochloric  acid  —  (sulphuric  or 
oxalic  acid  are,  of  course,  not  admissible)  17  '5  c.c.  are  required, 
therefore  17  "5  x  O'OSO  (the  TT^QO"  °f  the  molecular  weight  of 
CaCO3)  gives  0*875  gm.,  and  as  1  gm.  of  substance  only  wras 
taken  =  87  '5%  calcic  carbonate. 

Preservation  of  Solutions.  —  There  are  test  solutions  which,  in 
consequence  of  their  proneness  to  decomposition,  cannot  be  kept 
at  any  particular  strength  for  a  length  of  time  ;  consequently  they 
must  be  titrated  on  every  occasion  before  being  used.  Stannous 
chloride  and  sulphurous  acids  are  examples  of  such  solutions. 
Special  vessels  have  been  devised  for  keeping  solutions  liable  to 
alter  in  strength  by  access  of  air,  as  shown  in  figs.  20  and  21. 

Fig.  20  is  especially  applicable  to  caustic  alkaline  solutions,  the 
tube  passing  through  the  caoutchouc  stopper  being  filled  with  dry 
soda-lime,  resting  on  cotton  wool. 

Fig.  21,  designed  by  Mohr,  is  a  considerable  improvement 
upon  this,  since  it  allows  of  the  burette  being  filled  with  the 
solution  from  the  store  bottle  quietly,  and  without  any  access  of 
air  whatever.  The  vessel  can  be  used  for  caustic  alkalies,  baryta, 
stannous  chloride,  permanganate,  and  sulphurous  acids,  or  any  other 
liquid  liable  to  undergo  change  by  absorbing  oxygen.  The  corks 
are  dried  and  soaked  in  melted  paraffine  ;  or,  still  better,  may  be 
substituted  by  caoutchouc  stoppers  ;  and  a  thin  layer  of  rectified 
paraffin  oil  is  poured  on  the  top  of  the  solution,  where,  of  course, 
owing  to  its  low  specific  gravity,  it  always  floats,  placing  an 
impermeable  division  between  the  air  and  the  solution  ;  and  as 
this  body  (which  should  always  be  as  pure  as  possible)  is  not 
affected  by  these  reagents  in  their  diluted  state,  this  form  offers 
great  advantages.  Solutions  not  affected  chemically  by  contact 
with  air  should  nevertheless  be  kept  in  bottles,  the  corks  or  stoppers 
of  which  are  perfectly  closed,  and  tied  over  with  india-rubber  or 


28 


VOLUMETRIC  ANALYSIS. 


§    11. 


bladder  to  prevent  evaporation,  and  should  further  be  always 
shaken  before  use,  in  case  they  are  not  quite  full.  The  influence 
of  bright  light  upon  some  solutions  is  very  detrimental  to  their 


Fig.  21. 


chemical  stability ;  hence  it  is  advisable  to  preserve  some  solutions 
not  in  immediate  use  in  the  dark,  and  at  a  temperature  not 
exceeding  15  or  16°  C. 

ON    THE    DIRECT    AND    INDIRECT    PROCESSES    OF 
ANALYSIS  AND  THEIR  TERMINATION. 

§  11.  THE  direct  method  includes  all  those  analyses  where  the 
substance  under  examination  is  decomposed  by  simple  contact  with 
a  known  quantity  or  equivalent  proportion  of  some  other  body 
capable  of  combining  with  it,  and  where  the  end  of  the  decomposition 
is  manifested  in  the  solution  itself. 

It  also  properly  includes  those  analyses  in  which  the  substance 
reacts  upon  another  body  to  the  expulsion  of  a  representative 
equivalent  of  the  latter,  which  is  then  estimated  as  a  substitute 
for  the  thing  required. 


§    11.  DIRECT   AND   INDIRECT   METHODS.  29 

Examples  of  this  method  are  readily  found  in  the  process  for 
the  determination  of  iron  by  potassic  permanganate,  where  the 
beautiful  rose  colour  of  the  permanganate  asserts  itself  as  the  end 
of  the  reaction. 

The  testing  of  acids  and  alkalies  conies,  also,  under  this  class,  the 
great  sensitiveness  of  litmus,  or  other  indicators,  allowing  the 
most  trifling  excess  of  acid  or  alkali  to  alter  their  colour. 

The  indirect  method  is  exemplified  in  the  analysis  of  manganese 
ores,  and  also  other  peroxides  and  oxygen  acids,  by  boiling  with 
hydrochloric  acid.  The  chlorine  evolved  is  estimated  as  the 
equivalent  of  the  quantity  of  oxygen  which  has  displaced  it.  We 
are  indebted  to  Buns  en  for  a  most  accurate  and  valuable  series  of 
processes  based  on  this  principle. 

The  residual  method  is  such  that  the  substance  to  be  analyzed  is 
not  estimated  itself,  but  the  excess  of  some  other  body  added  for 
the  purpose  of  combining  with  it  or  of  decomposing  it ;  and  the 
quantity  or  strength  of  the  body  added  being  known,  and  the  con 
ditions  under  which  it  enters  into  combination  being  also  known, 
by  deducting  the  remainder  or  excess  (which  exists  free)  from  the 
original  quantity,  it  gives  at  once  the  proportional  quantity  of  the 
substance  sought. 

An  example  will  make  the  principle  obvious  : — Suppose  that  a 
sample  of  native  calcic  or  baric  carbonate  is  to  be  tested.  It  is  not 
possible  to  estimate  it  with  standard  nitric  or  hydrochloric  acid  in 
the  exact  quantity  it  requires  for  decomposition.  There  must  be 
an  excess  of  acid  and  heat  applied  also  to  get  it  into  solution ;  if, 
therefore,  a  known  excessive  quantity  of  standard  acid  be  first 
added,  and  solution  obtained,  and  the  liquid  then  titrated  backward 
with  an  indicator  and  standard  alkali,  the  quantity  of  free  acid  can 
be  exactly  determined,  and  consequently  that  which  is  combined 
also. 

In  some  analyses  it  is  necessary  to  add  a  substance  which  shall 
be  an  indicator  of  the  end  of  the  process ;  such,  for  instance,  is 
litmus  or  the  azo  colours  in  alkalimetry,  potassic  chromate  in  silver 
and  chlorine,  and  starch  in  iodine  estimations. 

There  are  other  processes,  the  end  of  which  can  only  be 
determined  by  an  indicator  separate  from  the  solution ;  such  is 
the  case  in  the  estimation  of  iron  by  potassic  bichromate,  where 
a  drop  of  the  liquid  is  brought  into  contact  with  another  drop  of 
solution  of  red  potassic  prussiate  on  a  white  slab  or  plate ;  when 
a  blue  colour  ceases  to  form  by  contact  of  the  two  liquids,  the  end 
of  the  process  is  reached. 


30 


VOLUMETRIC   ANALYSIS. 


12. 


PART    II. 
ANALYSIS   BY   SATURATION. 

ALKALIMETRY. 

§  12.  GAY  LUSSAC  based  his  system  of  alkalimetry  upon  -a 
titrated  solution  of  sodie  carbonate,  Avith  a  corresponding  solution 
of  sulphuric  acid.  It  possesses  the  recommendation,  that  a  pure 
standard  solution  of  sodic  carbonate  can  be  more  readily  obtained 
than  any  other  form  of  alkali.  Mohr  introduced  the  use  of 
caustic  alkali  instead  of  a  carbonate,  the  strength  of  which  is 
established  by  a  standard  solution  of  oxalic  or  sulphuric  acid. 
The  advantage  in  the  latter  system  is,  that  in  titrating  acids  with 
a  caustic  alkali,  the  well-known  interference  produced  in  litmus 
by  carbonic  acid  is  avoided :  this  difficulty  is  now  overcome  with 
carbonates  by  the  new  indicators  to  be  described. 


INDICATORS    USED    IN 
ALKALIMETRY. 

§  1 3.  1 .  Litmus  Solution. — This  well- 
known,  indicator  is  best  prepared  as 
follows  : — Extract  all  soluble  matters 
from  the  solid  litmus  by  repeated 
quantities  of  hot  water;  evaporate  the 
mixed  extracts  to  a  moderate  bulk,  and 
add  acetic  acid  in  slight  excess  to  de- 
compose carbonates ;  evaporate  to  a 
thick  extract,  transfer  this  to  a  beaker, 
and  add  a  large  proportion  of  hot  85- 
per-cent.  alcohol  or  methylated  spirit : 
by  this  treatment  the  blue  colour  is 
precipitated,  and  the  alkaline  acetates, 
together  with  some  red  colouring  matter, 
remain  dissolved ;  the  fluid  with  pre- 
cipitate is  thrown  on  a  filter,  washed 
with  hot  spirit,  and  the  pure  colouring 
Fig.  22.  matter  finally  dissolved  in  warm  distilled 

water,  through  the  filter,  for  use."* 

Another  method  gives  very  good  results.     The  crushed  litmus  is 

extracted  with  boiling  methylated  spirit,  three  or  four  times,  to 

*  It  is  preferable  to  keep  the  pasty  extract,  still  wet  with  spirit,  in  a  bottle,  and 
dissolve  a  little  in  warm  water  when  required,  adjusting  the  tint  with  very  dilute 
hydrochloric  acid  or  soda  as  the  case  may  be.  It  has  been  recommended  by  some  to 
dissolve  the  extract  in  glycerol,as  a  preservative,  but  the  use  of  any  foreign  matter  for 
this  purpose,  such  as  alcohol,  boric  or  salicylic  acid,  &c.,  ought  to  be  avoided. 


§    13.  INDICATORS.  31 

remove  the  red  colouring  matter,  the  residue  is  digested  for  some 
time  with  cold  water,  allowed  to  settle,  the  clear  liquid  decanted, 
acidified  with  sulphuric  acid  and  boiled  to  expel  CO2.  It  is  then 
cautiously  neutralized  with  baryta  water,  and  either  filtered  or 
allowed  to  settle  clear  for  use.  Unless  a  solution  of  litmus  has 
been  sterilized  by  mercuric  chloride,  or  some  such  agent,  it  speedily 
loses  its  colour  when  kept  in  closed  bottles,  becomes  offensive  in 
smell,  and  a  rapid  fungoid  growth  occurs,  due  to  a  micrococcus.  If 
kept  in  a  vessel  open  to  the  air,  such  as  is  shown  in  fig.  22,  the 
tendency  to  this  change  is  much  lessened,  and  whenever  the  colour 
may  have  been  lost,  it  can  be  restored  by  exposing  the  solution  to 
the  air  in  an  open  dish. 

Free  carbonic  acid  interferes  considerably  with  the  production  of 
the  blue  colour,  and  its  interference  in  titrating  acid  solutions  with 
alkaline  carbonates  can  only  be  got  rid  of  by  boiling  the  liquid 
during  the  operation,  in  order  to  displace  the  gas  from  the  solution. 
If  this  is  not  done,  it  is  easy  to  overstep  the  exact  point  of  neutrality 
in  endeavouring  to  produce  the  blue  colour.  The  same  difficulty  is 
also  found  in  obtaining  the  pink-red  when  acids  are  used  for 
titrating  alkaline  carbonates,  hence  the  great  value  of  the  caustic 
alkaline  solutions  free  from  carbonic  acid  when  this  indicator  is 
used. 

It  sometimes  occurs  that  titration  by  litmus  is  required  at  night. 
Ordinary  gas  or  lamp  light  is  not  adapted  for  showing  the  reaction 
in  a  satisfactory  manner;  but  a  very  sharp  line  of  demarcation 
between  red  and  blue  may  be  found  by  using  a  monochromatic 
light.  With  the  yellow  sodium  flanue  the  red  colour  appears 
perfectly  colourless,  while  the  blue  or  violet  appears  like  a  mixture 
of  black  ink  and  water.  The  transition  is  very  sudden,  and  even 
sharper  than  the  change  by  daylight. 

The  operation  should  be  conducted  in  a  perfectly  dark  room ; 
and  the  flame  may  be  best  obtained  by  heating  a  piece  of  platinum 
coil  sprinkled  with  salt,  or  a  piece  of  pumice  saturated  with  a 
concentrated  solution  of  salt,  in  the  Bunsen  flame. 

2.  Litmus   Paper. — Is    simply    made    by    dipping    strips    of 
calendered  unsized  paper  in  the  solution  and  drying  them ;   the 
solution   used    being   rendered    blue,    red,    or   violet   as   may   be 
required. 

3.  Cochineal  Solution. — This  indicator  possesses  the  advantage 
over  litmus,  that  it  is  not  so  much  modified  in  colour  by  the  presence 
of  carbonic  acid,  and  can  be  used  by  gas-light.     It  can  also  IDC  used 
with  the  best  effect  with  solutions  of  the  alkaline  earths,  such  as 
lime  and  baryta  water ;  the  colour  with  pure  alkalies  and  earths  is 
especially  sharp  and  brilliant.     The  solution  is  made  by  digesting 
1  part  of  crashed  cochineal  with  10  parts  of  25-per-cent.  alcohol. 
Its  natural  colour  is  yelloAvish-red,  which  is  turned  to  violet  by. 
alkalies;   mineral  acids  restore  the  original  colour;   it  is  not  so 


32  VOLUMETRIC    ANALYSIS.  §18. 

easily  affected  by  weak  organic  acids  as  litmus,  and  therefore  for 
these  acids  the  latter  is  preferable.  It  cannot  be  used  in  the  pre- 
sence of  even  traces  of  iron  or  alumina  compounds  or  acetates, 
which  fact  greatly  limits  its  use. 

4.  Turmeric  Paper.  —  Pettenkofer,  in  his  estimation  of  car- 
bonic acid  by  baryta  water,  prefers  turmeric  paper  as  an  indicator. 
For  this  purpose  it  is  best  prepared  by  digesting  pieces  of  the  root, 
first  in  repeated  small  quantities  of  water  to  remove  a  portion  of 
objectionable  colouring  matter,  then  in  alcohol,  and  dipping  strips 
of  calendered  unsized  paper  into  the  alcoholic  solution,  drying  and 
preserving  them  in  the  dark. 

Thompson  in  continuance  of  his  valuable  studies  on  various 
indicators  found  that  turmeric  paper  is  of  very  little  use  for 
ammonia,  or  the  alkaline  carbonates,  or  sulphides  and  sulphites, 
but  he  prepared  a  special  paper  of  a  light  red-brown  colour,  by 
dipping  it  into  the  alcoholic  tincture  of  turmeric  rendered  slightly 
alkaline  by  caustic  soda.  If  this  paper  is  wetted  with  water  the 
eolour  is  intensified  to  a  dark  red-brown  ;  when  partly  immersed  in 
a  very  dilute  solution  of  an  acid,  the  wetted  portion  becomes  bright 
yellow,  while  immediately  above  this  a  moistened  dark  red-brown 
band  is  formed,  and  the  upper  dry  portion  retains  its  original 
colour.  This  appearance  only  occurs  in  the  titration  of  a  com- 
paratively large  proportion  of  an  acid,  when  the  latter  is  nearly  all 
neutralized,  and  thus  serves  to  indicate  the  near  approach  to  the 
end-reaction.  When  neutral  or  alkaline,  the  colour  of  the  immersed 
portion  of  paper  is  simply  intensified  as  already  described.  This 
intensification  is  quite  as  decided  as  a  change  of  tint.  This  red- 
brown  paper  is  equally  as  sensitive  as  phenolphthalein  for  the 
titration  of  citric,  acetic,  tartaric,  oxalic  and  other  organic  acids  by 
standard  soda  or  potash,  and  can  be  used  for  highly  coloured 
solutions.  It  is  also  available,  like  phenolphthalein,  for  the 
estimation  of  small  quantities  of  acid  in  strong  alcohol. 


Indicators  derived  from  the  Azo  Colours,  etc. 

An  immense  stride  has  been  taken  in  the  application  of  these 
modern  indicators,  and  the  best  thanks  of  all  chemists  are  due  to 
E.  T.  Thompson  for  his  valuable  researches  on  them,  read  before 
the  Chemical  Section  of  the  Philosophical  Society  of  Glasgow,  and 
published  in  their  Transactions;  also  reprinted  (C.  N.  xlvii.  123, 
185;  xlix.  32,  119;  J.  S.  C.  I.  vi.  195).  The  experiments 
recorded  in  these  papers  are  most  carefully  carried  out,  and  the 
truthfulness  of  their  results  has  been  verified  by  Lunge  and  other 
practical  men  as  well  as  by  myself. 

Space  will  only  permit  here  of  a  record  of  the  results,  fuller 
details  being  given  in  the  publications  to  which  reference  has  been 
made. 


§    13.  INDICATORS.  33 

5.  Methyl  Orange,  or  para-sulpho-benzene  azo-dimethylaniline, 
is  prepared  by  the  action  of  diazotized  sulphanilic  acid  upon 
dimethylaniline,  the  commercial  product  being  an  ammonium  or 
sodium  salt  of  the  sulphonic  acid  thus  produced.  If  carefully 
prepared  from  the  purest  materials  it  possesses  a  bright  orange 
colour,  perfectly  soluble  in  water ;  but  the  commercial  product  is 
a  powder  possessing  a  dull  orange-brown  appearance,  probably  due 
to  slight  impurities  in  the  substances  from  which  it  is  produced, 
and  often  not  completely  soluble  in  water.  Complaints  have  been 
made  by  some  operators  that  the  commercial  article  is  sometimes 
unreliable  as  an  indicator;  it  may  be  so,  but  although  I  have 
examined  many  specimens,  I  have  not  yet  found  any  in  which 
the  impurities  sensibly  affected  its  delicate  action  when  used  in 
the  proper  manner.  The  common  error  is  the  use  of  too  much 
of  it;  again,  there  is  the  personal  error  of  observation,  some 
eyes  being  much  more  sensitive  to  the  change  of  tint  than  others. 
The  great  value  of  this  indicator  is  that,  unlike  litmus  and  some 
other  agents,  it  is  totally  unaffected  by  carbonic  acid,  sulphuretted 
hydrogen,  hydrocyanic,  silicic,  boric,  arsenious,  oleic,  stearic, 
palmitic,  and  carbolic  acids,  etc.  It  must  not  be  used  for  the 
organic  acids,  such  as  oxalic,  acetic,  citric,  tartaric,  etc.,  since  the 
end-reaction  is  indefinite ;  nor  can  it  be  used  in  the  presence  of 
nitrous  acid  or  nitrites,  which  decompose  it.  It  may  safely  be 
used  for  the  estimation  of  free  mineral  acids  in  alum,  ferrous 
sulphate  or  chloride,  zinc  sulphate,  cupric  sulphate  or  chloride. 
The  acid  radical  (and  consequently  its  equivalent  metal)  in  cupric 
sulphate  and  similar  salbs  may  be  estimated  with  accuracy  by 
precipitating  the  solution  with  sulphuretted  hydrogen,  filtering, 
and  titrating  the  filtrate  at  once  with  normal  alkali  and  methyl 
orange.  The  earthy  carbonates  dissolved  in  natural  waters  (and 
which  constitute  the  temporary  hardness)  may  immediately  be 
estimated  by  simple  titration  with  ~  mineral  acid  and  this 
indicator. 

Nothing  can  exceed  the  value  of  methyl  orange  for  the  accurate 
standardizing  of  any  of  the  mineral  acids  by  means  of  pure  sodic 
carbonate  in  the  cold,  the  liberated  carbonic  acid  having  practically 
no  effect,  as  is  the  case  with  many  indicators.  Its  effect  is  also 
admirable  with  ammonia  or  its  salts.  A  convenient  strength  for 
the  indicator  is  1  gram  of  the  powder  in  a  liter  of  distilled  water ; 
a  single  drop  of  the  liquid  is  sufficient  for  100  c.c.  or  more  of  any 
colourless  solution — the  colour  being  faint  yellow  if  alkaline,  and 
pink  if  acid ;  if  too  much  is  used  the  end-reaction  is  slower  and 
less  definite.  All  titrations  with  methyl  orange  should  be  carried 
on  at  ordinary  temperatures. 

There  are  two  other  azo-compounds  in  use,  more  especially  by 
continental  chemists,  which  possess  the  same  properties  and  give 
much  the  same  effect  as  methyl  orange,  namely,  Fischer's 
dimethylamido-azobenzene  and  trop03olin  00.  My  experience  is 


34  VOLUMETEIC  ANALYSIS.  §    13. 

that  these  preparations  are  less  sensitive  than  methyl  orange,  and 
wherever  they  are  recommended  for  any  process  of  titration  the 
latter  may  be  substituted  with  advantage. 

6.  Phenacetolin. — This  substance  is  prepared  by  boiling  together 
for  several  hours  equal  molecular   proportions  of   phenol,   acetic 
anhydride,  and  sulphuric  acid.     The  product  is  well  washed  with 
water  to  remove  excess  of   acid  and  dried  for  use ;  it  is  soluble 
only  in  alcohol,  and  a  convenient  strength  is  2  gm.  per  liter.     The 
solution  is  dark  brown,  which  gives  a  scarcely  perceptible  yellow 
Avith  caustic  soda  or  potash,  when  a  few  drops  are  used  with  the 
ordinary   volumes    of   liquid.      With   ammonia   and    the   normal 
alkaline  carbonates  it  gives  a  dark  pink,  with  bicarbonate  a  much 
more  intense  pink,  and  with  mineral  acids  a  golden  yellow.     This 
indicator  may  be  used  to  estimate  the  amount  of  caustic  potash 
or  soda  in  the  presence  of  their  normal  carbonates  if  the  proportion 
of  the  former  is  not  very  small,  or  of  caustic  lime  in  the  presence 
of  carbonate. 

Practice  however  is  required  with  solutions  of  known  composition, 
so  as  to  acquire  knowledge  of  the  exact  shades  of  colour. 

7.  Phenolphthalein. — This   substance   is   obtained   by  heating 
together  at  120°  C.,  for  ten  or  twelve  hours,  five  parts  of  phthalic 
anhydride,  ten  of  phenol,  and  four  of  sulphuric  acid ;  the  product 
is  boiled  with  water,  and  the  residue  dissolved  in  dilute  soda  and 
filtered.      The  filtrate  contains   the  phenolphthalein,  which  may 
be  precipitated  by  neutralizing  with  acetic  and  hydrochloric  acids, 
and  purified  by  solution  in  alcohol,  boiling  with  animal  charcoal 
and  re-precipitating  with  boiling  water ;  it  is  of  a  resinous  nature, 
but  quite  soluble  in  50-per-cent.  alcohol.     A  convenient  strength 
is  5  gm.  per  liter. 

A  few  drops  of  the  indicator  show  no  colour  in  the  ordinary 
volumes  of  neutral  or  acid  liquids ;  the  faintest  excess  of  caustic 
alkalies,  on  the  other  hand,  gives  a  sudden  change  to  purple-red. 

This  indicator  is  useless  for  the  titration  of  free  ammonia,  or  its 
compounds,  or  for  the  fixed  alkalies  when  salts  of  ammonia  are 
present.*  It  is  also  very  easily  affected  by  CO2  and  SH2. 

It  may  however  be  used  like  phenacetolin  for  estimating  the 
proportions  of  hydrate  and  carbonate  of  soda  or  potasli  in  the 
same  sample  where  the  proportion  of  hydrate  is  not  too  small. 
Unlike  methyl  orange,  this  indicator  is  especially  useful  in  titrating 
all  varieties  of  organic  acids;  viz.,  oxalic,  acetic,  citric,  tartaric, 
etc. 

One  great  advantage  possessed  by  phenolphthalein  is,  that  it 
may  be  used  in  alcoholic  solutions,  or  mixtures  of  alcohol  and 

*  Long  (Artier.  Chem.  Jour,  xi,  84)  states,  and  my  own  experiments  support  him,  that 
this  disadvantage  may  he  remedied  in  many  cases  hy  using  a  large  proportion  of  the 
indicator  and  a  low  temperature. 


§    13.  INDICATOKS.  35 

ether,*  and  therefore  many  organic  acids  insoluble  in  water  may 
be  accurately  titrated  by  its  help ;  in  addition  to  this  it  may  be 
used  to  estimate  the  acid  combined  with  many  organic  bases, 
such  as  morphia,  quinia,  brucia,  etc.,  the  base  having  no  effect 
on  the  indicator. 

8.  Rosolic  Acid,  also  known  as  Aurin  or  Corallin,  is    soluble 
in  50-per-cent  alcohol,  and  a  convenient  strength  is  2  gm.  per  liter. 
Its  colour  is  pale  yellow,  unaffected  by  acids,  but  turning  to  violet- 
red  with  alkalies.     It  possesses  the  advantage  over  litmus  and  the 
other  indicators,  that  it  can  be  relied  upon  for  the  neutralization  of 
.sulphurous  acid  with  ammonium  to  normal  sulphite  (Thompson). 
Its  delicacy  is  sensibly  affected  by  salts  of  ammonia  and  by  carbonic 
acid.     It  is  excellent  for  all  the  mineral,  but  not  reliable  for  the 
organic  acids,  excepting  oxalic. 

9.  Lacmoid. — This  indicator  is  a  product 'of  resorcin,  and  is 
therefore  somewhat  allied  to  litmus  ;  nevertheless,  it  differs  from  it 
in  many  respects,  and  has  a  pronounced  and  valuable  character  of 
its  own,  especially  when  used  in  the  form  of  paper.     It  may  be 
prepared  by  heating  gradually  to  110°  C.  a  mixture  of  100  parts 
resorcin,  five  parts  sodic  nitrite,  and  five  parts  water ;  after  the 
violent  reaction  moderates,  it  is  heated  to  120°  C.  until  evolution 
of  ammonia  ceases.     The  residue  is  dissolved  in  warm  water,  and 
the   lacmoid   precipitated   therefrom  by  hydrochloric  acid;   it  is 
well  washed  from  free  acid  and  dried  for  use.     Lacmoid  is  soluble 
in  dilute  alcohol,  and  the  indicator  is  best  made  by  dissolving 
2  gm.  to  the  liter. 

10.  Lacmoid  Paper. — This    is    prepared    by   dipping   slips    of 
calendered  unsized  paper  into  the  blue  or  red  solution,  and  drying 
them. 

Thompson  states  that,  in  nearly  every  particular,  lacmoid  paper, 
either  blue  or  red,  is  an  excellent  substitute  for  methyl  orange, 
and  may  be  employed  in  titrating  coloured  solutions  where  the 
latter  would  be  useless.  Solution  of  lacmoid,  on  the  other  hand, 
is  not  so  valuable  as  the  paper,  inasmuch  as  it  is  more  easily  affected 
by  weak  acids  such  as  carbonic,  boric,  etc. 

There  are  a  host  of  other  indicators  belonging  to  the  same  category 
as  those  mentioned  above,  such  as  Congo  red,  Porrier's  blue, 
nuorescin,  etc. ;  but  as  they  have  no  special  advantages  over  them, 
and  indeed  are  practically  inferior  in  delicacy,  no  description  of 
them  will  be  given  here. 

*  H.  N.  and  C.  Draper  (C.  N.  lv.  143)  have  shown  that  this  indicator  is  rapidly 
decomposed  by  atmospheric  carbonic  acid,  which  is  more  readily  absorbed  by  alcohol 
than  by  water.  Fortunately  thig  is  less  the  case  with  hot  solutions  than  with  cold  ; 
titrations  of  this  kind  should  therefore  be  quickly  done,  and  with  not  too  small  a 
quantity  of  the  indicator. 

D    2 


36  VOLUMETRIC   ANALYSIS.  §    13. 

Special  indicators  for  certain  purposes,  such  as  potassic  chromate 
for  silver,  ferric  sulphate  for  sulphocyanides,  etc.,  will  be  described 
in  their  proper  place. 


SHORT  SUMMARY  OF  THOMPSON'S  RESULTS  WITH 
INDICATORS  AND  PURE  SALTS  OF  THE  ALKALIES 
AND  ALKALINE  EARTHS. 

The  whole  of  the  base  or  acid  in  the  following  list  of  substances 
may  be  estimated  with  delicacy  and  precision  unless  otherwise 
mentioned. 

Litmus  Cold. — Hydrates  of  soda,  potash,  ammonia,  lime,  baryta, 
etc.  ;  arsenites  of  soda  and  potash,  and  silicates  of  the  same  bases ; 
nitric,  sulphuric,  hydrochloric,  and  oxalic  acids. 

Litmus  Boiling. — The  neutral  and  acid  carbonates  of  potash, 
soda,  lime,  baryta,  and  magnesia,  the  sulphides  of  sodium  and 
potassium,  and  the  silicates  of  the  same  bases. 

Methyl  Orange  Cold. — The  hydrates,  carbonates,  bicarbonates, 
sulphides,  arsenites,  silicates,  ancl  borates  of  soda,  potash,  ammonia, 
lime,  magnesia,  baryta,  etc.,  all  the  mineral  acids,  sulphites,  half  the 
base  in  the  alkaline  and  earthy  alkaline  phosphates  and  arseniates. 

Rosolic  Acid  Cold. — The  whole  of  the  base  or  acid  may  be 
estimated  in  the  hydrates  of  potash,  soda,  ammonia,  and  arsenites 
of  the  same  ;  the  mineral  and  oxalic  acids. 

Rosolic  Acid  Boiling. — The  alkaline  and  earthy  hydrates  and 
carbonates,  bicarbonates,  sulphides,  arsenites,  and  silicates. 

Phenacetolin  Cold. — The  hydrates,  arsenites,  and  silicates  of  the 
alkalies ;  the  mineral  acids. 

Phenacetolin  Boiling. — The  alkaline  and  earthy  hydrates,  car- 
bonates, bicarbonates,  sulphides,  arsenites,  and  silicates. 

Phenolphthalein  Cold. — The  alkaline  hydrates,  except  ammonia ; 
the  mineral  acids,  oxalic,  citric,  tartaric,  acetic,  and  other  organic 
acids. 

Phenolphthalein  Boiling. — The  alkaline  and  earthy  hydrates, 
carbonates,  bicarbonates,  and  sulphides,  always  excepting  ammonia 
and  its  salts. 

Lacmoid  Cold. — The  alkaline  and  earthy  hydrates,  arsenites  and 
borates,  and  the  mineral  acids.  Many  salts  of  the  metals  which  are 


§    13.  INDICATORS.  37 

more  or  less  acid  to  litmus  are  neutral  to  lacmoid,  sucli  as  the 
sulphates  and  chlorides  of  iron,  copper,  and  zinc ;  therefore  this 
indicator  serves  for  estimating  free  acids  in  such  solutions. 

Lacmoid  Boiling-. — The  hydrates,  carbonates,  and  bicarbonates  of 
potash,  soda,  and  alkaline  earths. 

Lacmoid  Paper. — The  alkaline  and  earthy  hydrates,  carbonates, 
bicarbonates,  sulphides,  arsenites,  silicates,  and  borates  ;  the  mineral 
acids ;  half  of  the  base  in  sulphites,  phosphates,  arseniates. 

This  indicator  re-acts  alkaline  with  the  chromates  of  potash  or 
soda,  but  neutral  with  the  bichromates,  so  that  a  mixture  of  the 
two,  or  of  bichromates  with  free  chromic  acid,  may  be  titrated  by 
its  aid,  which  could  also  be  done  with  methyl  orange  were  it  not 
for  the  colour  of  the  solutions. 

The  following  substances  can  be  determined  by  standard 
alcoholic  potash,  with  phenolphthalein.  as  indicator.  One  c.c. 
normal  caustic  potash  (1  c.c.  =  '056  gm.  KHO)  is  equal  to — 
(Hehner  and  Allen) 


•088  gn 
•282     , 
•256     , 
•284     , 
•410     , 
•329     , 

i.    butyric  acid.          '1007  gm.    tributyrin. 
oleic  acid.              '2947     „      triolein. 
palmitic  acid.        '2687     „      tripalmitin. 
stearic  acid.           '2967     ,,      tristearin. 
cerotic  acid.          '6760     „      myricin. 
resin  acids  (ordinary  colophony,  chiefly  sylvic  acid). 

General    Characteristics    of   the    Foregoing1    Indicators. 

It  is  interesting  to  notice  the  different  degrees  of  sensitiveness 
shown  by  indicators  used  in  testing  acids  and  alkalies.  This  is  well 
illustrated  by  Thompson's  experiments,  where  he  used  solutions 
of  the  indicator  containing  a  known  weight  of  the  solid  material, 
and  so  adjusted  as  to  give,  as  near  as  could  be  judged,  the  same 
intensity  of  colour  in  the  reaction. 

It  was  found  that  lacmoid,  rosolic  acid,  phenacetolin,  and 
phenolphthalein  were  capable  of  showing  the  change  of  colour 
with  one-fifth  of  the  quantity  of  acid  or  alkali  which  was  required 
in  the  case  of  methyl  orange  or  litmus ;  that  is  to  say,  in  100  c.c. 
of  liquid,  where  the  latter  took  0*5  c.c.,  the  same  effect  with  the 
former  was  gained  by  O'l  c.c. 

Another  important  distinction  is  shown  in  their  respective 
behaviour  with  mineral  and  organic  acids. 

It  is  true  the  whole  of  them  are  alike  serviceable  for  the 
mineral  acids  and  fixed  alkalies ;  but  they  differ  considerably  in 
the  case  of  the  organic  acids  and  ammonia.  Methyl  orange 
and  lacmoid  appear  to  be  most  sensitive  to  alkalies,  while 
phenolphthalein  is  most  sensitive  to  acids;  the  others  appear  to 


38  VOLUMETKIC  ANALYSIS.  §    13. 

occupy  a  position  between  these  extremes,  each  showing,  however, 
special  peculiarities.  The  distinction,  however,  is  so  marked,  that, 
as  Thompson  says,  it  is  possible  to  have  a  liquid  which  may  be 
acid  to  phenolphthalein  and  alkaline  to  lacmoid. 

The  presence  of  certain  neutral  salts  has,  too,  a  definite  effect 
on  the  sensitiveness  of  certain  indicators.  Sulphates,  nitrates, 
chlorides,  etc.,  retard  the  action  of  methyl  orange  slightly,  while  in 
the  case  of  phenacetolin  and  phenolphthalein  they  have  no  effect. 
On  the  other  hand,  neutral  salts  of  ammonia  have  such  a  disturbing 
influence  on  the  latter  as  to  render  it  useless,  unless  with  special 
precautions. 

Nitrous  acid  alters  the  composition  of  methyl  orange ;  so  also 
do  nitrites  when  existing  in  any  quantity.  Forbes  Carpenter 
has  noted  this  effect  in  testing  the  exit  gases  of  vitriol  chambers 
(/.  S.  C.  I.  v.  287). 

Sulphites  of  the  fixed  alkalies  and  alkaline  earths  are  practically 
neutral  to  phenolphthalein,  but  alkaline  to  litmus,  methyl  orange, 
and  phenacetolin. 

Sulphides,  again,  can  be  accurately  titrated  with  methyl  orange 
in  the  cold,  and  on  boiling  off  the  H2S  a  tolerably  accurate  result  can 
be  obtained  with  litmus  and  phenacetolin,  but  with  phenolphthalein 
the  neutral  point  occurs  when  half  the  alkali  is  saturated.  The 
phosphates  of  the  alkalies,  arseniates,  and  arsenites,  also  vary  in 
their  effects  on  the  various  indicators. 

Again,  boric  acid  and  the  borates  can  be  very  accurately  titrated 
by  help  of  methyl  orange  or  lacmoid  paper,  but  the  other  indicators 
are  practically  useless. 

Thompson  classifies  the  usual  neutrality  indicators  into  three 
groups.  The  methyl  orange  group,  comprising  that  substance, 
together  with  lacmoid,  dimethylamidobenzene,  cochineal  and  Congo 
red;  the  phenolphthalein  group,  consisting  of  itself  and  turmeric;  the 
litmus  group,  including  litmus,  rosolic  acid,  and  phenacetolin.  The 
methyl  orange  group  are  most  susceptible  to  alkalies,  the  phen- 
olphthalein to  acids,  and  the  litmus  somewhat  between  the  two. 
This  classification  has  nothing  to  do  with  delicacy  of  reaction,  but 
with  the  special  behaviour  of  the  indicator  under  the  same  circum- 
stances ;  for  instance,  saliva,  which  is  generally  neutral  to  litmus 
paper,  is  always  strongly  alkaline  to  lacmoid  or  Congo  red,  and  acid 
to  turmeric  paper.  Fresh  milk  reacts  very  much  in  the  same  way. 
]STo  absolutely  hard  and  fast  line  can  however  be  drawn. 

Thompson  gives  the  following  table  as  an  epitome  of  the  results 
obtained  with  indicators,  and  on  which  several  processes  have  been 
based.  The  figures  refer  to  the  number  of  atoms  of  hydrogen 
displaced  by  the  monatomic  metals,  sodium  or  potassium,  in  the 
form  of  hydrates.  Where  a  blank  is  left  it  is  meant  that  the  end- 
reaction  is  obscure.  The  figures  apply  also  to  ammonia,  except 
where  phenolphthalein  is  concerned,  and  when  boiling  solutions  are 
used.  Calcic  and  baric  hydrates  also  give  similar  results,  except 


INDICATORS. 


39 


where  insoluble  compounds  are  produced.  Lacmoid  paper  acts  in 
every  respect  like  methyl  orange,  except  that  it  is  not  affected  by 
nitrous  acid  or  its  compounds.  Turmeric  paper  behaves  exactly 
like  phenolphthalein  with  the  mineral  acids  and  also  with  thio- 
sulphuric  and  organic  acids. 


Acids. 

Methyl  Orange. 

Phenolphthalein. 

Litmus. 

Name. 

Formula. 

Cold. 

Cold. 

Boiling, 

Cold. 

Boiling. 

Sulphuric   .     .     H2SO4 

2 

2 

2 

2 

2 

Hydrochloric  . 

HC1 

I                  11 

1 

1 

Nitric     .     .     . 

HNO3 

1 

1 

1 

1 

1 

Thiosulphuric  . 

H2S2O3 

2 

2 

2 

2 

2 

Carbonic     .     . 

H2C03 

0 

1  dilute 

0 

— 

0 

Sulphurous 

H2S03 

1 

2 

— 

— 

— 

Hydrosulphurio 
Phosphoric 

H2S 
H3P04 

0 
1 

1  dilute 
2 

0 



0 

Arsenic  . 

H3AsO4 

1 

2 

— 

— 

— 

Arsenious 

H3AsO3 

0 

— 

— 

0 

0 

Nitrous  . 

HNO2 

indicator  destroyed 

1 

— 

1 

— 

Silicic     .         .     H4SiO4 

0 

— 

— 

0 

0 

Boric  .     . 

H3B03 

0 

— 

.  . 

— 

— 

Chromic 

H2CrO4 

1 

2 

2 

— 

— 

Oxalic     . 

H2C204 

— 

2 

2 

2 

2 

Acetic     . 

HC2H3O2 

— 

1 

—  . 

1  nearly 

— 

Butyric  .         .     HC4H7O2 

— 

1 

— 

1  nearly 

— 

Succinic 

H2C4H4O4 

2 

— 

2  nearly 

— 

Lactic     .         .     HC3H50:J 

— 

1 

— 

1 

— 

Tartaric  . 

H2C4H4Of 

— 

2 

— 

2 

— 

Citric     . 

H3C6H5O7 

1           — 

3 

— 

— 

— 

Allen  (Pharm.  Jour.,  May  llth,  1889)  clearly  points  out  that 
the  acid  which  enters  into  the  composition  of  an  indicator  must  be 
weaker  than  the  acid  which  it  is  required  to  estimate  by  its  means. 
The  acid  of  which  methyl  orange  is  a  salt  is  a  tolerably  strong  one, 
since  it  is  only  completely  displaced  by  the  mineral  acids;  the 
organic  acids  are  not  strong  enough  to  overpower  it  completely, 
hence  the  uncertainty  of  the  end-reaction.  The  still  weaker  acids, 
such  as  carbonic,  hydrocyanic,  boric,  oleic,  etc.,  do  not  decompose 
the  indicator  at  all,  hence  their  salts  may  be  titrated  by  it,  just  as 
if  the  bases  only  were  present.  On  the  other  hand  the  acid  of 
phenolphthalein  is  extremely  weak,  hence  its  salts  are  easily 
decomposed  by  the  organic  and  carbonic  acids.  A  combination  of 
the  two  indicators  is  frequently  of  service ;  say,  for  instance,  in  a 
mixture  of  normal  and  acid  sodic  carbonate,  if  first  titrated  with 
'phenolphthalein  and  standard  mineral  acid,  the  rose  colour  dis- 
appears exactly  at  the  point  when  the  normal  carbonate  is  saturated, 
the  bicarbonate  can  then  be  found  by  continuing  the  operation 
with  methyl  orange.  The  study  of  these  new  indicators  is  still 
imperfect,  and  requires  further  elucidation ;  meantime  there  can  be 


40  VOLUMETEIC  ANALYSIS.  §    14. 

no  question  that  the  use  of   such  as  have  been  described  is  an 
immense  advance  upon  the  old-fashioned  litmus. 


PREPARATION     OF     THE     NORMAL    ACID    AND    ALKALINE 
SOLUTIONS. 

§  14.  IT  is  quite  possible  to  carry  out  the  titration  of  acids 
and  alkalies  with  only  one  standard  liquid  of  each  kind ;  but  it 
frequently  happens  that  standard  acids  or  alkalies  are  required 
in  other  processes  of  titration  beside  mere  saturation,  and  it  is 
therefore  advisable  to  have  a  variety. 

Above  all  things  it  is  absolutely  necessary  to  have,  at  least,  one 
standard  acid  and  alkali  prepared  with  the  most  scrupulous  accuracy, 
to  use  as  foundations  for  all  others. 

I  prefer  sulphuric  acid  for  the  normal  acid  solution,  inasmuch  as 
there  is  no  difficulty  in  getting  the  purest  acid  in  commerce.  The 
normal  acid  made  with  it  is  totally  unaffected  by  boiling,  even 
when  of  full  strength,  which  cannot  be  said  of  either  nitric  or 
hydrochloric  acid.  Hydrochloric  acid  is  however  generally  pre- 
ferred by  alkali  makers,  owing  to  its  giving  soluble  compounds 
with  lime  and  similar  bases.  Nitric  and  oxalic  acids  are  also 
sometimes  convenient. 

Sodic  carbonate,  on  the  other  hand,  is  to  be  preferred  for  the 
standard  alkali,  because  it  can  readily  be  obtained  in  a  perfectly 
pure  state,  or  can  be  easily  made  by  heating  pure  bicarbonate  to  a 
temperature  of  150°  or  200°  C.  for  some  hours  in  an  air  bath,  or 
gently  igniting  over  the  gas  for  ten  or  fifteen  minutes. 

The  chief  difficulty  hitherto  with  sodic  carbonate  has  been,  that 
with  litmus  as  indicator,  the  titration  must  be  carried  on  at  a 
boiling  heat  in  order  to  get  rid  of  carbonic  acid,  which  hinders  the 
pure  blue  colour  of  the  indicator,  notwithstanding  the  alkali  may 
be  in  great  excess.  This  difficulty  is  now  set  aside  by  the  use  of 
methyl  orange.  In  case  the  operator  has  not  this  indicator 
at  hand,  litmus  gives  perfectly  accurate  results,  if  the  saturation 
is  conducted  by  rapidly  boiling  the  liquid  in  a  thin  flask  for  a 
minute  after  each  addition  of  acid  until  the  point  is  reached 
when  one  drop  of  acid  in  excess  gives  a  pink-red  colour,  which  is 
not  altered  by  further  boiling. 

As  has  been  previously  said,  these  two  standards  must  be  pre- 
pared with  the  utmost  care,  since  upon  their  correct  preparation 
and  preservation  depends  the  verification  of  other  standard 
solutions. 

It  may,  however,  be  remarked,  that  in  place  of  a  standard  solution 
of  sodic  carbonate,  which  is  of  limited  use  for  general  purposes, 
the  pure  anhydrous  salt  may  be  used  for  the  rigid  adjustment  of 
normal  acid.  In  this  case  about  2  or  3  grams  of  pure  ISVCO3 
are  freshly  heated  to  dull  redness  for  a  few  minutes  in  a  weighed 


§    14.  NORMAL    SOLUTIONS.  41 

platinum  crucible,  cooled  under  an  exsiccator,  the  exact  weight 
taken,  then  transferred  to  a  flask  by  means  of  a  funnel,  through 
which  it  is  washed  and  dissolved  with  distilled  water,  methyl 
orange  added,  and  the  operation  completed  by  running  the  acid 
of  unknown  strength  from  a  burette  divided  into  ~  c.c.  into  the 
soda  solution  in  small  quantities  until  exact  saturation  occurs. 

A  second  portion  of  sodic  carbonate  should  now  be  weighed  as 
before,  but  not  of  necessity  exactly  the  same  quantity.  Its  exact 
weight  must  be  noted ;  the  saturation  is  carried  out  precisely  as  at 
first.  The  data  for  ascertaining  the  exact  strength  of  the  acid  solu- 
tion by  calculation  are  now  in  hand. 

A  strictly  normal  acid  should  at  16°  C.  exactly  saturate  sodic 
carbonate  in  the  proportion  of  100  c.c.  to  5*3  gm. 

Suppose  that  2*46  gm.  sodic  carbonate  required  41 '5  c.c.  of  the 
acid  in  the  first  experiment,  then 

2-46  :  5-3  :  :  41'5  :  x  =  89'4  c.c. 

Again:  2'153  gm.  sodic  carbonate  required  36*32  c.c.  of  acid, 
then 

2-153  :  5-3  :  :  36'32  :  x  =  89'4  c.c. 

The  acid  may  now  be  adjusted  by  measuring  890  c.c.  into  the 
graduated  liter  cylinder,  adding  4  c.c.  from  the  burette,  or  with  a 
small  pipette,  and  filling  to  the  liter  mark  with  distilled  water. 

Finally,  the  strength  of  the  acid  so  prepared  must  be  proved  by 
taking  a  fresh  quantity  of  sodic  carbonate,  or  by  titration  with  a 
normal  sodic  carbonate  solution  previously  made  by  direct  weighing 
of  53  gm.  to  the  liter,  and  using  not  less  than  50  c.c.  for  the' 
titration,  so  as  to  avoid  as  much  as  possible  the  personal  errors  of 
measurement  in  small  quantities.  If  the  measuring  instruments 
all  agree,  and  the  operations  are  all  conducted  with  due  care,  a 
drop  or  two  in  excess  of  either  acid  or  alkali  in  50  c.c.  should 
suffice  to  reverse  the  colour  of  the  indicator. 


1.     Normal    Sodic    Carbonate. 

53  gm.  :NTa2C03  per  liter. 

This  solution  is  made  by  dissolving  53  gm.  of  pure  sodic 
monocarbonate,  previously  gently  ignited  and  cooled,  in  distilled 
water,  and  diluting  to  1  liter  at  16°  C.  If  the  pure  salt  is  not  at 
hand,  the  solution  may  be  made  as  follows : — 

About  85  gm.  of  pure  sodic  bicarbonate,  free  from  thiosulphate, 
are  heated  to  dull  redness  (not  to  fusion)  in  a  platinum  crucible, 
for  fully  ten  minutes,  to  expel  one-half  of  the  carbonic  acid,  then 
placed  under  an  exsiccator  to  cool ;  when  placed  upon  the  balance 
it  will  be  found  that  very  little  more  than  53  gm.  remains.  The 
excess  is  removed  as  quickly  as  possible,  and  the  contents  of  the 
crucible  washed  into  a  beaker,  and  as  soon  as  the  salt  is  dissolved 


42  VOLUMETKIC  ANALYSIS.  §    14?. 

the  solution  is  decanted  into  a  liter  flask  and  filled  up  to  the  mark 
with  distilled  water  at  16°  C. 


2.     Normal    Potassic    Carbonate. 
69  gin.  K2C03  per  liter. 

This  solution  is  sometimes,  though  rarely,  preferable  to  the  soda 
salt,  and  is  of  service  for  the  estimation  of  combined  acids  in  certain 
cases,  where,  by  boiling  the  compound  with  this  agent,  an  inter- 
change of  acid  and  base  occurs. 

It  cannot  be  prepared  by  direct  weighing  of  the  potassic  carbonate, 
and  is  therefore  best  established  by  titrating  a  solution  of  unknown 
strength  with  strictly  normal  acid. 

3.    Normal    Sulphuric    Acid. 
49  gm.  H2SO*  per  liter. 

About  30  c.c.  of  pure  sulphuric  acid  of  sp.  gr.  1*840,  or  there- 
abouts, are  mixed  with  three  or  four  times  the  volume  of  distilled 
water  and  allowed  to  cool,  then  put  into  the  graduated  cylinder  and 
diluted  up  to  the  liter.  The  solution  may  now  be  roughly  tested 
by  normal  alkali,  which  is  best  done  by  putting  20  c.c.  into  a 
small  beaker  or  flask  with  methyl  orange,  and  allowing  the  acid  to 
flow  from  a  burette,  divided  into  -^  c.c.,  until  the  point  of 
neutrality  is  reached.  If  more  than  20  c.c.  are  required,  the  acid  is 
too  weak ;  if  less,  too  strong.  If  the  acid  from  which  the  solution 
was  made  was  of  the  sp.  gr.  mentioned,  it  will  generally  be 
too  strong,  which  is  preferable.  The  final  adjustment  with  sodic 
carbonate  may  now  be  made  as  before  described. 

The  solution  may  also  be  controlled  by  precipitation  with  baric 
chloride,  in  which  case  10  c.c.  should  produce  as  much  baric 
sulphate  as  is  equal  to  0'49  gm.  of  sulphuric  acid,  or  49  gm.  per 
liter". 

4.    Normal    Oxalic    Acid. 
63  gm.  C204H2,2H20,  or  45  gm.  C204H2  per  liter. 

This  solution  cannot  very  well  be  established  by  direct  weighing, 
owing  to  uncertain  hydration ;  hence  it  must  be  titrated  by  normal 
alkali  of  known  accuracy. 

The  solution  is  apt  to  deposit  some  of  the  acid  at  low  tempera- 
tures, but  keeps  well  if  preserved  from  direct  sunlight,  and  will 
bear  heating  without  volatilizing  the  acid.  Very  dilute  solutions 
of  oxalic  acid  are  very  unstable;  therefore,  if  a  decinornial  or 
centinormal  solution  is  at  any  time  required,  it  should  be  made 
when  wanted.  Some  operators  prefer  potassic  tetra-oxalate  to 
oxalic  acid,  because  the  actual  strength  of  the  normal  solution  may 
at  any  time  be  verified  by  evaporating  a  measured  volume  to 


§    14.  NORMAL    SOLUTIONS.  43 

dryness,  igniting  and  weighing  the  resulting  potassic  carbonate ; 
as  this  salt  is,  however,  extremely  hygroscopic,  an  error  may  easily 
occur. 

5.    Normal    Hydrochloric    Acid. 
36-37  gm.  HC1  per  liter. 

It  has  been  shown  by  Roscoe  and  Dittmar  (/.  C.  S.  xii.  128, 
1860)  that  a  solution  of  hydrochloric  acid  containing  20  "2  per  cent, 
of  the  gas  when  boiled  at  about  760  m.m.  pressure,  loses  acid  and 
water  in  the  same  proportion,  and  the  residue  will  therefore  have 
the  constant  composition  of  20 '2  per  cent.,  or  a  specific  gravity  of 
I'lO.  About  181  gm.  of  acid  of  this  gravity,  diluted  to  one  liter, 
serves  very  well  to  form  an  approximate  normal  acid. 

The  actual  strength  may  be  determined  by  precipitation  with 
silver  nitrate,  or  by  titration  with  an  exactly  weighed  quantity  of 
pure  sodic  monocarbonate.  Hydrochloric  acid  is  useful  on  account 
of  its  forming  soluble  compounds  with  the  alkaline  earths,  but  it  has 
the  disadvantage  of  volatilizing  at  a  boiling  heat.  Dittmar  says 
that  this  may  be  prevented  by  adding  a  few  grams  of  sodic  sulphate. 
In  many  cases  this  would  be  inadmissible,  for  the  same  reason  that 
sulphuric  acid  cannot  be  used.  The  hydrochloric  acid  from  which 
standard  solutions  are  made  must  be  free  from  chlorine  gas  or 
metallic  chlorides,  and  should  leave  no  residue  when  evaporated  in 
a  platinum  vessel. 

6.     Normal    Nitric    Acid. 
63  gm.  HNO3  per  liter. 

A  rigidly  exact  normal  acid  should  be  established  by  sodic 
carbonate,  as  in  the  case  of  normal  sulphuric  and  hydrochloric  acids. 

The  nitric  acid  used  should  be  colourless,  free  from  chlorine  and 
nitrous  acid,  sp.  gr.  from  1'35  to  1*4.  If  coloured  from  the 
presence  of  nitrous  or  hyponitrous  acids,  it  should  be  mixed  with 
two  volumes  of  water,  and  boiled  until  white.  When  cold  it  may 
be  diluted  and  titrated  as  previously  described. 

\ 

7.    Normal  Caustic  Soda  or  Potash. 

40  gm.  tfaHO  or  56  gm.  KHO  per  liter. 

Pure  caustic  soda  made  from  metallic  sodium  may  now  be  readily 
obtained  in  commerce,  and  hence  it  is  easy  to  prepare  a  standard 
solution  of  exceeding  purity,  by  simply  dissolving  the  substance  in 
distilled  water  till  of  about  T05  sp.  gr.,  or  about  50  gm.  to  the 
liter,  roughly  estimating  its  strength  by  normal  acid  and  methyl 
orange ;  then  finally  adjusting  the  exact  strength  by  titrating 
50  c.c.  with  normal  acid. 

However  pure  caustic  soda  or  potash  may  otherwise  be,  they  are 
both  in  danger  of  absorbing  carbonic  acid,  and  hence  in  using 


44  VOLUMETRIC   ANALYSIS.  §    14. 

litmus  the  titratioii  must  be  conducted  with  boiling.  Methyl 
orange  permits  the  use  of  these  solutions  at  ordinary  temperature 
notwithstanding  the  presence  of  CO2. 

Soda  and  potash  may  both  be  obtained  in  commerce  sufficiently 
pure  for  all  ordinary  titration  purposes,  but  in  case  they  are  not  at 
hand  the  requisite  solutions  may  be  prepared  as  follows : — 

Two  parts  of  pure  sodic  or  potassic  carbonate  are  to  be  dissolved 
in  twenty  parts  of  distilled  water,  and  boiled  in  a  clean  iron  pot ; 
during  the  boiling,  one  part  of  fresh  quick-lime,  made  into  a  cream 
with  water,  is  to  be  added  little  by  little,  and  the  whole  boiled  until 
all  the  carbonic  acid  is  removed,  which  may  be  known  by  the  clear 
solution  producing  110  effervescence  on  the  addition  of  dilute  acid ; 
the  vessel  is  covered  closely,  and  set  aside  to  cool  and  settle ;  when 
cold,  the  clear  supernatant  liquid  should  be  poured  or  drawn  off 
and  titrated  by  normal  acid,  and  made  of  the  proper  strength 
as  directed  for  sulphuric  acid. 

Soda  solutions  may  be  freed  from  traces  of  chlorine,  sulphuric, 
silicic,  and  carbonic  acids,  by  shaking  with  Millon's  base, 
trimercur-ammomum  (C,  N.  xlii.  8). 

In  preparing  these  alkaline  solutions,  they  should  be  exposed  as 
little  as  possible  to  the  air,  and  when  the  strength  is  finally  settled, 
should  be  preserved  in  one  of  the  bottles  shown  in  fig.  19  or  20. 


8.     Semi-normal    Ammonia. 
8-5  gm.  NH3  per  liter 

For  some  years  past  I  have  used  this  strength  of  standard 
ammonia  for  saturation  analyses,  and  have  been  fully  satisfied  with 
its  behaviour ;  it  is  cleanly,  does  not  readily  absorb  carbonic  acid, 
holds  its  strength  well  for  two  or  three  months  when  kept  in  a  cool 
place  and  well  stoppered  ;  and  can  at  any  time  be  prepared  in  a  few 
minutes,  by  simply  diluting  strong  solution  of  ammonia  with  fresh 
distilled  water. 

A  normal  solution  cannot  be  used  with  safety,  owing  to  evapora- 
tion of  the  gas  at  ordinary  temperatures. 

It  is  necessary  to  add  that,  even  in  the  case  of  §•  strength, 
the  solution  should  be  titrated  from  time  to  time  against  correct 
normal  acid.  ^  ammonia  keeps  its  strength  for  a  long  time 
in  well-closed  bottles. 

9.     Standard    Caustic    Baryta    (Pettenkofer). 

Especially  serviceable  for  free  carbonic  acid  and  coloured  acid 
liquids,  such  as  commercial  vineg-ars,  etc. 

The  solution  of  caustic  baryta  is  best  made  from  the  crystallized 
hydrate.  It  is  not  advisable  to  have  the  solution  too  concentrated, 
since,  when  it  is  near  complete  saturation  it  is  apt  to  deposit  the 


§    14.  NORMAL    SOLUTIONS.  45 

hydrate  at  low  temperature.  The  corresponding  acid  may  be  either 
Y^-  oxalic,  nitric,  or  hydrochloric.  Oxalic  acid  is  recommended  by 
Pettenkofer  for  carbonic. acid  estimation,  because  it  has  no  effect 
upon  the  baric  carbonate  suspended  in  weak  solutions  ;  but  there  is 
the  serious  drawback  in  oxalic  acid,  that  in  dilute  solution  it  is 
liable  to  rapid  decomposition ;  and  as  in  my  experience  -j-j-  hydro- 
chloric acid  in  dilute  mixtures  has  no  effect  upon  the  suspended 
baric  carbonate,  it  is  preferable  to  use  this  acid. 

The  baryta  solution  is  subject  to  constant  change  by  absorption 
of  carbonic  acid,  but  this  may  be  prevented  to  a  great  extent  by 
preserving  it  in  the  bottle  shown  in  fig.  20.  A  thin  layer  of 
petroleum  oil  on  the  surface  of  the  liquid  preserves  the  baryta  at 
one  strength  for  a  long  period. 

The  reaction  between  baryta  and  yellow  turmeric  paper  is  very 
delicate,  so  that  the  merest  trace  of  baryta  in  excess  gives  a  decided 
brown  tinge  to  the  edge  of  the  spot  made  by  a  glass  rod  on  the 
turmeric  paper.  If  the  substance  to  be  titrated  is  not  too  highly 
coloured,  litmus  may  be  used  as  an  approximate  indicator  in  the 
mixture ;  this  enables  the  operator  to  find  the  exact  point  of 
saturation  more  conveniently. 

10.    Normal  Ammonio-Cupric  Solution  for  Acetic  Acid  and  free 
Acids  and  Bases  in  Earthy  and  Metallic  Solutions. 

This  acidimetric  solution  is  prepared  by  dissolving  pure  cupric 
sulphate  in  warm  water,  and  adding  to  the  clear  solution  liquid 
ammonia,  until  the  bluish-green  precipitate  which  first  appears  is 
nearly  dissolved ;  the  solution  is  then  filtered  into  the  graduated 
cylinder,  and  titrated  by  allowing  it  to  flow  from  a  pipette  graduated 
in  i  or  y'p-  c.c.  into  10  or  20  c.c.  of  normal  sulphuric  or  nitric  acid 
(not  oxalic).  While  the  acid  remains  in  excess,  the  bluish-green 
precipitate  which  occurs  as  the  drop  falls  into  the  acid  rapidly 
disappears ;  but  so  soon  as  the  exact  point  of  saturation  occurs,  the 
previously  clear  solution  is  rendered  turbid  by  the  precipitate 
remaining  insoluble  in  the  neutral  liquid. 

The  process  is  especially  serviceable  for  the  estimation  of  the  free 
acid  existing  in  certain  metallic  solutions,  i.e.  mother-liquors,  etc., 
where  the  neutral  compounds  of  such  metals  have  an  acid  reaction 
on  litmus — such  as  the  oxides  of  zinc,  copper,  and  magnesia,  and 
the  protoxides  of  iron,  manganese,  cobalt,  and  nickel;  it  is  also 
applicable  to  acetic  and  the  mineral  acids. 

If  cupric  nitrate  be  used  for  preparing  the  solution  instead  of 
sulphate,  the  presence  of  barium,  or  strontium,  or  metals  precipitable 
by  sulphuric  acid  is  of  no  consequence.  The  solution  is  stand- 
ardized by  normal  nitric  or  sulphuric  acid ;  and  as  it  slightly  alters 
by  keeping,  a  coefficient  must  be  found  from  time  to  time  by 
titrating  with  normal  acid,  by  which  to  calculate  the  results 
systematically.  Oxides  or  carbonates  of  magnesia,  zinc,  or  other 


46  VOLUMETRIC  ANALYSIS.  §    15. 

admissible  metals,  are  dissolved  in  excess  of   normal  nitric  acid, 
and  titrated  residually  with  the  copper  solution. 

Example :  1  gm.  pure  zinc  oxide  was  dissolved  in  27  c.c.  normal  acid, 
and  2"3  c.c.  normal  copper  solution  required  to  produce  the  precipitate 
=  24*7  c.c.  acid;  this  multiplied  by  0'0405,  the  coefficient  for  zinc  oxide, 
=  1-000  gm. 


ESTIMATION  OF  THE  CORRECT  STRENGTH  OF  STANDARD 
SOLUTIONS  NOT   STRICTLY  NORMAL   OR  SYSTEMATIC. 

§  15.  IN  discussing  the  preparation  of  the  foregoing  standard 
solutions,  it  has  been  assumed  that  they  shall  be  strictly  and 
absolutely  correct;  that  is  to  say,  if  the  same  measure  be  rilled 
lirst  with  any  alkaline  solution,  then  with  an  acid  solution,  and  the 
two  mixed  together,  a  perfectly  neutral  solution  shall  result,  so  that 
a  drop  or  two  either  way  will  upset  the  equilibrium. 

Where  it  is  possible  to  weigh  directly  a  pure  dry  substance,  this 
approximation  may  be  very  closely  reached.  Sodic  monocarbonate, 
for  instance,  admits  of  being  thus  accurately  weighed.  On  the 
other  hand,  the  caustic  alkalies  cannot  be  so  weighed,  nor  can 
the  liquid  acids.  An  approximate  quantity,  therefore,  of  these 
substances  must  be  taken,  and  the  exact  power  of  the  solution 
found  by  experiment. 

In  titrating  such  solutions  it  is  exceedingly  difficult  to  make  them 
so  exact  in  strength,  that  the  precise  quantity,  to  a  drop  or  two, 
shall  neutralize  each  other.  In  technical  matters  a  near  approxima- 
tion may  be  sufficient,  but  in  scientific  investigations  it  is  of  the 
greatest  importance  that  the  utmost  accuracy  should  be  obtained ; 
it  is  therefore  advisable  to  ascertain  the  actual  difference,  and  to 
mark  it  upon  the  vessels  in  which  the  solutions  are  kept,  so  that  a 
slight  calculation  will  give  the  exact  result. 

Suppose,  for  instance,  that  a  standard  sulphuric  acid  is  prepared, 
which  does  not  rigidly  agree  with  the  normal  sodic  carbonate  (not 
at  all  an  uncommon  occurrence,  as  it  is  exceedingly  difficult  to  hit 
the  precise  point) ;  in  order  to  find  out  the  exact  difference  it  must 
be  carefully  titrated  as  in  §  14.  Suppose  the  weight  of  sodic 
carbonate  to  be  1'9  gm.,  it  is  then  dissolved  and  titrated  with  the 
standard  acid,  of  which  36*1  c.c.  are  required  to  reach  the  exact 
neutral  point. 

If  the  acid  were  rigidly  exact  it  should  require  35 '85  c.c.  ;  in 
order,  therefore,  to  find  the  factor  necessary  to  bring  the  quantity  of 
acid  used  in  the  analysis  to  an  equivalent  quantity  of  normal 
strength,  the  number  of  c.c.  actually  used  must  be  taken  as  the 
denominator,  and  the  number  which  should  have  been  used,  had 
the  acid  been  strictly  normal,  as  the  numerator,  thus — 

35-85 
-— 0-993; 


©FTHE 
COLLEGE  OF 


§    15.  NOKMAL    SOLUTIONS. 


0'993  is  therefore  the  factor  by  which  it  is  necessary  to  multiply 
the  number  of  c.c.  of  that  particular  acid  used  in  any  analysis 
in  order  to  reduce  it  to  normal  strength,  and  should  be  marked 
upon  the  bottle  in  which  it  is  kept. 

On  the  other  hand,  suppose  that  the  acid  is  too  strong,  and  that 
35  "2  c.c.  were  required  instead  of  35*85, 

35-85 
353—10184; 

1-0184  is  therefore  the  factor  by  which  it  is  necessary  to  multiply 
the  number  of  c.c.  of  that  particular  acid  in  order  to  bring  it  to 
the  normal  strength.  This  plan  is  much  better  than  dodging  about 
with  additions  of  water  or  acid. 

Under  all  circumstances,  it  is  safer  to  prove  the  strength  of  any 
standard  solution  by  experiment,  even  though  its  constituent  has 
been  accurately  weighed  in  the  dry  and  pure  state. 

Further,  let  us  suppose  that  a  solution  of  caustic  soda  is  to  be 
made  by  means  of  lime  as  described  previously.  After  pouring  off 
the  clear  liquid,  water  is  added  to  the  sediment  to  extract  more 
alkaline  solution  ;  by  this  means  we  may  obtain  two  solutions,  one 
of  which  is  stronger  than  necessary,  and  the  other  weaker.  Instead 
of  mixing  them  in  various  proportions  and  repeatedly  trying  the 
strength,  we  may  find,  by  two  experiments  and  a  calculation, 
the  proportions  of  each  necessary  to  give  a  normal  solution, 
thus  :  — 

The  exact  actual  strength  of  each  solution  is  first  found,  by 
separately  running  into  10  c.c.  of  normal  acid  as  much  of  each 
alkaline  solution  as  will  exactly  neutralize  it.  We  have,  then,  in 
the  case  of  the  stronger  solution,  a  number  of  c.c.  required  less 
than  10.  Let  us  call  this  number  V. 

In  the  weaker  solution  the  number  of  c.c.  is  greater  than  10, 
represented  by  v.  A  volume  of  the  stronger  solution  =  x  will 
saturate  10  c.c.  of  normal  acid  as  often  as  V  is  contained  in  x. 

A  volume  of  the  weaker  solution  =  y  will,  in  like  manner,  saturate 

—  ^—  c.c.  of   normal  acid  ;   both  together  saturate     y     +  -  — 

and  the  volume  of  the  saturated  acid  is  precisely  that  of  the  two 
liquids,  thus-  1()  x  1Q 

_    +       _-*      =     X      +      ym 

Whence  IQ  v  x  +  10  V  y  =  V  v  x  +  V  v  y 

v  x  (10  -  V)  =  V  y(v  -  10). 

And  lastly,  ^T  .         _  AX 

as       V  (v  -  10) 

~j  =  v  (10  -  V) 

An  example  will  render  this  clear.  A  solution  of  caustic  soda 
was  taken,  of  which  5  -8  c.c.  were  required  to  saturate  10  c.c.  normal 


48  VOLUMETRIC  ANALYSIS.  §    15. 

acid  ;  of  another  solution,  12  '7  c.c.  were  required.     The  volumes  of 
each  necessary  to  form  a  normal  solution  were  found  as  follows  :  — 

5-8  (12-7  -10)=  15-66 
12-7(10    -5-8)  -53-34 

Therefore,  if  the  solutions  are  mixed  in  the  proportion  of  15  -6  6 
c.c.  of  the  stronger  with  53'34  c.c.  of  the  weaker,  a  correct  solution 
ought  to  result.  The  same  principle  of  adjustment  is,  of  course, 
applicable  to  standard  solutions  of  every  class. 

Again  :  suppose  that  a  standard  solution  of  sulphuric  acid  has 
been  made,  approximating  as  nearly  as  possible  to  the  normal 
strength,  and  its  exact  value  found  by  f  precipitation  with  baric 
chloride,  or  a  standard  hydrochloric  acid  with  silver  nitrate,  and 
such  a  solution  has  been  calculated  to  require  the  coefficient  0'995 
to  convert  it  to  normal  strength,  —  by  the  help  of  this  solution, 
though  not  strictly  normal,  we  may  titrate  an  approximately  normal 
alkaline  solution  thus  :  —  Two  trials  of  the  acid  and  alkaline  solu- 
tions show  that  50  c.c.  alkali  =48'5  c.c.  acid,  having  a  coefficient 
of  0*995  =  48*25  c.c.  normal  ;  then,  according  to  the  equation, 
x  50  =  48*25  is  the  required  coefficient  for  the  alkali. 


= 

And  here,  in  the  case  of  the  alkaline  solution  being  sodic  carbonate, 
we  can  bring  it  to  exact  normal  strength  by  a  calculation  based  on 
the  equivalent  weight  of  the  salt,  thus  — 

1   :  0-965  :  :  53  :  5M45. 

The  difference  between  the  two  latter  numbers  is  1'855  gm.,  and 
this  weight  of  pure  sodic  carbonate,  added  to  one  liter  of  the 
solution,  will  bring  it  to  normal  strength. 


§  15. 


SYSTEMATIC   TABLE. 


TABLE    FOB   THE    SYSTEMATIC    ANALYSIS   OF   ALKALIES, 
ALKALINE    EARTHS    AND    ACIDS. 


Substance. 

Formula. 

Atomic 
Weight. 

Quantity  to  be 
weighed  so  that  1 
c.c.  Normal  Solu- 
tion^ per  cent. 
of  substance. 

Normal 
Factor.* 

Soda 

Na2O 

62 

3'1  gm. 

0'031 

Sodic  Hydrate      .     . 

NaHO 

40 

4'0  gm. 

0*040 

Sodic  Carbonate    .     . 

Na2CO3 

106 

5'3  gm. 

0-053 

Sodic  Bicarbonate 

NaHCO3 

84 

8'4  gm. 

0-084 

Potash    

K20 

94 

4'7  gm. 

0-047 

Potassic  Hydrate  .     . 

KHO 

56 

5'6  gm. 

0-056 

Potassic  Carbonate    . 

K2C03 

138 

6'9  gm. 

0-069 

Potassic  Bicarbonate 

KHCO3 

100 

lO'O  gm. 

O'lOO 

Ammonia    .... 

NH3 

17 

1*7  gm. 

0-017 

Animonic  Carbonate 

(NH4)2C03 

96 

4*8  gm. 

0-048 

Lime  (Calcic  Oxide)  . 

CaO 

56 

2'8  gm. 

0-028 

Calcic  Hydrate     .     . 

CaH2O2 

74 

3'7  gm. 

0-037 

Calcic  Carbonate  .     . 

CaCO3 

100 

5"0  gm. 

O'OSO 

Baric  Hydrate      .     . 

BaH202 

171 

8'55  gm. 

0-0855 

Do.    (Crystals) 

BaO2H2(H20)8 

315 

15-75  gm. 

0-1575 

Baric  Carbonate   .     . 

BaCO3 

197 

9'85  gm. 

0-0985 

Strontia 

SrO 

103'5 

5-175  gm. 

0*05175 

Strontic  Carbonate   . 

SrCO3 

147-5 

7-375  gm. 

0-07375 

Magnesia     .... 

MgO 

40 

2-00  gm. 

0-020 

Magnesic  Carbonate  . 

MgCO3 

84 

4'20  gm. 

0-042 

Nitric  Acid      .     .     . 

HNO3 

63 

6'3  gm. 

0-063 

Hydrochloric  Acid   . 

HC1 

36-37 

3'637  gm. 

0-03637 

Sulphuric  Acid     .     . 

H2SO4 

98 

4'9  gm. 

0-049 

Oxalic  Acid      .     .     . 

C204H2(H20)2 

126 

6-3  gm. 

0-063 

Acetic  Acid     .     .     . 

C202H4 

60 

6'0  gm. 

0*060 

Tartaric  Acid  .     .     . 

C406H6 

150 

7*5  gm. 

0-075 

Citric  Acid  .... 

C°0'H8+H20 

210 

7'0  gm. 

0-070 

Carbonic  Acid  .     .     . 

CO2 

44 

0-022 

*  This  is  the  coefficient  by  which  the  number  of  c.c.  of  normal  solution  used  in 
any  analysis  is  to  be  multiplied,  in  order  to  obtain  the  amount  of  pure  substance 
present  in  the  material  examined. 

If  grain  weights  are  used  instead  of  grams,  the  decimal  point  must  be  moved 
one  place  to  the  risrht  to  give  the  necessary  weight  for  examination ;  thus  sodic 
carbonate,  instead  of  5 '3  gm.,  would  be  53  grains ;  the  normal  factor  in  this  case  would 
also  be  altered  to  0'53. 


50  VOLUMETEIC  ANALYSIS.  §    16. 

THE    TITRATION    OF    ALKALINE    SALTS. 
1.    Caustic  Soda  or  Potash,  and  their  Neutral  or  Acid  Carbonates. 

§  16.  THE  necessary  quantity  of  substance  being  weighed  or 
measured,  as  the  case  may  be,  and  mixed  with  distilled  water  to  a 
proper  state  of  dilution  (say  about  one  per  cent,  of  solid  material), 
an  appropriate  indicator  is  added,  and  the  solution  is  ready  for  the 
burette.  Normal  acid  is  then  cautiously  added  from  a  burette 
till  the  change  of  colour  occur.  In  the  case  of  caustic  alkalies 
free  from  CO2,  the  end-reaction  is  very  sharp  with  any  of  the 
indicators ;  but  if  CO2  is  present,  the  only  available  indicators  in 
the  cold  are  methyl  orange  or  lacmoid  paper.  If  the  other  indica- 
tors are  used,  the  CO2  must  be  boiled  off  after  each  addition  of  acid. 

In  examining  carbonates  of  potash  or  soda,  or  mixtures  of  caustic 
and  carbonate,  where  it  is  only  necessary  to  ascertain  the  total 
alkalinity,  the  same  method  applies. 

In  the  examinations  of  samples  of  commercial  refined  soda  or 
potash  salts,  it  is  advisable  to  proceed  as  follows : — 

Powder  and  mix  the  sample  thoroughly,  weigh  10  gm.  in  a  platinum  or 
porcelain  crucible,  and  ignite  gently  over  a  spirit  or  gas  lamp,  and  allow  the 
crucible  to  cool  under  the  exsiccator.  "Weigh  again,  the  loss  of  weight  gives 
the  moisture ;  wrash  the  contents  of  the  crucible  into  a  beaker,  dissolve  and 
filter  if  necessary,  and  dilute  to  the  exact  measure  of  500  c.c.  with  distilled 
water  in  a  half -liter  flask ;  after  mixing  it  thoroughly  take  out  50  c.c.  =  1  gm. 
of  alkali  with  a  pipette,  and  empty  it  into  a  small  flask,  bring  the  flask  under 
a  burette  containing  normal  acid  and  graduated  to  4-  or  TV  c.c.,  allow  the  acid 
to  flow  cautiously  as  before  directed,  until  the  neutral  point  is  reached :  the 
process  may  then  be  repeated  several  times  if  necessary,  in  order  to  be  certain 
of  the  correctness  of  the  analysis. 

Residual  Titration :  As  the  presence  of  carbonic  acid  with  litmus  and  the 
other  indicators,  except  methyl  orange,  always  tends  to  confuse  the  exact  end 
of  the  process,  the  difficulty  is  best  overcome,  in  the  case  of  not  using  methyl 
orange,  by  allowing  an  excess  of  acid  to  flow  into  the  alkali,  boiling  to  expel 
the  CO2,  and  then  cautiously  adding  normal  caustic  alkali,  drop  by  drop, 
until  the  liquid  suddenly  changes  colour;  by  deducting  the  quantity  of 
caustic  alkali  from  the  quantity  of  acid  originally  used,  the  exact  volume  of 
acid  necessary  to  saturate  the  1  gm.  of  alkali  is  ascertained. 

This  method  of  re-titration  gives  a  very  sharp  end-reaction,  as- 
there  is  no  carbonic  acid  present  to  interfere  with  the  delicacy  of 
the  indicator.  It  is  a  procedure  sometimes  necessary  in  other  cases, 
owing  to  the  interference  of  impurities  dissipated  by  boiling,  e.g. 
sulphuretted  hydrogen,  which  would  otherwise  bleach  the  indicator, 
except  in  the  case  of  methyl  orange  and  lacmoid  paper,  either  of 
which  are  indifferent  to  H2S  in  the  cold.  An  example  will  make 
the  plan  clear : — 

Example :  50  c.c.  of  the  solution  of  alkali  prepared  as  directed,  equal  to 
1  gm.  of  the  sample,  is  put  into  a  flask,  and  20  c.c.  of  normal  acid  allowed  to 
flow  into  it ;  it  is  then  boiled  and  shaken  till  all  CO2  is  expelled,  and  normal 
caustic  alkali  added  till  the  neutral  point  is  reached ;  the  quantity  required 
is  3*4  c.c.,  which  deducted  from  20  c.c.  of  acid  leaves  1G'6  c.c.  The  follow- 


8    16.  ALKALINE  SALTS.  51 

o 

ing  calculation,  therefore,  gives  the  percentage  of  real  alkali,  supposing  it 
to  be  soda : — 31  is  the  half  molecular  weight  of  dry  soda  (Na2O*)  and  1  c.c. 
of  the  acid  is  equal  to  0'031  gin.,  therefore  16'6  c.c.  is  multiplied  by  0'031, 
which  gives  0'5146 ;  and  as  1  gm.  was  taken,  the  decimal  point  is  moved 
two  places  to  the  right,  which  gives  51*46  per  cent,  of  real  alkali ;  if  calculated 
as  carbonate,  the  16'6  would  be  multiplied  by  0'053,  which  gives  0'8798  gm. 
=  87*98  per  cent. 

2.    Mixed    Caustic    and    Carbonated    Alkaline    Salts. 

The  alkaline  salts  of  commerce,  and  also  alkaline  lyes  used  in 
soap,  paper,  starch,  and  other  manufactories,  consist  often  of  a 
mixture  of  caustic  and  carbonated  alkali.  If  it  be  desired  to 
ascertain  the  proportion  in  which  these  mixtures  occur,  the  total 
alkaline  power  of  a  weighed  or  measured  quantity  of  substance  (not 
exceeding  1  or  2  gm.)  is  ascertained  by  normal  acid  and  noted;  a 
like  quantity  is  then  dissolved  in  about  150  c.c.  of  water  in  a 
200  c.c.  flask,  and  enough  solution  of  baric  chloride  added  to 
remove  all  carbonic  acid  from  the  soda  or  potash. 

Watson  Smith  has  shown  (J.  S.  C.  I.  i.  85)  that  whenever  an 
excess  of  baric  chloride  is  used  in  this  precipitation  so  as  to  form 
baric  hydrate,  there  is  an  invariable  loss  of  soda :  exact  precipita- 
tion is  the  only  way  to  secure  accuracy. 

The  flask  is  now  filled  up  to  the  200  c.c.  mark  with  distilled 
water,  securely  stoppered,  and  put  aside  to  settle.  When  the 
supernatant  liquid  is  clear,  take  out  50  c.c.  with  a  pipette,  and 
titrate  with  normal  hydrochloric  acid  to  the  neutral  point.  The 
number  of  c.c.  multiplied  by  4  will  be  the  quantity  of  acid  required 
for  the  caustic  alkali  in  the  original  weight  of  substance,  because 
only  one-fourth  was  taken  for  analysis.  The  difference  is  calculated 
as  carbonate,  or  the  precipitated  baric  carbonate  may  be  thrown 
upon  a  dry  filter,  washed  well  and  quickly  with  boiling  water,  and 
titrated  with  normal  acid,  instead  of  the  original  analysis  for  the 
total  alkalinity ;  or  both  plans  may  be  adopted  as  a  check  upon 
each  other. 

The  principle  of  this  method  is,  that  when  baric  chloride  is  added 
to  a  mixture  of  caustic  and  carbonated  alkali,  the  carbonic  acid  of 
the  latter  is  precipitated  as  an  equivalent  of  baric  carbonate,  while 
the  equivalent  proportion  of  caustic  alkali  remains  in  solution  as 
baric  hydrate.  By  multiplying  the  number  of  c.c.  of  acid  required 
to  saturate  this  free  alkali  with  the  l016o  atomic  weight  of  caustic 
potash  or  soda,  according  to  the  alkali  present,  the  quantity  of 
substance  originally  present  in  this  state  will  be  ascertained. 

As  caustic  baryta  absorbs  CO2  very  readily  when  exposed  to  the 
atmosphere,  it  is  preferable  to  allow  the  precipitate  of  baric 
carbonate  to  settle  in  the  flask  as  here  described,  rather  than  to 
filter  the  solution  as  recommended  by  some  operators,  especially 
also  as  the  filter  obstinately  retains  some  baric  hydrate. 

*  The  commercial  standard  (so  called  English  test)  often  used  is  32  (being  based  on 
the  old  erroneous  equivalent  of  Na=24). 

v    9 


52  VOLUMETRIC  ANALYSIS.  §    16. 

A  very  slight  error,  however,  occurs  in  all  such  cases,  in 
consequence  of  the  volume  of  the  precipitate  being  included  in 
the  measured  liquid. 

K.  Williams  (/.  S.  C.  I.  vi.  346)  estimates  the  caustic  soda  in 
soda  ash  by  digesting  a  weighed  quantity  in  strong  alcohol  in  a 
tightly  stoppered  flask  with  frequent  shaking  and  finally  allowing 
to  stand  overnight;  the  undissolved  carbonate  is  filtered  off, 
washed  with  alcohol  until  a  drop  gives  no  alkaline  reaction — 
the  filtrate  and  washings  are  then  titrated  with  normal  acid  and 
phenolphthalein. 

Peter  Hart  recommends  the  following  method  of  ascertaining 
the  relative  proportions  of  caustic  and  carbonated  soda  in  soda  ash : — 
50  grains  of  the  sample  is  dissolved  in  10  ounces  of  water, 
phenolphthalein  added,  and  the  standard  acid  (1  dm.  =  0*5  grn. 
Na20)  slowly  run  in  until  the  colour  disappears.  At  this  point  all 
the  caustic  soda  and  one-half  the  carbonate  has  been  neutralized, 
say  30  dm.  has  been  used.  To  the  same  solution  (in  which  the 
soda  now  exists  as  bicarbonate)  methyl  orange  is  added,  and  the 
titration  continued  until  pink :  the  burette  now  reads  50  dm. 
Then  50—30  =  20  as  NaHCO3,  but  as  this  originally  existed  in  the 
sample  as  Na2C03,  this  figure  must  be  doubled  =  40,  which 
deducted  from  50  leaves  10  dm.  as  representing  the  caustic  soda 
in  the  sample. 

3.    Estimation    of   Hydrates    of    Soda    or    Potash    with    small 
proportions    of    Carbonate. 

This  may  be  accomplished  by  means  of  phenacetolin  (Lunge, 
J.  S.  C.  I.  i.  56.)  The  alkaline  solution  is  coloured  of  a  scarcely 
perceptible  yellow  with  a  few  drops  of  the  indicator.  The 
standard  acid  is  then  run  in  until  the  yellow  gives  place  to  a  pale 
rose  tint :  at  this  point  all  the  caustic  alkali  is  saturated,  and  the 
volume  of  acid  used  is  noted.  Further  addition  of  acid  now 
intensifies  this  red  colour  until  the  carbonate  is  decomposed,  when 
a  clear  golden  yellow  results.  The  neutralization  of  the  NaHO  or 
the  KHO  is  indicated  by  a  rose  tint  permanent  on  standing ;  that 
of  ]N"a2C03  or  K2C03  by  the  sudden  passage  from  red  to  yellow. 

Practice  is  required  with  solutions  of  known  composition  to 
accustom  the  eye  to  the  changes  of  colour.  Phenolpthalein  may 
also  be  employed  for  the  same  purpose  as  follows  : — 

Add  normal  acid  to  the  cold  alkaline  solution  till  the  red  colour 
is  discharged,  taking  care  to  use  a  very  dilute  solution,  and  keeping 
the  spit  of  the  burette  in  the  liquid  so  that  no  CO2  escapes.  The 
point  at  which  the  colour  is  discharged  occurs  when  all  the  hydrate 
is  neutralized  and  the  carbonate  converted  into  bicarbonate ;  the 
volume  of  acid  is  noted,  and  the  solution  heated  to  boiling,  with 
small  additions  of  acid,  till  the  red  colour  produced  by  the  decom- 
position of  the  bicarbonate  is  finally  destroyed. 


§16.  ALKALINE   SALTS.  53 

In  both  these  methods  it  is  preferable,  after  the  first  stage,  to 
add  excess  of  acid,  boil  off  the  CO2,  and  titrate  back  with  normal 
alkali.  The  results  are  quite  as  accurate  as  the  method  of  precipi- 
tation with  barium. 


4.    Estimation    of   Alkaline    Bicarbonates    in    presence    of 
Normal    Carbonates    (Lunge,  J.  S.  C.  I.  i.  57). 

To  a  weighed  quantity  of  the  solid  bicarbonate,  or  a  measured 
quantity  of  a  solution,  there  is  added  an  excess  of  |-  ammonia, 
followed  by  an  excess  of  solution  of  baric  chloride.  The  mixture 
is  made  in  a  measuring  flask,  and  the  whole  diluted  with  hot 
distilled  water  to  the  mark. 

A  portion  of  the  clear  settled  liquid,  or  filtered  through  a  dry 
filter,  is  then  titrated  with  normal  acid :  the  alkaline  strength  due 
to  the  excess  of  ammonia,  above  that  required  to  convert  the  bicar- 
bonate into  normal  carbonate,  deducted  from  the  total  ammonia 
added,  gives  the  equivalent  of  the  bicarbonate  present. 

Example  (Lunge)  :  20  gin.  sodic  bicarbonate  in  the  course  of  manufac- 
ture were  dissolved  to  a  liter.  50  c.c.  of  this  solution  required  12'1'o.c. 
normal  acid  =  0'3751  gm.  Na2O ;  50  c.c.  were  then  mixed  with  50  c.c.  of 
standard  ammonia  (50  c.c.  =  24'3  normal  acid)  and  the  whole  treated  with 
excess  of  baric  chloride.  One  half  of  the  clear  liquid  required  6'25  c.c. 
normal  acid  =  11*8  c.c.  corrected  for  strength  and  double  quantity:  this  is, 
therefore,  the  equivalent  of  the  CO2  as  bicarbonate. 

NaHCO3  :  ll'Sx '084= '9912  gm. 
Na2CO3  :  (12'1— 11'8)  x  "053  =  '0159. 

A  simpler  plan  than  the  above  has  been  devised  by  Thompson, 
which  gives  good  results  when  carefully  carried  out. 

To  the  cold  solution  of  the  sample,  an  excess  of  normal  caustic 
soda,  free  from  CO2,  is  added,  the  CO2  is  then  precipitated  with 
neutral  solution  of  baric  chloride,  and  the  excess  of  sodic  hydrate 
found  by  standard  acid,  using  phenolphthalein  as  indicator.  The 
precipitate  of  baric  carbonate  has  no  effect  on  the  indicator  in  the 
cold.  The  calculation  is  the  same  as  before. 


5.    Estimation    of    small    quantities    of   Sodic    or    Potassic 
Hydrates    in    presence    of    Carbonates. 

This  method,  by  Thompson,  has  just  been  alluded  to,  and 
consists  in  precipitating  the  carbonates  by  neutral  solution  of  baric 
chloride  in  the  cold :  the  baric  carbonate  being  neutral  to  phenol- 
phthalein, this  indicator  can  be  used  for  the  process.  When  the 
•barium  solution  is  added,  a  double  decomposition  occurs,  resulting 
in  an  equivalent  quantity  of  sodic  or  potassic  chloride,  while  the 
baric  carbonate  is  precipitated,  and  the  alkaline  hydrate  remains  in 
solution. 


54  VOLUMETKIC  ANALYSIS.  §    16. 

Example  (Thompson):  2  gm.  of  pure  sodic  carbonate  were  mixed  in 
solution  with  '02  gm.  of  sodic  hydrate ;  excess  of  baric  chloride  was  then 
added,  together  with  the  indicator,  and  the  solution  titrated  with  -^  acid,  of 
which  in  three  trials  an  average  of  5  c.c.  was  required;  therefore, 
5  x  '004 ='02  gm.  exactly  the  quantity  used. 

In  this  process  the  presence  of  chlorides,  sulphates,  and  sulphites 
do  not  interfere ;  neither  do  phosphates,  as  baric  phosphate  is 
neutral  to  the  indicator.  With  sulphides,  half  of  the  base  will  be 
estimated;  but  if  hydrogen  peroxide  be  added,  and  the  mixture 
allowed  to  rest  for  a  time,  the  sulphides  are  oxidized  to  sulphates, 
which  have  no  effect.  If  silicates  or  aluminates  of  alkali  are 
present,  the  base  will  of  course  be  recorded  as  hydrate. 

.Thompson  further  says: — 

"  The  foregoing  method  can  also  be  applied  to  the  determination 
of  hydrate  of  sodium  or  potassium  in  various  other  compounds, 
which  give  precipitates  with  baric  chloride  neutral  to  phenolph- 
thalein,  such  as  the  normal  sulphites  and  phosphates  of  the  alkali 
metals.  An  illustration  of  the  use  to  which  the  facts  I  have 
stated  in  this  and  former  papers  may  be  put  will  be  found  in  the 
analysis  of  sulphite  of  sodium.  Of  course  sulphate,  thiosulphate, 
and  chloride  are  determined  as  usual,  but  to  estimate  sulphite, 
carbonate  and  hydrate,  or  bicarbonate  of  sodium  by  methods  in 
ordinary  use  is  rather  a  tedious  operation.  To  find  the  proportion 
of  hydrate,  all  that  is  necessary  is  to  precipitate  with  baric  chloride 
and  titrate  with  standard  acid,  as  above  described.  Then,  by 
simple  titration  of  another  portion  of  the  sample  in  the  cold,  using 
phenolphthalein  as  indicator,  the  hydrate  and  half  of  the  carbonate 
can  be  found,  and  finally,  by  employment  of  methyl  orange  as 
indicator,  and  further  addition  of  acid,  the  other  half  of  the 
carbonate  and  half  of  the  sulphite  can  be  estimated.  By  simple 
calculations,  the  respective  proportions  of  these  three  compounds 
can  be  obtained,  a  result  which  can  be  accomplished  in  a  few 
minutes.  It  must  be  borne  in  mind  that  if  a  large  quantity  of 
eodic  carbonate  is  in  the  sample  the  proportion  of  that  compound 
found  will  only  be  an  approximation  to  the  truth,  as  the 
end-reaction  is  only  delicate  "with  small  proportions  of  sodic 
carbonate.  If  there  is  no  hydrate  found,  bicarbonate  of  sodium 
can  be  tested  for,  and  determined  by  Lunge's  method  described 
above  "(§16- 4). 


6.      Estimation    of   Alkalies    in    the    presence    of   Sulphites. 

It  is  not  possible  to  estimate  the  alkaline  compounds  in  the 
presence  of  sulphites  by  titration  with  acids,  as  a  certain  quantity 
of  acid  is  taken  up  by  the  sulphite,  SO2  being  evolved.  This 
difficulty  may  be  completely  overcome  by  the  aid  of  hydrogen 
peroxide,  which  speedily  converts  the  sulphites  into  sulphates 
(Grant  and  Cohen,  /.  S.  C.  I.  ix.  19).  These  operators  proved 


§    16.  ALKALINE   SALTS.  55 

that  neither  caustic  or  carbonated  alkali  were  affected  by  H202,  nor 
had  the  latter  any  prejudicial  effect  on  methyl  orange  in  the  cold. 
The  quantity  of  H202  required  in  any  given  analysis  must  depend 
on  the  amount  of  sulphite  present;  for  instance,  the  caustic 
salts  of  commerce  contain  about  50%  of  sulphite,  and  it  suffices 
to  take  10  c.c.  of  ordinary  10  vol.  H202  for  every  O'l  gin.  of  the 
salts  in  solution.  In  the  case  of  mixtures  containing  less  or  more 
sulphite  the  quantity  may  be  varied. 

The  Analysis :  A  measured  volume  of  the  peroxide  is  run  into  a  beaker, 
and  three  or  four  drops  of  methyl  orange  added.  As  the  H2O2  is  invariably 
faintly  acid,  the  acidity  is  carefully  corrected  by  adding  drop  by  drop  from  a 
pipette  T-^jy  caustic  soda.  The  required  quantity  of  salt  to  be  analyzed  is 
then  added  in  solution,  and  the  mixture  gently  boiled,  during  the  boiling  the 
methyl  orange  will  be  bleached.  The  liquid  is  then  cooled,  a  drop  or  two 
more  of  methyl  orange  added,  and  the  titration  for  the  proportion  of  alkali 
carried  out  with  normal  acid  in  the  usual  way.  The  results  are  very 
satisfactory. 

7.      Estimation    of    Caustic    Soda    or    Potash,    by    standard 
Bichromate    of   Potash. 

This  process  was  devised  by  Richter,  or  rather  the  inverse  of 
it,  for  estimating  bichromate  with  caustic  alkali  by  the  aid  of 
phenolphthaleiii.  Exact  results  may  be  obtained  by  it  in  titrating 
soda  or  potash  as  hydrates,  but  not  ammonia  as  recommended 
by  Richter. 

For  the  process  there  are  required  a  decinormal  solution  of  bichromate  con- 
taining 14*74  gm.  per  liter,  and  T^  soda  or  potash  solution  titrated  against 
sulphuric  acid.  A  comparison  liquid  containing  about  1  gm.  of  monochro- 
niate  of  potash  in  150 — 200  c.c.  water  is  advisable  for  ascertaining  the  exact 
end  of  the  reaction ;  50  c.c.  of  the  alkali  being  diluted  with  the  same  volume 
of  water,  is  coloured  with  phenolphthalein,  and  the  bichromate  run  in  from 
a  burette ;  the  fine  red  tint  changes  to  reddish  yellow,  which  remains  till 
the  neutral  point  is  nearly  reached,  when  the  yellow  colour  of  the  mono- 
chromate  is  produced ;  the  change  is  not  instantaneous  as  with  mineral  acids, 
so  that  a  little  time  must  be  allowed  for  the  true  colour  to  declare  itself. 


8.    Estimation    of   Potash    in    Neutral    Salts    free    from    Soda. 

Stolba  precipitates  the  potash  from  a  tolerably  concentrated  solution  of 
the  substances  with  hydrofluosilicic  acid  and  strong  alcohol.  The  method  is 
also  applicable  to  the  estimation  of  potash  in  potassic  platinum  chloride.  To 
ensure  complete  decomposition,  it  is  well  to  warm  the  mixture  for  a  little 
time  before  adding  the  alcohol,  which  must  be  of  about  the  same  volume  as 
the  liquid  itself.  After  some  hours,  when  the  precipitate  has  settled,  the 
solution  is  filtered  off,  the  beaker  and  precipitate  well  washed  with  equal 
mixtures  of  alcohol  and  water,  the  whole  transferred  to  a  white  porcelain 
basin,  water  rather  freely  added,  and  heated  to  boiling,  a  few  drops  of 
litmus  added,  and  normal  or  semi-normal  alkali  run  in  until  exact 
saturation  occurs ;  or  a  known  excess  of  alkali  may  be  added,  and  the  amount 
found  by  residual  titration  with  normal  acid.  The  results  are  generally 
about  1°/0  too  low,  owing  to  the  difficulty  of  fully  decomposing  the  pre- 
cipitate. 

2  eq.  alkali  =  1  eq.  potash. 


56  VOLUMETRIC   ANALYSIS.  §    16. 

The  process  is  very  limited  in  its  use,  and  is  not  applicable  when 
sulphates  are  present,  nor  in  the  presence  of  any  great  amount  of 
free  acid.  Sulphuric  acid  may  be  previously  removed  by  calcic 
acetate  and  alcohol ;  other  acids  by  moderate  ignition  previous  to 
precipitation.  Large  proportions  of  ammonia  salts  must  also  be 
removed ;  and,  of  course,  all  other  matters  precipitable  by  hydro- 
nuosilicic  acid,  especially  soda. 

9.     Direct    estimation    of   Potash    in    the    presence    of   Soda. 

Fleischer  recommends  the  following  method;  and  my  own 
experiments  confirm  his  statements,  so  far  at  least  as  the  pure  salts 
are  concerned. 

The  solution  must  contain  no  other  bases  except  the  alkalies,  nor  any  acids 
except  nitric,  hydrochloric,  or  acetic.  This  can  almost  invariably  be  easily 
accomplished.  Earthy  alkalies  are  removed  by  ammonic  carbonate  or 
phosphate;  sulphuric,  chromic,  phosphoric,  and  arsenic  acids  by  baric 
chloride,  followed  by  ammonic  carbonate. 

The  solution  should  be  tolerably  concentrated,  and  the  volume  about  25  or 
30  c.c. ;  10 — 15  c.c.  of  neutral  solution  of  ammonic  acetate  of  sp.  gr. 
1'035  are  added ;  followed  by  finely  powdered  pure  tartaric  acid  in  sufficient 
quantity  to  convert  the  potash  into  acid  tartrate,  with  an  excess  to  form  some 
ammonic  tartrate,  but  not  enough  to  decompose  the  whole.  This  is  the  weak 
part  of  the  method ;  however,  as  a  guide,  it  is  not  advisable  to  add  more 
than  5  gni.  tartaric  acid  for  10  c.c.  of  ammonic  acetate.  If  the  quantity  of 
potash  is  approximately  known,  it  is  best  to  add  about  one-third  more  than 
is  sufficient  to  convert  the  whole  into  acid  tartrate. 

After  adding  the  tartaric  acid  the  mixture  must  be  well  stirred  for  five  or 
ten  minutes,  without  rubbing  the  sides  of  the  beaker ;  a  like  volume  of  95- 
per-cent.  alcohol  is  added,  and  again  well  stirred.  The  precipitate  contains 
the  whole  of  the  potash  as  tartrate,  and  a  portion  of  ammonium  tartrate. 
After  standing  half  an  hour  with  occasional  stirring,  the  precipitate  is 
collected  on  a  porous  filter,  and  repeatedly  washed  with  alcohol  and  water  in 
equal  parts  until  clean. 

When  the  washing  is  finished  the  precipitate  will  be  entirely  free  from 
soda ;  filter  and  precipitate  are  transferred  to  a  porcelain  basin,  treated  with 
sufficient  hot  water  to  dissolve  the  tartrates,  then  exactly  neutralized  with 
normal  alkali  and  litmus,  and  the  volume  so  used  noted.  A  like  volume,  or 
preferably,  a  larger  known  volume  of  normal  alkali  is  now  added,  and  the 
mixture  boiled  to  expel  all  ammonia;  the  end  maybe  known  by  holding 
litmus  paper  in  the  steam.  The  excess  of  normal  alkali  is  now  found  by 
titration  with  normal  acid  ;  the  amount  so  found  must  be  deducted  from  that 
which  was  added  in  excess  after  the  exact  titration  of  the  tartrate ;  the 
difference  equals  the  ammonia  volatilized.  By  deducting  this  difference 
from  the  volume  of  normal  alkali  originally  required,  the  volume  corre- 
sponding to  potash  is  found. 

Example  :  29'4  c.c.  of  normal  alkali  were  required  in  the  first  instance  to 
neutralize  a  given  precipitate ;  40  c.c.  of  the  same  alkali  were  then  added, 
the  boiling  accomplished,  and  22'5  c.c.  normal  acid  used  for  the  excess ;  then 
40— 22'5  =  17'5  c.c.,  and  again  29'4— 17'5  =  11'9,  which  multiplied  by  the 
factor  for  K^O=0'056  gives  0'6664  gm. 

The  soda  in  filtrate  may  be  obtained  by  evaporation  with  hydro- 
chloric acid  as  sodic  chloride,  and  estimated  as  in  §  38. 


§    16.  ALKALINE   SALTS.  57 

10.     Mixed    Caustic    Soda    and    Potash. 

This  process  depends  upon  the  fact,  that  potassic  bitartrate  is 
almost  insoluble  in  a  solution  of  sodic  bitartrate. 

Add  to  the  solution  containing  the  mixed  salts  a  standard  solution  of 
tartaric  acid  till  neutral  or  faintly  acid — this  produces  neutral  tartrates 
of  the  alkalies— now  add  the  same  volume  of  standard  tartaric  acid  as  before — 
they  are  now  acid  tartrates,  and  the  potassic  bitartrate  separates  almost 
completely,  filter  off  the  sodic  bitartrate  and  titrate  the  filtrate  with  normal 
caustic  soda ;  the  quantity  required  equals  the  soda  originally  in  the 
mixture — the  quantity  of  tartaric  acid  required  to  form  bitartrate  with  the 
soda  subtracted  from  the  total  quantity  added  to  the  mixture  of  the  two 
alkalies,  gives  the  quantity  required  to  form  potassic  bitartrate,  and  thus 
the  quantity  of  potash  is  found. 

This  process  is  only  applicable  for  technical  purposes. 

Mixtures  of  potash  and  soda  in  the  form  of  neutral  chlorides  are 
estimated  by  J.  T.  White  as  follows  (C.  N.  Ivii.  214) :— 20  c.c.  of  the 
solution  containing  about  0  2  gm.  of  the  mixed  salts  are  placed  into 
a  100  c.c.  flask,  and  5  c.c.  of  a  hot  saturated  solution  of  ammonic  bicarbonate 
added ;  the  mixture  is  cooled,  and  alcohol  added  in  small  quantities,  with 
shaking,  until  the  measure  is  made  up  to  100  c.c.  After  three  or  four  hours, 
10  c.c.  of  the  clear  liquid  are  removed  with  a  pipette,  evaporated  and 
ignited,  the  residue  is  moistened  with  a  few  drops  of  ammonic  chloride 
solution  and  again  ignited ;  the  sodic  chloride  so  obtained  is  then  titrated 
with  standard  silver  solution,  1  c.c.  of  which  represents  -001  gm.  Cl ;  this  is 
calculated  to  NaCl  and  the  KC1  found  by  difference. 

HUBERT  RY^gg^,  ag  platino_chloride> 


Ill  cases  where  potash  exists  in  combination  as  a  neutral  salt, 
such  as  kainit  or  kieserit,  etc.,  or  as  a  constituent  of  minerals, 
it  has  to  be  first  separated  as  double  chloride  of  potassium  and 
platinum.  The  method  usually  adopted  is  that  of  collecting  the 
double  salt  upon  a  tared  filter,  when  the  weight  of  the  dry  double 
salt  is  obtained,  the  weight  of  potash  is  ascertained  by  calculation. 

It  may,  however,  be  arrived  at  by  volumetric  means  as  follows : — 

The  potash  having  been  converted  into  double  chloride  in  the  usual  way 
is  dried,  collected,  and  mixed  with  about  double  its  weight  of  pure  sodic 
oxalate,  and  gently  smelted  in  a  platinum  crucible  ;  this  operation  results  in 
the  production  of  metallic  platinum,  chlorides  of  sodium  and  potassium, 
with  some  carbonate  of  soda.  The  quantity  of  potash  present  is,  however, 
solely  measured  by  the  chlorine ;  in  order  to  arrive  at  this,  the  fused  mass  is 
lixiviated  with  water,  filtered,  nearly  neutralized  with  acetic  acid,  and  the 
chlorine  estimated  with  &  silver  and  chromate,  the  number  of  c.c.  of  silver 
required  is  multiplied  by  the  factor  0'00157,  which  gives  at  once  the  weight 
of  potash.  This  factor  is  used  because  1  molecule  of  double  chloride  contains 
3  atoms  chlorine,  hence  the  quantity  of  ^  silver  used  is  three  times  as  much 
as  in  the  case  of  sodic  or  potassic  chloride. 


12.      Separation    of   the    Potash    as    Bitartrate. 

The  mixed  salts  being  rendered  as  nearly  neutral  as  possible,  a  saturated 
solution  of  sodic  bitartrate  is  added  in  excess,  and  the  whole  evaporated  to 
dryness  in  the  water  bath.  The  dry  mass  is  then  deprived  of  the  excess  of 


58  VOLUMETRIC  ANALYSIS.  §    16 

sodic  bitartrate  by  washing  it  on  a  filter  with  a  saturated  solution  of  potassic 
bitartrate ;  when  all  the  soda  salt  has  been  removed,  the  potash  salt  is 
dissolved  in  hot  water,  and  titrated  with  normal  alkali,  of  which  1  c.o. 
represents  0'039  gm.  K.  In  cases  where  potash  is  to  be  separated  as 
bitartrate,  the  operator  should  consult  §  25.  2  and  3. 


13.    Indirect  Estimation  of  Potash   (Dubenard). 

This  process  is  ingenious,  but,  like  all  attempts  at  estimating 
tliis  base  volumetrically,  is  not  very  exact,  except  with  extreme 
precautions. 

The  Analysis :  The  potassic  salt,  acidified  with  nitric  acid,  is  precipitated 
by  a  standard  solution  of  sodic  chloroplatinate,  the  excess  of  which  is 
reduced  by  zinc,  and  then  determined  by  means  of  standard  silver  nitrate. 
The  process  is  applicable  to  sulphates,  chlorides,  nitrates,  etc.  12  to  15  parts 
of  sodic  chloroplatinate  are  dissolved  in  100  of  alcohol,  and  12  to  15  parts  of 
silver  nitrate  in  1000  of  water.  The  solutions  are  standardized  as  follows : — 
10  c.c.  of  the  platinum  solution  are  reduced  by  boiling  for  a  minute  with  a 
small  quantit}7-  of  zinc  powder,  the  whole  of  the  platinum  being  precipitated, 
and  all  the  chlorine  remains  in  solution  as  chlorides  of  zinc  and  of  sodium ; 
the  solution  is  made  up  to  100  c.c.  and  filtered.  In  50  c.c.  of  the  filtrate  the 
chlorine  is  determined  by  titrating  with  the  silver  solution,  of  which,  say, 
40  c.c.  are  required.  Then  40  x  4  =••  160  =  the  number  of  c.c.  which 
corresponds  to  20  c.c.  of  the  platinum  solution.  0'5  gm.  of  potassic  nitrate 
or  sulphate  is  then  dissolved  in  a  few  c.c.  of  water,  acidified  with  nitric  acid, 
the  potassium  precipitated  with  20  c.c.  of  the  platinum  solution,  and  the 
volume  made  up  to  100  c.c.  with  alcohol  (95  per  cent.) ;  the  solution  is 
filtered,  and  50  c.c.  of  it  reduced  by  boiling  with  a  little  zinc,  again  made  up 
to  100  c.c.,  and  filtered ;  50  c.c.  of  this  filtrate  is  titrated  with  the  silver 
solution,  of  which,  say,  12  c.c.  are  required ;  then  12  c.c.  x  4  =  48  c.c., 
subtracted  from  160  c.c.,  represents  the  amount  of  chlorine  precipitated  as 
potassic  chloroplatinate  by  the  potassic  nitrate;  thus  (160—48)  c.c.  =  112  c.c. 
corresponds  to  0'5  gm.  of  potassic  nitrate,  i.e.,  to  0'232  K-O.  To  determine 
now  the  amount  of  potassium  in  any  salt  the  process  just  described  is 
followed,  taking  10  c.c.  of  a  solution  containing  50  gm.  of  the  salt  per  liter. 
The  amount  of  chlorine  present  in  the  salt,  as  a  chloride,  must  be  determined 
by  titration,  and  allowed  for  before  calculating  the  amount  of  potassium. 
Thus,  if  the  10  c.c.  of  the  solution  (i.e.,  0'5  gm.  of  the  sample)  required 
8  c.c.  of  the  silver  solution  and  27  c.c.  were  required  of  it  after  the  reduction 
with  zinc,  the  calculation  would  be  (27  x  4 — 8)  c.c.  =  100  c.c.  and 

TOO  v  O'9^9 

-—— =  0'207  gm.  of    potash  in  0'5  gm.,  i.e.,  the  sample  contained 

41-40  per  cent,  of  K2O. 

This  process  has  been  critically  examined  under  the  direction  of 
Dr.  Wiley  (C.  N.  liii.  176),  who  states,  that  owing  to  uncertainty 
in  estimating  the  chlorine,  the  conclusions  are  not  satisfactory. 
This  has  given  me  no  difficulty  when  using  potassic  chromate 
as  indicator,  taking  the  precaution  to  add  a  little  pure  calcic 
carbonate  to  insure  neutrality.  It  has  given  me  good  approximate 
results  with  tolerably  pure  and  concentrated  potassium  salts,  viz., 
:iitrate,  sulphate,  and  chloride.  I  doubt  its  value  however  for 
estimation  of  small  percentages  of  potash  in  manures,  etc.  The 
process  is  rapid  and  easy,  but  care  should  be  taken  in  filtering  the 


§    16.  ALKALINE  SALTS.  59 

alcoholic  mixture  of  the  double  chloride  to  avoid  loss  by  evaporation 
before  measuring.  The  solutions  precipitated  by  zinc  need  no 
filtering,  as  they  settle  rapidly.  ^  silver  solution  is  available  for 
the  clilorine  estimation ;  the  weak  point  in  the  process  is  probably 
due  to  the  strong  saline  liquids  affecting  the  delicacy  of  the 
chromate  indicator. 


TECHNICAL    EXAMINATION    OF    SOME    ALKALINE 

COMPOUNDS    FOUND     IN    COMMERCE     OB    OCCURRING    IN 

COURSE    OF    MANUFACTURE. 

There  is  now  considerable  unanimity  among  English  and  foreign 
manufacturers  of  alkaline  compounds,  as  to  methods  of  analysis  to 
be  adopted  either  for  guidance  in  manufacture  or  commercial 
valuation.  Lunge  has  contributed  important  papers  on  the 
subject  (/.  S.  C.  I.  i.  12,  16,  55,  92),  also  in  conjunction  with 
Hurter  in  the  Alkali  Makers'  Pocket  Book*  which  contains 
valuable  tables  and  processes  of  analysis.  So  far  as  volumetric 
methods  are  concerned,  the  same  processes  will  be  given  here  with 
others. 

14.     Soda   Ash,    Black  Ash,   Mother-liquors,    etc. 

Soda  Ash  or  Refined  Alkali. — 5  or  10  gm.  are  dissolved  in  about  150  c.c. 
of  warm  distilled  water,  and  any  insoluble  matter  filtered  off  (German 
chemists  do  not  filter),  and  the  volume  diluted  to  ^  or  1  liter. 

The  total  quantity  of  alkali  is  determined  in  50  c.c.  by  normal  sulphuric, 
nitric,  or  hydrochloric  acid,  as  in  §  16.  l.f 

The  quantity  of  caustic  alkali  present  in  any  sample  is  determined  as 
in  §  16.  2  or  5. 

The  presence  of  sulphides  is  ascertained  by  the  smell  of  sulphuretted 
hydrogen  when  the  alkali  is  saturated  with  an  acid,  or  by  dipping  paper 
steeped  in  sodic  nitro-prusside  into  the  solution :  if  the  paper  turns  blue  or 
violet,  sulphide  is  present. 

The  quantity  of  sulphide  and  sulphite  may  be  determined  by  saturating 
a  dilute  solution  of  the  alkali  with  a  slight  excess  of  acetic  acid,  adding  starch 
and  titrating  with  -f^  iodine  solution  till  the  blue  colour  appears.  The 
quantity  of  iodine  required  is  the  measure  of  the  sulphuretted  hydrogen 
and  sulphurous  acid  present. 

The  proportion  of  sulphide  is  estimated  as  follows  : — 13'820  gm.  of  pure 
silver  are  dissolved  in  dilute  nitric  acid,  and  the  solution,  together  with  an 
excess  of  liquid  ammonia,  made  up  to  a  liter.  Each  c.c.  =0'005  gm.  Na2S. 

The  Analysis :  100  c.c.  of  the  alkali  liquor  is  heated  to  boiling,  some 
ammonia  added,  and  the  silver  solution  dropped  in  from  a  burette  until  no 
further  precipitate  of  A^S  is  produced.  Towards  the  end  filtration  will  be 
necessary,  in  order  to  ascertain  the  exact  point,  to  which  end  the  Beales 
filter  is  serviceable  (fig.  19).  The  amount  of  Na2S  so  found  is  deducted 
from  the  total  sulphide  and  sulphite  found  by  iodine. 

Sodic  chloride  (common  salt)  may  be  determined  by  carefully  neutralizing 
1  gm.  of  the  alkali  with  nitric  acid,  and  titrating  with  decinormal  silver 

*  Bell  &  Sons,  York  Street,  Covent  Garden. 

t  This  gives  a  slight  error,  owing  to  traces  of  aluminate  of  soda  and  lime,  which 
consume  acid. 


60  VOLUMETRIC  ANALYSIS.  §    16. 

solution  and  potassic  chromate.  Each  c.c.  represents  0'005837  gm.  of 
common  salt.  Since  the  quantity  of  acid  necessary  to  neutralize  the  alkali 
has  already  been  found,  the  proper  measure  of  ^  nitric  acid  may  at  once 
be  added. 

Sodic  sulphate  is  determined,  either  directly  or  indirectly,  as  in  §  73. 
Each  c.c.  or  dm.  of  normal  baric  chloride  is  equal  to  0'071  gm.  or  0'7l  grn. 
of  dry  sodic  sulphate. 

Examination  of  Crude  Soda  Lyes  and  Red  Liquors.  —  Kalmann 
and  Spuller  (Dingl.  polyt.  J.}  264,  456  —  459)  recommend  a  process  based 
on  the  insolubility  of  baric  sulphite  and  the  solubility  of  baric  thiosulphate 
in  alkaline  solutions.  The  estimation  is  performed  in  the  following 
manner:  —  1.  —  The  total  alkalinity  is  determined  in  a  measured  volume  of 
the  liquor  under  examination  by  titration  with  normal  acid,  methyl  orange 
being  used  as  indicator.  The  acid  consumed  equals  sodic  carbonate  +  sodic 
sulphide,  +  sodic  hydroxide,  +  one-half  sodic  sulphite  (Na'-SO3  is  alkaline 
and  NaHSO3  neutral  to  methyl  orange).  2.  —  An  equal  volume  of  the 
liquor  is  titrated  with  ^  solution  of  iodine,  the  volume  consumed  corres- 
ponding with  the  sodic  sulphide  +  the  sodic  sulphite,  +  the  sodic 
thiosulphate.  3.  —  Twice  the  volume  of  liquor  as  that  used  in  (1)  and  (2) 
is  precipitated  with  an  alkaline  zinc  solution,  and  the  mixture  made  up  to 
a  certain  measure,  one-half  of  which  is  filtered,  acidified,  and  titrated  with 
Y^  iodine.  The  iodine  consumed  equals  sodic  sulphite  +  sodic  thiosulphate. 
4.  —  Three  or  four  times  the  volume  of  liquor  used  in  (1)  and  (2)  is  treated 
with  an  excess  of  a  solution  of  baric  chloride,  the  mixture  made  up  to 
a  known  volume  with  water,  and  filtered,  (a.)  One-third  or  one-fourth 
(as  the  case  may  be)  of  the  filtrate  is  titrated  with  normal  acid,  the  amount 
used  corresponding  with  the  sodic  hydroxide  +  the  sodic  sulphite. 
(b.)  A  new  third  or  fourth  of  the  filtrate  is  acidified  and  titrated  with  ^ 
iodine,  the  iodine  consumed  being  equal  to  sodic  sulphite  +  sodic  thio- 
sulphate. The  calculation  is  made  as  follows  :  — 

2   —  45  .........  =  A  c.c.  j^-  iodine  corresponding  to  ......  Na2S03 

2   —  3    .........  —  B  c.c.  ^  iodine  corresponding  to  ......  Na2S 

46  —  (2—3)    .  .  .  =  C  c.c.  T*V  iodine  corresponding  to  ......  Na2S203 

4a  —  TVB    ......  =  D  c.c.  normal  acid  corresponding  to  ...  NaOH 

1   —  (4a  +  TVA)  =  E  c.c.  normal  acid  corresponding  to  ...  Na2CO3 


Black  Ash.  —  Digest  50  gm.  with  warm  water  in  a  i  liter  flask,  fill  up  to 
mark,  and  allow  to  settle  clear. 

(1)  Total  Alkali  existing  as  carbonate,  hydrate,  and  sulphide,  is  found  by 
titrating  10  c.c.  =  l  gm.  of  ash  with  standard  acid  and  methyl  orange  in  the 
cold. 

(2)  Caustic  Soda.—  20  c.c.  of  the  liquid  is  put  into  a  100  c.c.  flask  with 
10  c.c.  of  solution  of  baric  chloride  of  10  per  cent,  strength,  filled  up  with 
hot  water,  well  shaken,  and  corked  after  settling  a  few  minutes.     The  clarified 
liquid  is  filtered,  and  50  c.c.  =  l  gm.  ash,  titrated  with  standard  acid  and 
methyl  orange;  or  it  may  be  titrated  without  filtration  if  standard  oxalic 
acid  and  phenolphthalein  are  used,  this  acid  having  no  effect  on  the  baric 
carbonate.     Each  c.c.  normal  acid  =  0'031  Na2O.     This  includes  sulphides. 

(3)  Sodic  Sulphide.  —  Put  10  c.c.  of  liquor  into  a  flask,  acidulate  with 
acetic  acid,  dilute  to  about  200  c.c.  and  titrate  with  ^  iodine  and  starch. 
Each  c.c.  =  0-0039  Na2S,  or  0'0031  Na2O. 

(4)  Sodic  Chloride.  —  10  c.c.  are  neutralized  exactly  with  normal  nitric 
acid,  and  boiled  till  all  H2S  is  evaporated.     Any  sulphur  which  may  have 
been  precipitated  is  filtered  off,  and  the  filtrate  titrated  with  ^  silver  and 
chromate.     Each  c.c.  =  0'005837  gm.  NaCl. 

(5)  Sodic  Sulphate.  —  This  is  best  estimated  by  precipitation  as  baric 
sulphate,  and  weighing,  the  quantity  being  small.     If,  however,  volumetric 
estimation  is  desired,  it  may  be  done  as  in  §  73,  taking  50  c.c.  of  liquor. 


§    1G.  ALKALINE   COMPOUNDS.  61 

For  other  methods  of  examining  the  various  solid  and  liquid 
alkali  wastes  used  for  soda  and  sulphur  recovery,  etc.,  the  reader  is 
referred  to  the  Alii  all  Makers'  Pocket  Bool-  already  mentioned. 

15.     Salt    Cake 

Is  the  impure  sodic  sulphate  used  in  alkali  manufacture  or  left  in 
the  retorts  in  preparing  hydrochloric  acid  from  sulphuric  acid  and 
salt,  or  nitric  acid  from  sodic  nitrate.  It  generally  contains  free 
sulphuric  acid  existing  as  sodic  bisulphate,  the  quantity  of  which 
may  be  ascertained  by  direct  titration  with  normal  alkali. 

The  common  salt  present  is  estimated  by  decinormal  silver  solution  and 
chromate;  having  first  saturated  the  free  acid  with  pure  sodic  carbonate, 
1  c.c.  or  1  dm.  silver  solution  is  equal  to  0'005837  gm.  or  0'05837  grn.  of  salt. 

Sulphuric  acid,  combined  with  soda,  is  estimated  either  directly  or 
indirectly  as  in  §  73 ;  1  c.c.  or  1  dm.  of  normal  baryta  solution  is  equal  to 
0'07l  gm.  or  0'71  grn.  of  dry  sodic  sulphate. 

Iron  is  precipitated  from  a  filtered  solution  of  the  salt  cake  with  ammonia 
in  excess,  the  precipitate  of  ferric  oxide  re-dissolved  in  sulphuric  acid, 
reduced  to  the  ferrous  state  with  zinc  and  titrated  with  permanganate. 

Grossman  adopts  a  method  suggested  by  Bohlig  (see  §  28), 
and  has  worked  out  the  process  in  the  case  of  salt  cake  in  careful 
detail  (C.  N.  xli.  114)  as  follows  :— 

The  neutral  solution  of  salt  cake  (3'55  gm.)  is  put  into  a  500  c.c. 
flask,  250  c.c.  of  a  cold  saturated  solution  of  baric  hydrate  added, 
the  flask  filled  with  water,  and  shaken  up.  Of  the  filtered  clear  liquid 
250  c.c.  are  put  in  an  ordinary  flask,  carbonic  acid  passed  through 
for  about  ten  minutes,  and  then  the  contents  of  the  flask  boiled  so 
as  to  decompose  any  baric  bicarbonate  which  may  be  in  solution.  After 
cooling,  the  contents  of  the  flask  are  again  transferred  to  the  500  c.c. 
flask,  the  latter  filled  up  with  water  to  the  mark,  shaken  up,  and  filtered. 
250  c.c.  of  the  filtrate — i.e.,  one-fourth  of  the  original  quantity  used — are 
then  titrated  with  one-fourth  normal  sulphuric  acid.  The  number  of  c.c.  of 
one-fourth  normal  acid  used  multiplied  by  two  will  give  the  percentage  of 
sodic  sulphate. 

There  are,  however,  sources  of  error  in  the  experimental  working  of  this 
method  which  make  certain  corrections  necessary.  They  arise — 

(1)  Prom  the  impurities  of  the  caustic  baryta. 

(2)  From  the  precipitate  formed  in  the  measured  liquid. 

(3)  From  certain  constant  losses. 

The  commercial  caustic  baryta  always  contains  baric  nitrate,  and  sometimes 
baric  chloride.  It  is  evident  that  on  adding  a  solution  of  baric  hydrate 
which  contains  baric  nitrate  to  a  solution  of  sodic  sulphate,  a  quantity  of  the 
latter,  equivalent  to  the  quantity  of  the  baric  nitrate  present,  will  be 
converted  into  sodic  nitrate,  and  thus  escape  the  alkalimetric  test,  as  will  be 
seen  by  the  following  equations : — 

Ba(N03)2+Na2S04=BaS04+2NaNO3. 
Ba(N03)2+2NaOH+C02=BaCO3+2NaN03+H20. 

It  is  therefore  necessary  to  measure  approximately  the  quantity  of  baryta 
solution  used,  so  as  to  know  the  amount  of  baric  nitrate  introduced  into  the 
process.  The  latter  can  be  easily  ascertained  by  passing  carbonic  acid  in 
excess  through  the  cold  saturated  solution  of  baric  hydrate,  boiling,  filtering, 
and  precipitating  the  baryta  left  in  solution  by  sulphuric  acid  as  usual. 


62  VOLUMETRIC  ANALYSIS.  §    16. 

250  c.c.  of  a  baryta  solution  used  for  experiment  yielded  0"0280  gin.  BaSO4, 
which  corresponds  to  0'0l7l  gm.  Na2SO4,  or  0"96  c.c.  of  one-fourth  normal 
acid ;  and  it  follows  that  for  every  250  c.c.  of  this  baryta  solution  was  found 
O'OIYI  gm.  Na2SO4  too  little;  or,  that  there  must  be  added  0'24  c.c.  of 
one-fourth  normal  acid  to  the  result  of  the  final  tilration  (of  one-fourth  of 
the  original  quantity).  If  the  baryta  contain  caustic  alkali,  a  corresponding 
quantity  of  baric  nitrate  will  be  found  less  by  the  test;  but  it  is  easily 
understood,  that  the  calculations  will  not  be  influenced  as  long  as  the  baric 
nitrate  is  in  excess  of  the  caustic  alkali,  which  is  always  the  case  in  good 
commercial  baryta. 

The  second  error  arises  from  the  precipitates  of  baric  sulphate  and  carbonate 
taking  up  some  space  in  the  500  c.c.  flask,  the  final  results  thus  being  found 
too  high.  If  it  is  assumed  that  a  cold  saturated  solution  of  baryta  contains 
about  23  gm.  BaO  per  liter,  it  will  be  near  enough  for  all  practical  purposes 
if  in  the  experiment,  working  with  3"55  gm.  of  Na2SO4  and  250  c.c.  of  baryta 
solution,  0"4  per  cent,  is  subtracted  from  the  final  results  for  this  error. 

Three  experiments  made  with  3' 55  gm.  of  pure  ignited  sodic  sulphate  gave 
the  following  results : — 

Used  one-fourth  normal  acid    ...     49"37  c.c. 
Add  for  Ba(NO3)2      0'24  c.c. 

49'61  c.c. 
=  99'22  per  cent.  Na2SO4. 

II. 

Used  one-fourth  normal  acid    ...     49'21  c.c. 
Add  for  Ba(N03)2       0'24  c.c. 


49-45  c.c. 
=98-90  per  cent.  Na2S04. 

III. 

Used  one-fourth  normal  acid    ...     49'37  c.c. 
Add  for  Ba(NO3)2       0'24  c.c. 


49-61  c.c. 
=  99*22  per  cent.  Na2S04. 

The  average  of  these  three  experiments  gives  99'1  per  cent. ;  and  if  0'4 
per  cent,  be  subtracted  for  the  precipitate,  the  result  is  98'7  per  cent,  instead 
of  100. 

Grossman  states  that  this  loss  of  T3  per  cent,  in  working  with  3'55  gm. 
of  sulphate  in  the  given  dilution  is  a  constant,  and  by  dividing  all  results  by 
0*987  correct  results  are  obtained. 

It  now  remains  to  show  the  applicability  of  this  method  to  the  assay  of 
salt  cake  and  like  substances.  The  following  is  a  complete  analysis  of  a 
sample  of  salt  cake  made  in  the  usual  way : — 

Moisture     0'49 

Insoluble     0'29 

Free  sulphuric  hydrate     0"38 

Aluminium  sulphate 0"23 

Ferric  sulphate . . .'  0'42 

Calcic  sulphate 1*17 

Sodic  chloride     2'00 

Sodic  sulphate  (by  difference) 95'02 

100-00 


§    16.  ALKALINE   COMPOUNDS.  63 

In  order  to  make  a  good  analysis  of  salt  cake  by  weight  it  is  necessary  to 
estimate  seven  constituents,  to  find  by  difference  the  quantity  of  actual  sodic 
sulphate,  which  is  the  only  constituent  wanted. 

When  baric  hydrate  is  added  to  a  solution  of  salt  cake  the  free  acid  is 
precipitated,  so  are  alumina  and  iron,  and  the  sulphuric  acid  combined  with 
them  and  with  lime.  The  lime  is  partly  thrown  down  as  such,  and  what  is 
left  as  lime  in  solution  is  precipitated  as  carbonate  in  the  second  operation. 
Thus,  whatever  other  sulphates  be  present,  only  the  sodic  sulphate  is  given  ; 
and  by  one  simple  test  we  are  thus  able  to  get  a  result  which  formerly  could 
only  be  attained  by  a  tedious  complete  analysis. 

The  salt  cake,  of  which  a  complete  analysis  is  given  above,  was  tested  by 
the  alkalimetric  method.  3' 5  5  gm.  required — 

One-fourth  normal  acid     46*95  c.c. 

Add  for  Ba(NO3)2      0'24  c.c. 


47*19  c.c. 
=94-38  per  cent.  Na2SO4. 

(94-38— 0-40) -=93-98. 

93-98  :  0-987=95-2  per  cent.  Na2SO4. 

Thus,  by  the  alkalimetric  test,  95 -2  per  cent.  Na2S04  occurs, 
whereas  the  analysis  gives  95 -02  per  cent.  If  it  be  considered  how 
difficult  it  is  to  wash  soda  salts  completely  from  precipitates,  it  is 
not  surprising  to  find  the  result  too  low  in  the  complete  analysis, 
as  in  five  precipitates  a  very  minute  quantity  will  make  up  0*2 
per  cent. 

It  is  hardly  necessary  to  point  out  that  none  of  the  figures  for 
the  correction  of  the  errors  enumerated  above  can  be  used  by  any 
one  else  working  by  this  method,  but  that  they  must  be  ascertained 
in  every  individual  case.  It  is  absolutely  necessary  -to  ascertain 
after  the  first  operation  that  there  is  no  sulphate,  and  after  the 
second  (before  titrating)  that  there  is  no  baryta  in  solution. 

16.     Raw    Salt,    Brine,    etc. 

Lime  may  be  estimated  by  precipitation  with  ammonic  oxalate,  and  the 
precipitate  titrated  with  permanganate,  as  in  §  48. 

Sulphuric  acid  as  in  §  73. 

Magnesia  is  precipitated  as  ammoniacal  phosphate,  by  a  solution  of  sodic 
phosphate  containing  ammonia,  first  removing  the  lime  by  ammonic  oxalate, 
the  precipitate  of  double  phosphate  of  magnesia  and  ammonia  is  brought  on 
a  filter,  washed  with  cold  water  containing  ammonia,  then  dissolved  in  acetic 
acid,  and  titrated  with  standard  uranium  solution,  or  by  the  process  for 
P205  (§  23-2). 

The  quantity  of  real  salt  in  the  sample  may  be  ascertained  by  treating  a 
weighed  quantity  in  solution  with  caustic  baryta,  boiling,  setting  aside  that 
the  excess  of  baryta  may  precipitate  itself  as  carbonate,  or  more  quickly  by 
adding  ammonic  carbonate,  filtering,  evaporating  the  solution  to  dryness,  and 
gently  igniting — the  residue  is  pure  salt.  The  loss  of  weight  between  this 
and  the  original  specimen  taken  for  analysis,  will  show  the  percentage  of 
impurities. 

17.     Silicates    of   Soda    and   Potash. 
A  weighed  quantity  of  the  substance  is  gently  ignited,  until  no  aqueous 


64  VOLUMETRIC   ANALYSIS.  §    16. 

vapours  are  given  off,   and  the  residue  weighed — thus  the  respective  per- 
centages of  water  and  anhydrous  material  are  obtained. 

Another  portion  of  the  substance  is  dissolved  in  hot  water,  and  titrated 
with  litmus  and  normal  acid  boiling,  or  with  methyl  orange  after  cooling.  The 
volume  of  acid  is  calculated  to  soda  br  potash.  Solid  alkaline  silicates  require 
to  be  finely  powdered  previous  to  solution  in  hot  water. 

18.     Soap. 

The  methods  here  given  are  a  combination  of  those  published 
by  A.  R.  Leeds  (C.  N.  xlviii.  166)  and  C.  R.  A.  Wright  (Journ. 
Soc.  Arts,  1885,  1117,  also  J.  S.  C.  I.  iv.  631). 

(1)  Moisture  and   Volatile  Matters. — 15  gm.  are  dried  to  a  constant 
weight,  first  at  100°,  then  at  120°  C. 

(2)  Free  Fats. — Residue  of  1  is  exhausted  with  light  petroleum  ether, 
and  the  extract,  after  evaporation  of  the  ether,  weighed. 

(3)  Fatty    Acids,    Chlorides,    Sulphates,    Glycerine,   etc. — The    residue 
from  (2),  which  has  been  treated  with  ether,  represents  15  gm.  soap ;  it  is 
weighed,  und  two-thirds  of  it  are  dissolved  in  water,  and  normal  nitric  acid 
added  in  excess  to  separate  the  fatty  acids.     These  are  collected  on  a  tared 
filter,  dried,  and  weighed.     The  acid  filtrate  is  now  titrated  with  normal  soda 
or  potash  (free  from  chlorides  or  sulphates),  with  phenolphthalein  as  indicator; 
the  difference  between  the  volumes  of  acid  and  alkali  used  gives  roughly  the 
total  alkali.     The  residual  neutral  liquid  is  divided  into  two  equal  parts,  in 
one  of  which  chlorine  is  estimated  with  &  silver  and  chromate,  and  in  the 
other  sulphuric  acid  by  normal  baric  chloride.     If   glycerine  is  present, 
it  may  be  estimated  by  Muter 's  copper  test  in  the  absence  of   sugar. 
Sugar  is,  however,  often  largely  used   in  transparent  soaps  in  place  of 
glycerine :  when  both  are  present,  the  separate  estimation  is  difficult,  but 
Wright  suggests  the  method  of  Fehling  for  the  sugar,  first  inverting 
with  acid ;  the  copper  retained  in  solution  by  the  glycerine  being  estimated 
colorimetrically,  using  for  comparison  a  liquid  containing  both  sugar  and 
glycerine  to  known  extents,  treated  side  by  side  with  the  sample  tested. 

(4)  Free  and  Total  Alkali. — These  are  obtained  by  Wright's  alcohol  test. 
Two  or  three  grams  of  the  soap  is  boiled  with  95  per  cent,  alcohol,  the  extract 
filtered  off  and  residue  washed  with  alcohol.     The  solution  so  obtained  may 
be  either  positively  alkaline  with  caustic  alkali,  or  negatively  alkaline  from 
the  presence  of  fatty  acids  or  a  diacid  soap,  according  to  the  kind  of  soap 
used.     Phenolphthalein  is  added,  which  shows  at  once  whether  free  alkali  is 
present,  and  in  accordance  with  this  either  standard  alcoholic  acid  or  alkali  is 
used  for  titration.     The  residue  on  the  filter  is  then  dissolved  in  water,  and 
titrated  with  normal  or  decinormal  acid ;  the  alkali  so  found  may  include 
carbonate,  silicate,  borate,  or  aluminate  of   soda  or  potash,  and  also  any 
soluble  lime.     The  sum  of  the  two  titrations  will  be  the  total  alkalinity  in 
case  both  showed  an  alkaline  reaction ;    if   otherwise,   the  alkali  used  to 
produce  a  colour  in  the  alcoholic  extract  is  deducted  from  the  volume  of  acid 
used  in  the  water  extract.     This  method  of  taking  the  alkalinity  of  a  soap 
is  very  fairly  exact ;   the  error  ought  never  to  exceed   +_  0'5  per  cent. 
Wilson  (C.  N.  lix.  280)  states  that  the  estimation  of  free  caustic  alkali  in 
high  class  soaps,  containing  no  free  glycerides,  by  the  alcoholic  method  is 
correct,  but    in  the    case    of    common    commercial  soaps    it  is    entirely 
misleading. 

The  method  of  C.  Hope  is  undoubtedly  the  quickest  and  best  for  the 
examination  of  the  alcoholic  solution  of  soap.  Two  grams  of  soap  is  dissolved 
in  hot  absolute  alcohol,  a  drop  of  phenolphthalein  indicator  added,  and  some 
bubbles  of  CO2  passed  through  till  the  colour  disappears.  The  liquid  is 
filtered ;  the  residue,  consisting  of  total  impurities,  is  washed  with  hot  alcohol, 


§    17.  ALKALINE    EARTHS.  65 

weighed  and  titrated  with  T\  acid  and  methyl  orange,  which  gives  the  alkali 
not  existing  as  soap.  The  alcoholic  solution  is  evaporated  to  dryness  at 
100°  C.  and  the  dry  soap  weighed.  It  is  then  gently  ignited,  dissolved  in 
water,  and  titrated  with  T^-  acid  and  methyl  orange  to  find  the  alkali  existing 
as  soap.  The  difference  between  this  and  the  soap  residue,  before  ignition, 
gives  the  fatty  anhydrides,  which  multiplied  by  1'03  gives  the  fatty  acids. 
The  water  is  found  by  deducting  the  weights  of  the  impurities  and  dry  soap 
from  100.  Fuller  information  on  this  subject  may  be  found  in  Allen's 
Organic  Analysis  and  in  Lant  Carpenter's  treatise  on  Soap  and  Candles. 

TITBATION    OF    ALKALINE    EARTHS. 

§  17.  STANDARD  hydrochloric  or  nitric  acid  must  in  all  cases  be 
used  for  the  titration  of  the  caustic  or  carbonated  alkaline  earths,  as 
these  are  the  only  acids  yielding  soluble  compounds,  except  in  the 
case  of  magnesia.  The  hydrates,  such  as  caustic  lime,  baryta, 
strontia,  or  magnesia,  may  all  be  estimated  by  any  of  the  indicators, 
using  the  residual  method,  i.e.,  adding  a  known  excess  of  standard 
acid,  boiling  to  expel  any  trace  of  CO2,  and  re-titrating  with 
standard  alkali. 

The  carbonates  of  the  same  bases  may  of  course  also  be 
estimated  in  the  same  way,  bearing  in  mind,  that  when  methyl 
orange  is  used,  the  liquid  is  best  cooled  before  re-titration.  All 
heating  may  be  avoided  when  using  methyl  orange  in  titrating 
mixtures  of  hydrates  and  carbonates,  or  the  latter  only,  unless  it  is 
impossible  to  dissolve  the  substance  in  the  cold.  A  good  excess 
of  acid  is  generally  sufficient. 

The  total  amount  of  base  in  mixtures  of  caustic  and  carbonated 
alkaline  earths  is  also  estimated  in  the  same  way. 

(1)  Estimation  of  Mixed  Hydrates  and  Carbonates. — This  may 
be  done  either  by  phenacetolin  or  phenolphthalein  as  indicator. 
The  former  has  been  recommended  by  Degener  and  Lunge  :  the 
method,  however,  requires  practice  in  order  to  mark  the  exact 
change  of  colour. 

The  liquid  containing  the  compound  in  a  fine  state  of  division  is  tinted 
with  the  indicator  so  as  to  be  of  a  faint  yellow ;  standard  acid  is  then 
cautiously  added  until  a  permanent  pink  occurs  (at  this  stage  all  the  hydrate 
is  saturated),  more  acid  is  now  cautiously  added  until  the  colour  becomes  deep 
yellow,  the  volume  of  acid  so  used  represents  the  carbonate. 

The  method  is  especially  adapted  to  mixtures  of  calcic  hydrate 
and  carbonate.  It  is  also  applicable  to  barium,  but  not  to 
magnesium,  owing  to  the  great  insolubility  of  magnesic  hydrate  in 
dilute  acid.  If  phenolphthalein  is  used  as  indicator,  the  method  is 
as  follows  : — 

Heat  the  liquid  to  boiling,  and  cautiously  add  standard  acid  until  the  red 
colour  is  just  discharged.  The  carbonates  of  lime  and  baryta,  rendered 
dense  by  boiling,  are  both  quite  neutral  to  the  indicator.  To  obtain  the 
whole  of  the  base,  excess  of  standard  acid  is  used,  and  the  mixture  re-titrated 
with  standard  alkali. 


66  VOLUMETRIC  ANALYSIS.  §    17. 

Magnesia  in  solution  as  bicarbonate  may  be  accurately  estimated 
in  the  cold  with  methyl  orange  as  indicator. 

(2)  Estimation  of  Calcium,  Barium,  and  Strontium  in  Neutral 
Soluble  Salts. — The  amount  of  base  in  the  chlorides  and  nitrates  of 
these  alkaline  earths  may  be  readily  estimated  as  follows : — 

The  weighed  salt  is  dissolved  in  water,  cautiously  neutralized  if  acid  or 
alkaline,  phenolphthalein  added,  heated  to  boiling,  and  standard  sodic 
carbonate  delivered  in  from  time  to  time  \\lth  boiling  until  the  red  colour  is 
permanent. 

Magnesium  salts  cannot  however  be  estimated  in  this  way, 
or  even  mixtures  of  lime  and  magnesia,  as  magnesic  carbonate 
affects  the  indicator  in  a  different  manner  to  the  other  carbonates. 

(3)  Precipitation  of  the  Alkaline  Earths  from  their  Neutral  Salts  as 
Carbonates. — Soluble  salts  of  lime,  baryta,  and  strontia,  such  as  chlorides, 
nitrates,  etc.,  are  dissolved  in  water,  and  the  base  precipitated  as  carbonate, 
with  excess  of  ammonic  carbonate  and  some  free  ammonia.     The  mixture  is 
heated  to  about  60°  C.  for  a  few  minutes.    The  precipitated  carbonate  is  then 
to  be  filtered,  well  washed  with  hot  water  till  all  soluble  matters,  especially 
ammonia,  are  removed,  and  the  precipitate  with  filter  titrated  with  normal 
acid,  as  already  described. 

Magnesia  salts  require  caustic  soda  or  potash  instead  of  ammonic  carbonate ; 
but  the  process  gives  results  slightly  too  low,  owing  to  the  slight  solubility  of 
magnesic  hydrate  in  the  alkaline  liquid. 

(4)  Lime  and  Magnesia  Carbonates  in  Waters. — The  amount  of  calcic, 
or  calcic  and  magnesic  carbonates,  dissolved  in  ordinary  non-alkaline  waters 
may  be  very  readily,  and  with  accuracy,  found  by  taking  200  or  300  c.c. 
of  the  water,  heating  to  near  boiling,  adding  phenacetolin  or  lacmoid,  and 
titrating  cautiously  with  yV  nitric  or  sulphuric  acid.    An  equally  accurate 
result  may  be  obtained  by  methyl  orange  in  the  cold  liquid. 

(5)  Hardness  of  "Water  estimated  without  Soap  Solution. — As  is 
generally  known,  the  soap-destroying  power  of  a  water  is  ascertained 
in  Clark's  process  by  a  standard  solution  of  soap  in  weak  alcohol, 
titrated    against    a    standard    solution    of    calcic    chloride.       The 
valuation  is  in  so-called  degrees,  each  degree  being  equal  to  1  grain 
of  calcic  carbonate,  or  its  equivalent,  in  the  imperial  gallon.     The 
process  is  an  old  and  familiar  one,  but  open  to  many  objections 
from  a  scientific  point  of  view.     The  scale  of  degrees  is  arbitrary, 
and    is    seriously    interfered    with    by   the    presence   of    varying 
proportions  of  magnesia. 

We  are  indebted,  primarily  to  Mohr,  and  subsequently  to 
Hehner,  for  an  ingenious  method  of  determining  both  the 
temporary  and  permanent  hardness  of  a  water  without  the  use 
of  soap  solution. 

The  standard  solutions  required  are  -j^  sodic  carbonate  and 
-T^J-  sulphuric  acid.  Each  c.c.  of  standard  acid  exactly  neutralizes 
1  m.gm.  of  CaCO3,  and  each  c.c.  of  the  alkali  precipitates  the  like 
amount  of  CaCO3,  or  its  equivalent  in  magnesia,  in  any  given 
water. 


§    18.  AMMONIA.  67 

The  Analysis :  100  c.c.  of  the  water  is  tinted  with  an  indicator  of  suitable 
character,  heated  to  near  boiling,  and  standard  acid  cautiously  added  until 
the  proper  change  of  colour  occurs.  Hehner  recommends  phenacetolin ; 
but  my  own  experiments  give  the  preference  to  lacmoid,  which  is  also 
commended  by  Thompson.  Draper  (C.  N.  li.  206)  points  out  the  value 
of  lacmoid  and  carminic  acid  for  such  a  process,  and  I  fully  endorse  his 
opinion  with  respect  to  both  indicators.  Practice  is  desirable  in  order 
to  recognize  the  precise  .end-reaction.  The  number  of  c.c.  of  acid  used 
represents  the  number  of  Clark's  degrees  of  temporary  hardness  per  100,000. 
To  obtain  degrees  per  gallon,  multiply  the  number  of  c.c.  by  O'V.  The 
permanent  hardness  is  ascertained  by  taking  100  c.c.  of  the  water  and  adding 
to  it  a  rather  large  known  excess  of  the  standard  sodic  carbonate.  The 
quantity  must  of  course  be  regulated  by  the  amount  of  sulphates,  chlorides, 
or  nitrates  of  lime  and  magnesia  present  in  the  water ;  as  a  rule,  a  volume 
equal  to  the  water  will  more  than  suffice.  Evaporate  in  a  platinum  dish  to 
dry  ness  (glass  or  porcelain  will  not  do,  as  they  affect  the  hardness),  then 
extract  the  soluble  portion  with  small  quantities  of  distilled  water,  through 
a  very  small  filter,  and  titrate  the  filtrate  with  the  standard  acid  for  the 
excess  of  sodic  carbonate  :  the  difference  represents  the  permanent  hardness. 

Some  waters  contain  alkaline  carbonates,  in  which  case  there  is 
of  course  no  permanent  hardness,  because  the  salts  to  which  this  is 
due  are  decomposed  by  the  alkaline  carbonate.  In  examining  a 
water  of  this  kind,  the  temporary  hardness  will  be  shown  to  be 
greater  than  it  really  is,  owing  to  the  alkaline  carbonate ;  and  the 
estimation  for  permanent  hardness  will  show  more  sodic  carbonate 
than  was  actually  added.  If  the  difference  so  found  is  deducted 
from  the  temporary  hardness,  as  first  noted,  the  remainder  will  be 
the  true  temporary  hardness. 


AMMONIA. 


§  18.  IN  estimating  the  strength  of  solutions  of  ammonia  by  the 
alkalimetric  method,  it  is  better  to  avoid  the  tedious  process  of 
weighing  any  exact  quantity,  and  to  substitute  for  it  the  following 
plan,  which  is  applicable  to  most  liquids  for  the  purpose  of 
ascertaining  both  their  absolute  and  specific  weights. 

Let  a  small  and  accurately  tared  flask,  beaker,  or  other  convenient  vessel 
be  placed  upon  the  balance,  and  into  it  10  c.c.  of  the  ammoniacal  solution 
delivered  from  a  very  accurately  graduated  10  c.c.  pipette.  The  weight 
found  is,  of  course,  the  absolute  weight  of  the  liquid  in  grams ;  suppose  it  to 
be  9'65  gm.,  move  the  decimal  point  one  place  to  the  left,  and  the  specific 
weight  or  gravity  is  at  once  given  (water  being  1),  which  in  this  case  is  0'965. 

It  must  be  borne  in  mind  that  this  system  can  only  be  used  properly  with 
tolerably  delicate  balances  and  very  accurate  pipettes.  The  latter  should 
invariably  be  tested  by  weighing  distilled  water  at  16°  C. 

The  10  c.c.,  weighing  9'65  gm.,  is  now  titrated  with  normal  acid,  of  which 
49  c.c.  are  required,  therefore  49  x  0'017=0-833  gm.  NH3=8'64  per  cent,  of 
real  ammonia;  according  to  Otto's  table  0'965  sp.  gr.  is  equal  to  8'50  per 
cent.  Ammonic  carbonate,  and  a  mixture  of  the  same  with  bicarbonate,  as 
it  most  commonly  occurs  in  commerce,  may  be  titrated  direct  with  normal 

F  2 


68  VOLUMETRIC   ANALYSIS.  §    18. 

acid  for  the  percentage  of  real  ammonia,  using  methyl  orange  as  indicator. 
The  carbonic  acid  can  be  determined  by  precipitating  the  solution  while  hot 
with  baric  chloride,  and  when  the  precipitate  is  well  washed,  dissolving  it 
with  an  excess  of  normal  acid  and  titrating  backward  with  normal  alkali ; 
the  number  of  c.c.  of  acid  used  multiplied  by  0'022  (the  |  mol.  wt.  of  CO2) 
will  give  the  weight  of  carbonic  acid  present  in  the  sample. 


1.    Estimation  of  Combined  Ammonia  by  distillation  with  Alkalies 
or  Alkaline  Earths. 

This  method  allows  of  the  expulsion  of  ammonia  from  all  its- 
salts.  Caustic  soda,  potash,  or  lime,  may  any  of  them  be  used 
where  no  organic  nitrogenous  compound  exists  in  the  substance  ; 
but  should  such  be  the  case,  it  is  preferable  to  use  freshly  ignited 
magnesia. 

The  distilling  apparatus  may  conveniently  be  arranged  by  con- 
necting an  ordinary  well-stoppered  small  retort  to  a  small  Liebig 
condenser,  and  leading  the  distilled  gas  into  a  vessel  containing  an 
excess  of  normal  acid.  After  the  operation  is  ended,  the  excess  of 
acid  is  ascertained  by  residual  titration  with  normal  alkali  or 
J  ammonia,  and  thus  the  amount  of  displaced  ammonia  is  found. 

The  retort  must  be  so  supported  that  its  neck  inclines  well 
upwards,  in  order  that  any  alkali  mechanically  carried  into  it  by 
the  spray  which  occurs  during  ebullition  shall  not  reach  the 
condenser.  An  angle  of  about  30°  suffices ;  and  in  order  that  a 
convenient  connection  may  be  made  with  the  condenser,  the  end  of 
the  retort  is  bent  downward,  and  the  connection  securely  made  with 
india-rubber  tubing.  In  like  manner,  the  end  of  the  condenser  is 
elongated  by  a  glass  tube  and  india-rubber  joint,  so  that  the  tube 
dips  into  a  two-necked  bottle  or  bulb,  containing  the  measured 
normal  acid;  the  end  of  this  tube  should  be  cut  obliquely,  and 
reach  nearly,-  but  not  quite,  to  the  surface  of  the  acid.  The  outlet 
of  the  receiver  is  fitted  with  a  tube  containing  glass  wool,  broken 
glass,  or  fibrous  asbestos,  Avetted  with  a  portion  of  the  normal 
acid,  so  that  any  traces  of  ammonia  which  may  possibly  escape 
condensation  in  the  bulk  of  the  acid  may  be  retained. 

The  retort  containing  the  ammoniacal  compound  in  solution 
being  securely  fixed,  and  all  the  apparatus  tightly  connected,  the 
stopper  of  the  retort  is  removed,  and  a  strong  solution  of  caustic 
alkali,  or,  in  case  of  compounds  in  which  ammonia  is  quickly 
released,  pieces  of  solid  alkali  are  rapidly  introduced,  the  stopper 
inserted,  and  the  distillation  forthwith  commenced.  Lime  or 
magnesia,  suspended  in  water,  must  be  added  through  a  small 
funnel ;  the  distillation  is  continued  until  the  steam  has  washed  all 
traces  of  ammonia  out  of  the  condenser  tube  into  the  normal  acid. 
Cold  water  is  of  course  run  continuously  through  the  condenser  as 
usual.  Finally,  the  tubes  connected  with  the  receiver  are  well 
washed  out  into  the  bulk  of  normal  acid,  methyl  orange  added,  and 
the  titration  completed  with  normal  alkali  or  f  ammonia. 


§ 


AMMONIA. 


69 


Each  c.c.  of  normal  acid  neutralized  by  the  displaced  ammonia 
represents  O'OIT  gni.  XH:5. 

The  apparatus  shown  in  fig.  23  is  of  great  value  in  determining 
accurately  all  the  forms  of  ammonia  which  can  be  displaced  by' 
soda,  potash,  or  lime,  and  the  gas  so  evolved  collected  in  a  known 
volume  in  excess  of  normal  acid,  the  excess  of  acid  being  after- 
wards found  by  residual  titration  with  normal  alkali  or  |  ammonia. 


Many  modifications  of  this  apparatus  have  been  suggested,  such 
as  the  introduction  of  a  condenser  between  the  two  flasks  to  cool 
the  distillate ;  another  is  the  use  of  a  U  tube  containing  some 
standard  acid  in  place  of  c.  I  do  not  find  that  any  of  these 
modifications  are  required  to  secure  accuracy,  if  the  apparatus  is 
tightly  fitted.  It  is,  however,  necessary  that  a  bulb  should  exist  in 
the  distilling  tube,  just  above  the  cork  of  the  distilling  flask, 
otherwise  I  have  found  that  the  spray  from  the  boiling  liquid 
Is  occasionally  projected  into  the  tube,  and  is  blown  over  with  the 
condensed  steam.  Another  precaution  is  advisable  where  dilute 


70  VOLUMETEIC  ANALYSIS.  §    18. 

liquids  are  boiled,  and  much  steam  generated,  that  is,  to  immerse 
the  condenser  flask  in  cold  water. 

The  little  flask,  holding  about  200  c.c.  and  placed  upon  the  wire 
gauze,  contains  the  ammoniacal  substance.  The  tube  d  is  filled  with  strong 
solution  of  caustic  potash  or  soda.  The  large  flask  holds  about  half  a  liter, 
and  contains  a  measured  quantity  of  normal  acid,  part  being  contained  in 
the  tube  c,  which  is  tilled  with  glass  wool  or  broken  glass,  and  through  which 
the  normal  acid  has  been  poured.  The  stoppers  of  the  flasks  should  be 
caoutchouc,  failing  which,  good  corks  soaked  in  melted  parafline  may  be  used. 

The  substance  to  be  examined  is  weighed  or  measured,  and  put  into  the 
distilling  flask  with  a  little  water,  the  apparatus  then  being  made  tight  at 
every  part ;  some  of  the  caustic  alkali  is  allowed  to  flow  in  by  opening  the 
clip,  and  the  spirit  lamp  is  lighted  under  it. 

The  contents  are  brought  to  gentle  boiling,  taking  care  that  the  froth,  if 
any,  does  not  enter  the  distilling  tube.  It  is  well  to  use  a  movable  gas 
burner  or  common  spirit-  lamp  held  under  the  flask  in  the  hand ;  in  case 
there  is  any  tendency  to  boil  over,  the  heat  can  be  removed  immediately,  and 
the  flask  blown  upon  by  the  breath,  which  reduces  the  pressure  in  a  moment. 
In  examining  guano  and  other  substances  containing  ammoniacal  salts  and 
organic  matter  by  this  means,  the  tendency  to  frothing  is  considerable ;  and 
unless  the  above  precautions  are  taken,  the  accuracy  of  the  results  will  be 
interfered  with. 

The  distilling  tube  has  both  ends  cut  obliquely;  and  the  lower  end  nearly, 
but  not  quite,  reaches  to  the  surface  of  the  acid,  to  which  a  little  methyl 
orange  may  be  added.  The  quantity  of  normal  acid  used  must,  of  course,  be 
more  than  sufficient  to  combine  with  the  ammonia  produced ;  the  excess  is- 
afterwards  ascertained  by  titration  with  normal  alkali  or  f  ammonia. 

It  is  advisable  to  continue  the  boiling  for  say  ten  or  fifteen  minutes,  then 
wait  a  minute  or  two  to  allow  all  the  ammonia  to  be  absorbed ;  then  opening 
the  clip,  blow  through  the  pipette  so  as  to  force  all  the  remaining  gas  into 
the  acid  flask.  The  tube  c  must  be  thoroughly  washed  out  into  the  flask 
with  distilled  water,  so  as  to  carry  down  the  acid  with  any  combined  gas 
which  may  have  reached  it ;  the  distilling  tube  must  also  be  washed  through 
into  the  acid  flask.  The  titration  then  proceeds  as  usual.  This  process  is 
particularly  serviceable  for  testing  commercial  animomacal  salts,  gas  liquor, 
etc.  (see  below).  The  results  are  extremely  accurate. 


2.    Indirect  Method. 

Ill  the  case  of  tolerably  pure  ammoniacal  salts  or  liquids,  free 
from  acid,  a  simple  indirect  method  can  be  used,  which  is  as 
follows : — 

If  the  ammoniacal  salt  be  boiled  in  an  open  vessel  with  normal  caustic 
alkali,  the  ammonia  is  entirely  set  free,  leaving  its  acid  combined  with  the 
fixed  alkali.  If,  therefore,  the  quantity  of  alkaline  solution  is  known,  the 
excess  beyond  that,  necessary  to  supplant  the  ammonia,  can  be  found  by  the 
ordinary  system  of  titration.  The  boiling  of  the  mixture  must  be  continued 
till  a  piece  of  red  litmus  paper,  held  in  the  steam  from  the  flask,  is  no  longer 
turned  blue. 

Example :  1'5  gm.  of  purest  sublimed  ammonic  chloride  was  placed  in  a 
wide-mouthed  flask  with  40  c.c.  of  normal  soda,  and  boiled  till  all  ammonia 
was  expelled,  then  titrated  back  with  normal  sulphuric  acid,  of  which 
11'9  c.c.  were  required;  2S'l  c.c.  of  normal  alkali  had  therefore  been 
neutralized,  which  multiplied  by  0'05337,  the  factor  for  ammonic  chloride, 
gave  T499  gm.,  instead  of  1'5  gm.  originally  taken. 


§    18.  GAS    LIQUOE.  71 

3.     Technical  Analysis  of  Gas  Liquor,   Sulphate  of  Ammonia,   Sal 
Ammoniac,  etc.,  arranged  for  the  use  of  Manufacturers. 

This  process  depends  upon  the  fact,  that  when  ammoniacal  salts 
are  heated  with  caustic  soda,  potash,  or  lime,  the  whole  of  the 
ammonia  is  expelled  in  a  free  state,  and  can  by  a  suitable  apparatus 
(fig.  24)  be  estimated  with  extreme  accuracy  (see  §  18.1). 

The  set  of  apparatus  here  described  consists  of  a  distilling  flask 
B,  and  condensing  flask  F,  fitted  together  in  such  a  manner,  that  no 
loss  of  free  ammonia  can  occur ;  the  whole  of  the  ammonia  being 
liberated  from  the  distilling  flask  into  a  measured  quantity  of  free 
acid  contained  in  the  condensing  flask,  where  its  amount  is  after- 
wards found  by  the  method  hereinafter  described. 

Analysis  of  Gas  Liquor. — This  liquid  consists  of  a  solution  of 
carbonates,  sulphates,  hyposulphites,  sulphides,  cyanides,  and  other 
salts  of  ammonia.  The  object  of  the  ammonia  manufacturer  is  to 
get  all  these  out  of  his  liquor  into  the  form  of  sulphate  or  chloride 
as  economically  as  possible.  The  whole  of  the  ammonia  existing 
as  free  or  carbonate  in  the  liquor,  can  be  distilled  off  at  a  steam 
heat;  the  fixed  salts,  however,  require  to  be  heated  with  soda, 
potash,  or  lime  (the  latter  is  generally  used  on  a  large  scale  as  most 
economical),  in  order  to  liberate  the  ammonia  contained  in  them. 

The  valuation  of  gas  liquor  is  almost  universally  made  in  Great 
Britain  by  Twaddle's  hydrometer,  every  degree  of  which  is  taken 
to  represent  what  is  technically  called  "two-ounce  strength;"  that  is 
to  say,  a  gallon  of  such  liquor  should  neutralize  exactly  two  ounces  by 
weight  of  concentrated  oil  of  vitriol — thus  5  degrees,  Twaddle,  is 
called  "  ten-ounce  "  liquor — but  experiment  has  clearly  proved,  that 
although  the  hydrometer  may  be  generally  a  very  convenient 
indicator  of  the  commercial  value  of  gas  liquor,  it  is  not  accurate 
enough  for  the  manufacturer  who  desires  to  work  with  the  utmost 
economy.  Sometimes  the  liquor  contains  a  good  deal  of  free 
ammonia,  and  in  such  case  the  hydrometer  would  show  it  to  be 
weaker  than  it  really  is ;  on  the  other  hand,  sometimes,  from 
accidental  causes,  other  solid  matters  than  ammonia  salts  occur  in 
the  liquor,  and  the  hydrometer  shows  it  to  be  stronger  than  it  really 
is.  The  method  of  saturation,  by  mixing  standard  acid  with  the 
liquor,  is  perhaps  more  correct  than  the  hydrometer;  but  this 
system  is  entirely  at  fault  in  the  presence  of  much  fixed  ammonia, 
and  is,  moreover,  a  very  offensive  and  poisonous  operation. 

The  apparatus  here  described  is  exactly  the  same  on  a  small 
scale  as  is  necessary  in  the  actual  manufacture  of  sulphate  of 
ammonia  in  quantities ;  and  its  use  enables  any  manufacturer  to 
tell  to  a  fraction  how  much  sulphate  of  ammonia  he  ought  to 
obtain  from  any  given  quantity  of  gas  liquor.  It  also  enables  him 
to  tell  exactly  how  much  ammonia  can  be  distilled  off"  with  heat 
alone,  and  how  much  exists  in  a  fixed  condition  requiring  lime. 

The  measures  used  in  this  process  are  on  the  metrical  system ; 


HH I I I I I h'"l""l 


u 
u 

0 


§    18.  GAS    LIQUOR.  73 

the  use  of  these  may,  perhaps,  at  first  sight  appear  strange  to 
English  manufacturers ;  but  as  the  only  object  of  the  process  is  to 
obtain  the  percentage  of  ammonia  in  any  given  substance,  it  is 
a  matter  of  no  importance  which  system  of  measures  or  weights  are 
used,  as  when  once  the  percentage  is  obtained,  the  tables  will  at 
once  show  the  result  in  English  terms  of  weight  or  measure. 

a  is  a  small  pipette,  holding  10  cubic  centimeters  to  the  mark  in  neck : 
this  is  the  invariable  quantity  of  liquor  used  for  the  analysis,  whatever  the 
strength  may  be.  This  measure  is  filled  to  the  mark  by  suction  and 
transferred,  without  spilling  a  drop,  to  flask  B— the  fittings  being  previously 
removed — the  tube  C  is  then  filled  in  the  same  manner,  with  strong 
caustic  soda  solution  from  a  clean  cup  or  other  vessel,  in  order  to  do 
which,  the  clip  at  the  top  must  be  opened ;  the  cork  is  then  replaced,  and 
the  flask  B  is  then  securely  imbedded  in  perfectly  dry  sand,  in  the  sand- 
bath  D.  The  graduated  pipette  E  is  then  filled  in  the  same  manner  to 
the  O  mark,  with  standard  acid,  and  20,  30,  40,  or  50  c.c.  (according 
to  the  estimated  strength  of  the  liquor)  allowed  to  flow  into  the  flask  F, 
through  the  cup  G,  which  is  filled  with  glass  wool  or  fibrous  asbestos.  The 
wool  should  be  completely  wetted  with  the  acid,  so  that  any  vapours  of 
ammonia  which  may  escape  the  acid  in  the  flask  shall  become  absorbed 
by  the  acid.  The  quantity  of  standard  acid  to  be  used  is  regulated  by  the 
approximately  known  strength  of  the  liquor,  which  of  course  can  be  told  by 
Twaddle's  hydrometer:  thus,  for  a  liquor  of  3°  Twaddle=6-oz.  liquor, 
20  c.c. — 8-oz ,  25  c.c. — 10-oz.,  30  c.c.  of  acid  will  be  sufficient — but  there 
must  always  be  an  excess.  The  required  quantity  cm  always  be  approx- 
imately known,  since  every  10  c.c.  of  acid  represents  1  per  cent,  of  ammonia. 
The  standard  acid  having  been  carefully  measured  through  the  glass  wool, 
the  apparatus  is  fitted  together  at  H  by  the  elastic  tube,  and  the  india-rubber 
stoppers  securely  inserted  in  both  flasks;  this  being  done,  the  lamp  is 
lighted  under  the  sand-bath,  and  at  the  same  time  the  spring-clip  on  C  is 
pressed,  so  as  to  allow  about  two-thirds  of  the  caustic  soda  to  flow  into  B ; 
the  rest  will  gradually  empty  itself  during  the  boiling.  The  heat  is  continued 
to  boiling,  and  allowed  to  go  on  till  the  greater  bulk  of  the  liquid  in  B 
is  boiled  away  into  F.  A  quarter  of  an  hour  is  generally  sufficient' for  this 
purpose,  but  if  the  boiling  is  continued  till  the  liquid  in  B  just  covers  the 
bottom  of  the  flask,  all  the  ammonia  will  have  gone  over  to  F;  during 
the  whole  operation  the  distilling  tube  must  never  dip  into  the  acid  in  F. 
In  order  to  get  rid  of  the  last  traces  of  ammonia  vapour  out  of  B,  the  lamp 
is  removed,  and  the  mouth  being  applied  to  the  tube  over  the  spring  clip, 
the  latter  is  opened,  and  a  good  blast  of  air  immediately  blown  through. 
The  apparatus  may  then  be  detached  at  H ;  distilled  or  good  boiled  drink- 
ing water  is  then  poured  repeatedly  through  G  in  small  quantities,  till 
all  traces  of  acid  are  removed;  and  some  water  is  also  poured  down  the 
distilling  tube,  so  as  to  wash  all  traces  of  ammonia  which  may  be  hanging 
about  into  flask  F.  This  latter  now  contains  all  the  ammonia  out  of  the 
sample  of  liquor,  with  an  excess  of  acid,  and  it  is  necessary  now  to  find  out 
the  quantity  of  acid  in  excess.  This  is  done  by  means  of  the  burette  I,  and 
the  standard  solution  of  soda,  which  soda  is  of  exactly  the  same  strength  as 
the  standard  acid.  In  order  to  find  out  how  much  of  the  standard  acid  has  been 
neutralized  by  the  ammonia  in  the  liquor  distilled,  the  burette  I  is  filled  to  O 
with  standard  soda,  and  one  drop  of  methyl  orange,  or  a  sufficiency  of  any 
other  indicator,  other  than  phenolphthalein,  being  added  to  the  cooled  contents 
of  flask  F,  the  soda  is  slowly  dropped  into  it  from  the  burette,  with  constant 
shaking,  until  the  indicator  changes  colour.  The  number  of  c.c.  of  soda  so 
used,  deducted  from  th3  number  of  c.c.  of  standard  acid  used,  will  show 
the  number  neutralized  by  the  ammonia  in  the  liquor  distilled ;  therefore,  if 


74  VOLUMETRIC   ANALYSIS.  §    18. 

the  number  of  c.c.  of  soda  used  to  destroy  the  pink  colour  be  deducted 
from  the  number  of  c.c.  of  standard  acid  originally  used,  it  will  show  the 
number  of  c.c.  of  standard  acid  neutralized  by  the  ammonia,  which  has  been 
distilled  out  of  the  liquor,  and  the  strength  of  the  solutions  is  so  arranged 
that  this  is  shown  without  any  calculation.  The  following  examples  will 
suffice  to  show  this :— Suppose  that  a  liquor  is  to  be  examined  which  marks 
5°  Twaddle,  equal  to  10-ounce  liquor;  10  c.c.  of  it  is  distilled  into  30  c.c. 
of  the  standard  acid,  and  it  has  afterwards  required  C  c.c.  of  standard 
soda  to  neutralize  it;  this  leaves  24  c.c.  as  the  volume  of  acid  saturated 
by  the  distilled  ammonia,  and  this  represents  2'4  per  cent. ;  and  on  referring 
to  the  table  it  is  found  that  this  number  corresponds  to  a  trifle  more  than 
11  ounces,  the  actual  figures  being  2*384  per  cent,  for  11-ounce  strength. 

The  strength  of  the  standard  soda*  and  acid  solutions  is  so 
arranged,  that  when  10  c.c.  of  liquor  is  distilled,  every  10  c.c.  of 
acid  solution  represents  1  per  cent,  of  ammonia  in  the  liquor.  In 
like  manner  13  c.c.  of  acid  will  represent  1*3  per  cent,  of  ammonia 
corresponding  to  6-ounce  liquor. 

The  burette  is  divided  into  tenths  of  a  cubic  centimeter,  and 
those  who  are  familiar  with  decimal  calculations  can  work  out  the 
results  to  the  utmost  point  of  accuracy ;  the  calculation  being,  that 
every  1  per  cent,  of  ammonia  requires  4 '61  ounces  of  concentrated 
oil  of  vitriol  (sp.  gr.  1  '845)  per  gallon,  to  convert  it  into  sulphate  : 
thus,  suppose  that  10  c.c.  of  any  given  liquor  have  been  distilled, 
and  the  quantity  of  acid  required  amounts  to  18-6  c.c.,  this  is 
1*86  per  cent.,  and  the  ounce  strength  is  shown  in  ounces  and 
decimal  parts  as  follows  : — 

4-61 
1-86 


2766 
3688 
461 

8.5746  ounces  of  oil  of  vitriol. 


The  liquor  is  therefore  a  trifle  over  8J-ounce  strength. 

Spent  Liquors. — It  is  frequently  necessary  to  ascertain  the 
percentage  of  ammonia  in  spent  liquors,  to  see  if  the  workman 
have  extracted  all  the  available  ammonia.  In  this  case  the  same 
measure,  10  c.c.  of  the  spent  liquor,  is  taken,  and  the  operation 
conducted  precisely  as  in  the  case  of  a  gas  liquor. 

Example  :  10  c.c.  of  a  spent  liquor  were  distilled,  and  found  to  neutralize 
3  c.c.  of  acid ;  this  represents  three-tenths  of  a  per-ceut.  equal  to  1-oz.  and 
four-tenths  of  an  ounce,  or  nearly  1|  oz.  Such  a  liquor  is  too  valuble  to 
throw  away,  and  should  be  worked  longer  to  extract  more  ammonia. 

*  Soda  is  recommended  in  preference  to  ammonia  for  the  standard  alkali,  as  it  was 
found  that  a  solution  of  ammonia  containing  *01  gin.  per  c.c.  readily  lost  strength  by 
keeping. 


§ 


GAS    LIQUOR. 


75 


Analysis  of  Sulphate  of  Ammonia,  or  Sal  Ammoniac :  An  average 
sample  of  the  salt  being  drawn,  ten  grams  are  weighed,  transferred  without 
loss  to  a  beaker  or  flask  having  a  100  c.c.  mark  upon  it,  distilled  or  boiled 
drinking  water  poured  on  it,  and  well  stirred  till  dissolved,  and  finally 
water  added  exactly  to  the  mark.  The  10  c.c.  measure  is  then  filled  with 
the  solution,  and  emptied  into  the  distilling  flask  B;  30  c.c.  of  standard 
acid  are  put  into  flask  F  and  the  distillation  carried  on  precisely  as  in 
the  case  of  a  gas  liquor.  The  number  of  c.c.  of  standard  acid  required 
shows  directly  the  percentage  of  ammonia;  thus,  if  24*6  c.c.  are  used  in 
the  case  of  sulphate,  it  contains  24' 6  per  cent,  of  ammonia. 

The  liquors  when  tested  must  be  measured  at  ordinary  tempera- 
tures, say  as  near  to  60°  F.  as  possible.  The  standard  solutions 
must  be  kept  closely  stoppered  and  in  a  cool  place. 

The  following  table  is  given  to  avoid  calculations ;  of  course,  it 
will  be  understood  that  the  figures  given  are  on  the  assumption 
that  the  whole  of  the  ammonia  contained  in  the  liquor  is  extracted 
in  the  manufacture  as  closely  as  it  is  in  the  experiment.  With  the 
most  perfect  arrangement  of  plant,  however,  this  does  not  as  a  rule 
take  place ;  but  it  ought  .to  be  very  near  the  mark  with  proper 
apparatus,  and  care  on  the  part  of  workmen. 


Approxi- 

Acid  in  c  c.         NH' 
and  tenths. 

Ounce 
strength 
per 
gallon. 

Weight  of  Sulphuric  Acid  in  pounds 
and  decimal  parts  required  for  each 
gallon  of  liquor. 

Yield  of 
Sulphate 
per  gallon  in 
Ibs.  and 
decimal 
parts. 

C.  O.  V. 

169°  Tw. 

B.  O.  V. 
144°  Tw. 

Chamber 
Acid 
120°  Tw. 

2-2             '2168 

1 

•0625 

•0781 

•0893 

•0841 

4-3 

•4336 

2 

•1250 

•1562 

•1786 

•1682 

6'5 

•6504 

3 

•1875 

•2343 

•2679 

•2523 

87 

•8672 

4 

•2500 

•3124 

•3572 

•3364 

lO'l           1-0840 

5 

•3125 

•3905 

•4465 

•4205 

13'0 

1-3000 

6 

•3750 

•4686 

•5358 

•5046 

15-2 

1-5176 

7 

•4375 

•5467 

•6251 

•5887 

17'3           1-7344 

8 

•5000 

•6248 

•7144 

•6728 

19-5           1-9512 

9 

•5625 

•7029 

•8037 

•7569 

21-7 

2-1680 

10 

•6250 

•7810 

•8930 

•8410 

23-8 

2-3840 

11 

•6875 

•8591 

•9823 

•9251 

26-0      I     2-6016 

12 

•7500 

•9372 

1-0716 

1-0092 

28-2 

2-8184 

13 

•8125 

1-0153 

1-1609 

1-0933 

30-4 

30350 

14 

•8750 

1-0934 

1-2502 

1-1774 

32-5 

3-2520 

15 

•9375 

1-1715 

1-3395 

1-2615 

34-7 

3-4688 

16 

1-0000 

1-2496 

1-4288 

1-3456 

36-9 

3-6856 

17 

1-0625 

1-3277 

1-5181 

1-4297 

39-0 

3-9024 

18 

1-1250 

1-4058 

1-6074 

1-5138 

41-2 

4-1192 

19 

1-1875 

1-4839 

1-6967 

1-5979 

43-3 

4-3360 

20 

1-2500 

1-5620 

1-7860 

1-6820 

The  weight  of  sulphuric  acid  being  given  in  decimals  renders  it 
very  easy  to  arrive  at  the  weight  necessary  for  every  thousand 
gallons  of  liquor,  by  simply  moving  the  decimal  point ;  thus  8-oz. 
liquor  would  require  500  Ibs.  of  concentrated  oil  of  vitriol,  625  Ibs. 


76  VOLUMETRIC  ANALYSIS.  §    18. 

of  brown  oil  of  vitriol,  or  71 4  J  Ibs.  chamber  acid  for  every  1000 
gallons,  and  should  yield  in  all  cases  672*8  (say  673)  Ibs.  of 
sulphate. 

4.    Combined  Nitrogen  in  Organic  Substances. 

This  process  consists  in  heating  the  dried  substance  in  a 
combustion  tube  with  soda  lime,  by  which  the  nitrogen  is  con- 
verted into  ammonia;  and  this  latter  being  led  into  a  measured 
volume  of  normal  acid  contained  in  a  suitable  bulb  apparatus, 
combines  with  its  equivalent  quantity ;  the  solution  is  then 
titrated  residually  with  standard  alkali  for  the  excess  of  acid, 
and  thus  the  quantity  of  ammonia  found. 

As  the  combustion  tube  Avith  its  arrangements  for  organic 
analysis  is  well  known,  and  described  in  any  of  the  standard  books 
on  general  analysis,  it  is  not  necessary  to  give  a  description  here. 

Instead  of  leading  the  ammonia  through  normal  acid,  hydro- 
chloric acid  of  unknown  strength  may  be  used,  the  liquid  brought 
into  the  distilling  apparatus,  and  the  ammonic  chloride  estimated 
by  the  process  described  in  §  18.1. 

When  it  is  necessary  to  estimate  very  minute  portions  of 
ammonia,  it  may  be  brought  into  the  form  of  chloride,  and 
estimated  by  decinormal  silver  solution  (§  38) ;  or  in  many  cases 
preferably  by  Nessler's  test,  described  in  the  section  on  Water 
Analysis. 

5.     Kjeldahl's    Method. 

This  has  met  with  considerable  acceptance  in  lieu  of  the 
combustion  method,  on  account  of  its  easy  management  and 
accurate  results.  Moreover,  unlike  the  combustion  method,  the 
ammonia  .is  obtained  free  from  organic  matters  or  colour.  It  was 
first  described  by  the  author  (Z.  a.  C.  xxii.  366),  and  has  since 
been  commented  upon  by  many  operators,  among  whom  are 
Warington  (C.  N.  lii.  162),  Pfeiffer  and  Lehmann  (Z.  a.  C. 
xxiv.  388),  Marcker  and  others  (Z.  a.  C.  xxiii.  553;  xxiv.  199, 
393;  xxv.  149,  155;  xxvi.  92;  xxvii.  222,  398). 

The  process  consists  in  heating  the  organic  substance  in  a  flask, 
with  concentrated  sulphuric  acid,  to  its  boiling  point,  and  when 
the  oxidation  is  nearly  completed,  adding  finely  powdered  per- 
manganate of  potash  in  small  quantities  till  a  green  or  pink  colour 
remains  constant :  the  whole  of  the  nitrogen  is  thus  converted  into 
ammonic  sulphate.  The  flask  is  then  cooled,  diluted  with  water 
somewhat,  excess  of  caustic  soda  added,  the  ammonia  distilled  off 
into  standard  acid,  and  the  amount  found  by  titration  in  the  usual 
way. 

Some  practical  difficulties  occur  in  the  process  :  for  instance,  the 
final  distillation  with  concentrated  alkali  gives  rise  to  bumping, 
with  a  tendency  to  spray  the  liquid  into  the  tube  which  leads  into 


§18.  COMBINED    NITROGEN.  77 

the  acid.  To  overcome  this,  it  is  necessary  to  put  two  or  three 
pieces  of  metallic  zinc  into  the  flask,  which,  by  the  generation  of 
hydrogen  gas,  facilitate  the  operation.  Experience  has  however 
shown  that  though  this  is  the  case,  there  is  a  greater  chance  of 
the  distillate  being  contaminated  with  traces  of  alkali.  This  is 
especially  so  if  a  large  excess  of  alkali  with  much  zinc  is  used. 
Therefore  it  is  proper  to  use  only  a  moderate  excess  of  alkali,  'and 
not  much  zinc. 

Another  difficulty  is,  that  if  nitrates  are  present  in  the  compound 
analyzed,  their  reduction  to  ammonia  is  not  certain  nor  regular, 
and  unless  this  difficulty  be  overcome  the  value  of  the  process  is 
limited. 

Warington  has  investigated  this  contingency,  and  finds  that  in 
order  to  get  rid  of  them  before  the  treatment  with  sulphuric  acid, 
the  material  is  best  digested  with  ferrous  sulphate  and  strong 
hydrochloric  acid  with  heat,  finally  carried  to  dryness  •  the  sulphuric 
acid  is  then  added,  and  the  process  carried  out  as  recommended 
by  Kjeldalil.  When  this  method  is  adopted  the  nitrates  are 
separately  estimated  by  some  other  method.  In  the  modified 
method  given  below,  the  ISr  existing  as  nitrate  is  converted  into- 
]STH3,  so  that  one  operation  estimates  tiae_  whole  of  the  nitrogen 
as  ammonia. 

The  experience  of  many  hundreds  of  operators  since  this 
method  was  first  introduced  has  resulted  in  rendering  it  as  perfect 
as  need  be,  and  no  better  arrangement  of  the  process  can  be  given 
than  that  adopted  by  the  U.  S.  Association  of  Official  Agricultural 
Chemists  (1887 — 8).  This  arrangement  in  all  essential  particulars 
will  now  be  described,  omitting  the  details  as  to  some  of  the  special 
forms  of  apparatus,  and  which  are  not  absolutely  essential.  The 
method  requires  the  following  articles  : — 

1 .  Standard  acid,  which  may  be  either  sulphuric  or  hydrochloric ; 
a  convenient  strength  is  semi-normal. 

2.  Standard  alkali,  either  ammonia,  soda,  or  potash,  of  corres- 
ponding strength  to  the  acid. 

3.  Concentrated  sulphuric  acid  free  from  nitrates  and  ammonic 
sulphate.* 

4.  Mercuric    oxide    prepared    in    the   wet   way   or    metallic 
mercury. 

5.  Powdered  potassic  permanganate. 

6.  Granulated  zinc. 

*  Commercial  oil  of  vitriol  frequently  contains  ammonia,  owing  to  the  fact  that 
makers  sometimes  add  ammonic  sulphate  during  concentration  in  order  to  get  rid  of 
nitrous  compounds.  Meldola  and  Moritz  state  that  any  traces  of  ammonia  may  be 
destroyed  by  digesting  the  acid  for  two  or  three  hours  at  a  temperature  below  boiling, 
with  sodic  or  potassic  nitrite,  in  the  proportion  of  0'5  gm.  of  the  salt  to  100  c.c.  of 
acid.  Lunge  objected  to  this  treatment,  because  of  the  probable  formation  of  nitro- 
sulphuric  acid.  Experiments  have  since  been  made  by  Moritz  which  prove  that  the 
objection  is  groundless,  provided  the  digestion  is  carried  on  for  a  period  sufficient  to 
expel  the  nitrous  acid  (J.  S.  C.  I.  ix.  443).  The  purification  of  the  acid  may  of  course 
be  obviated  by  ascertaining  once  for  all  the  amount  of  ammonia  in  any  given  stock  of 
acid,  by  making  a  blank  experiment  with  pure  sugar  and  allowing  in  all  cases  for  the 
amount  of  .N  H;i  so  found. 


78  VOLUMETRIC  ANALYSIS.  §    18. 

7.  Solution  of  potassic  sulphide  in  water,  40  gm.  in  the  liter. 

8.  A  saturated  solution  of  caustic  soda  free    from  nitrates  or 
nitrites. 

9.  A  suitable  indicator — cochineal   is  recommended,  but  any 
other  except  phenolphthalein  may  be  used. 

10.  Digestion  flasks   with   long    neck,    holding   about    200 — • 
250  c.c.     These  flasks  should  be  well  annealed  and  not  too  thick — 
the  neck  about  f  inch  wide,  and  3J — 4  inches  long. 

11.  Distillation  flasks  of  hard  Bohemian  glass,  550 — 600  c.c. 
capacity,  fitted  with  a  rubber  stopper  and  a  bulb  tube  above  to 
prevent  the  spray  of  the  boiling  alkaline  liquid  from  being  carried 
over  into  the  condenser.     I  invariably  use  a  tube  of  f  in.  bore, 
with  two  bulbs    1  in.  diameter  just  above  the  stopper,  and  have 
proved  the  absolute  security  of  this  tube  in  preventing  the  passage 
of  any  trace  of  alkali  into  the  distillate. 

12.  The   condenser.     Owing   to   the   undoubted   solubility  of 
glass  in  fresh  distilled  water  containing  ammonia,  it  is  advisable  to 
have  the  condenser  tube  made  of  block  tin.     This  should  be  about 
half-an-inch  wide  externally,  and  is  connected  with  the  bulb  tube 
of  the  distilling  flask  with  stout  pure  rubber  tube.     It  is  surrounded 
by  either  a  metal  or  glass  casing,  through  which  cold  water  is 
passing  in  the  usual  manner.     It  is  very  easy  to  fit  up  such  an 
arrangement  with  the  condenser  tubes  made  entirely  of  glass  sold 
by  the  dealers  in  chemical  apparatus.     The  end  of  the  condenser 
tube  may  be  simply  inserted  into  the  neck  of  a  flask  containing 
the  standard  acid,  or  it  may  have  a  delivery  tube  connected  by 
rubber  leading  into  a  beaker.     There  is  no  necessity  in  any  case 
for  dipping  the  delivery  tube  into  the  acid. 

The  condenser  recommended  by  the  Association,  when  a  number 
of  estimations  are  carried  on  at  the  same  time,  was  devised  by 
Professor  Johnson,  and  consists  of  a  copper  tank  supported  by 
a  wooden  frame,  so  that  its  bottom  is  1 1  inches  above  the  work- 
bench on  which  it  stands.  This  tank  is  16  inches  high,  32  inches 
long,  and  3  inches  wide  from  front  to  back,  widening  above  to 
6  inches.  It  is  provided  with  a  water-supply  tube  which  goes  to 
the  bottom  and  a  larger  overflow  pipe  above.  The  block  tin 
condensing  tubes,  whose  external  diameter  is  f  of  an  inch,  seven 
in  number,  enter  the  tank  through  holes  in  the  front  side  of  it 
near  the  top,  above  the  level  of  the  overflow,  and  pass  down 
perpendicularly  through  the  tank  and  out  through  rubber  stoppers 
tightly  fitted  into  holes  in  the  bottom.  They  project  about 
1J  inches  below  the  bottom  of  the  tank,  and  are  connected  by 
short  rubber  tubes  with  glass  bulb  tubes  of  the  usual  shape,  which 
dip  into  glass  precipitating  beakers.  These  beakers  are  6|  inches 
high,  3  inches  in  diameter  below,  somewhat  narrower  above,  and 
of  about  500  c.c.  capacity.  The  titration  can  be  made  directly  in 
them.  The  seven  distillation  flasks  are  supported  on  a  sheet-iron 
shelf  attached  to  the  wooden  frame  that  supports  the  tank  in  front 


§    18.  COMBINED    NITROGEN.  79 

of  the  latter.  Where  each  flask  is  to  stand  a  circular  hole  is  cut, 
with  three  projecting  lips,  which  support  the  wire  gauze  under  the 
flask,  and  three  other  lips  which  hold  the  flask  in  place  and 
prevent  its  moving  laterally  out  of  place  while  distillation  is  going 
on.  Below  this  sheet-iron  shelf  is  a  metal  tube  carrying  seven 
Bunsen  burners,  each  with  a  stop-cock  like  those  of  a  gas 
combustion  furnace.  These  burners  are  of  larger  diameter  at  the 
top,  which  prevents  smoking  when  covered  with  fine  gauze  to 
prevent  the  flame  from  striking  back. 

13.  The  stand  for  holding  the  digestion  flasks  consists  of 
a  pan  of  sheet-iron,  29  inches  long  by  8  inches  wide,  on  the  front 
of  which  is  fastened  a  shelf  of  sheet-iron  as  long  as  the  pan, 
5  inches  wide  and  4  inches  high.  In  this  are  cut  six  holes 
If  inches  in  diameter.  At  the  back  of  the  pan  is  a  stout  wire 
running  lengthwise  of  the  stand,  8  inches  high,  with  a  bend  or 
depression  opposite  each  hole  in  the  shelf.  The  digestion  flask 
rests  with  its  lower  part  over  a  hole  in  the  shelf  and  its  neck  in 
one  of  the  depressions  in  the  wire  frame,  which  holds  it  securely 
in  position.  Heat  is  supplied  by  low  Bunsen  burners  below  the 
shelf.  With  a  little  care  the  naked  flame  can  be  applied  directly 
to  the  flask  without  danger. 

Analysis :  Prom  0'7  to  1  gm.  of  the  substance  to  be  analysed  is  brought  into 
a  digestion  flask  with  approximately  0'7  gm.  of  mercuric  oxide  or  0'5  gm. 
metal  and  20  c.c.  of  sulphuric  acid.*  The  flask  is  placed  on  wire  gauze  over 
a  small  Bunsen  burner  in  an  upright  position,  or  the  frame  above  described  in 
an  inclined  position,  and  heated  below  the  boiling-point  of  the  acid  for  from 
five  to  fifteen  minutes,  or  until  frothing  has  ceased.  The  heat  is  then  raised 
till  the  acid  boils  briskly.  No  further  attention  is  required  till  the  contents 
of  the  flask  have  become  a  clear  liquid,  which  is  colourless,  or  at  least  has 
only  a  very  pale  straw  colour.  The  flask  is  then  removed  from  the  frame, 
held  upright,  and,  while  still  hot,  permanganate  is  dusted  in  carefully,  and 
in  small  quantity  at  a  time,  till  after  shaking  the  liquid  remains  of  a  green 
or  purple  colour.  After  cooling,  the  contents  of  the  flask  are  transferred  to 
the  distilling  flask  with  water,  and  to  this  25  c.c.  of  potassic  sulphide 
solution  are  added,  50  c.c.  of  the  soda  solution,  or  sufficient  to  make  the 
reaction  strongly  alkaline,  and  a  few  pieces  of  granulated  zinc.  The  flask  is 
at  once  connected  with  the  condenser,  and  the  contents  of  the  flask  are  distilled 
till  all  ammonia  has  passed  over  into  the  standard  acid  contained  in  the 
precipitating  flask  previously  described,  and  the  concentrated  solution  can 
no  longer  be  safely  boiled.  This  operation  usually  requires  from  twenty  to 
forty  minutes.  The  distillate  is  then  titrated  with  standard  alkali. 

The  use  of  mercury  or  its  oxide  in  this  operation  greatly  shortens  the  time 
necessary  for  digestion,  which  is  rarely  over  an  hour  and  a  half  in  the  case 
of  substances  most  difficult  to  oxidize,  and  is  more  commonly  less  than  an 
hour.  In  most  cases  the  use  of  permanganate  is  quite  unnecessary,  but  it  is 
believed  that  in  exceptional  cases  it  is  required  for  complete  oxidation,  and 
in  view  of  the  uncertainty  it  is  always  used.  Potassic  sulphide  removes  all 
mercury  from  solution,  and  so  prevents  the  formation  of  mercuro-ammonium 

*  Some  albuminoid  substances,  such  as  pure  isinglass,  refuse  apparently  to  yield  the 
theoretical  proportion  of  ammonia  by  treatment  with  ordinary  sulphuric  acid  (see 
Oddy  and  Cohen,  J".  S.  C.  I.  ix.  17).  This  may  arise  from  insufficient  heating  or 
from  weakness  in  the  acid ;  under  such  circumstances  I  am  inclined  to  think  that  the 
addition  of  some  Nordhausen  acid  to  increase  the  strength  or  some  potassic  sulphate 
to  increase  the  boiling  point  of  the  acid  would  insure  a  more  perfect  decomposition. 


80  VOLUMETRIC   ANALYSIS.  §    ]  9. 

compounds  which  are  not  completely  decomposed  by  soda  solution.  The 
addition  of  zinc  gives  rise  to  an  evolution  of  hydrogen,  and  prevents  violent 
bumping.  Previous  to  use  the  reagents  should  be  tested  by  a  blank 
experiment  with  sugar,  which  will  partially  reduce  any  nitrates  that  are 
present  which  might  otherwise  escape  notice. 

The  following  modification  must  be  used  for  the  determination 
of  nitrogen  in  substances  which  contain  nitrates  when  it  is  desired 
to  use  this  method. 

Estimation  of  Nitrogen,  including-  the  Nitrogen  of  Nitrates,  by  a 
Modified  Method  of  Kjeldahl.— Bring  from  07  to  T4  gm.  of  the 
substance  to  be  analyzed  into  a  Kjeldahl  digesting  flask,  add  to  this  36  c.c. 
of  sulphuric  acid  containing  2  gm.  of  salicylic  acid,  and  shake  thoroughly. 
Then  add  gradually  3  gm.  of  zinc-dust,  shaking  the  contents  of  the  flask  at 
the  same  time.  Finally,  add  two  or  three  drops  of  platinic  chloride  solution, 
and  place  the  flask  on  the  stand  for  holding  the  digestion  flasks,  where  it 
is  heated  over  a  low  flame  until  all  danger  from  frothing  has  passed.  The 
heat  is  then  raised  until  the  acid  boils  briskly,  and  the  boiling  continued 
until  white  fumes  no  longer  pour  out  of  the  flask.  This  requires  about  five 
or  ten  minutes.  Add  now  about  0  7  gm.  mercuric  oxide,  and  continue  the 
boiling  until  the  liquid  in  the  flask  is  colourless  or  nearly  so.  (In  case  the 
contents  of  the  flask  are  likely  to  become  solid  before  this  point  is  reached 
add  10  c.c.  more  of  sulphuric  acid.)  Complete  the  oxidation  with  a  little 
permanganate  in  the  usual  way,  and  proceed  with  the  distillation  as  described 
above. 

The  titration  of  the  distillate  is  made  in  the  usual  way  with 
methyl  orange  or  some  other  indicator  other  than  phenolphthalein. 
Kjeldahl  prefers  to  titrate  a  measured  small  portion  of  the 
distillate  for  excess  of  acid  by  the  iodine  and  starch  reaction 
described  in  §  19. 

The  substances  available  for  the  accurate  estimation  of  their 
nitrogen  by  the  Kjeldahl  method  are:  —  All  amides  and 
ammonium  bases,  the  pyridine  and  chinolin  bodies,  the  alkaloids, 
the  bitter  principles,  the  albumenoids  and  kindred  substances. 
All  nitro,  nitroso,  azo,  diazo,  hydrazo,  and  amido-azo  compounds 
with  the  compounds  of  nitric  and  nitrous  acid,  however,  require 
previous  treatment  similar  to  that  suggested  by  War  ing  ton,  or 
must  be  dealt  with  by  the  modified  process  above  described. 


ACIDIMETRY    OB    THE    TITRATION    OF    ACIDS. 

§  19.  THIS  operation  is  simply  the  reverse  of  all  that  has  been 
said  of  alkalies,  and  depends  upon  the  same  principles  as  have 
been  explained  in  alkalimetry. 

With  free  liquid  acids,  such  as  hydrochloric,  sulphuric,  or  nitric, 
the  strength  is  generally  taken  by  means  of  the  hydrometer  or 
specific-gravity  bottle,  and  the  amount  of  real  acid  in  the  sample 
ascertained  by  reference  to  the  tables  constructed  by  Otto, 
Bineau,  or  Ure.  The  specific  gravity  may  very  easily  be  taken 
with  the  pipette,  as  recommended  with  ammonia,  and  of  course  the 


§    19.  ACIDIMETRY.  81 

real  acid  may  be  quickly  estimated  by  normal  caustic  alkali  and  an 
appropriate  indicator. 

In  the  case  of  titrating  concentrated  acids  of  any  kind  it  is 
preferable  in  all  cases  to  weigh  accurately  a  small  quantity,  dilute 
to  a  definite  volume,  and  take  an  aliquot  portion  for  the  analysis. 

Delicate   End-reaction   in   Acidimetry. 

If  an  alkaline  iodate  or  bromate  be  added  to  a  solution  of  an 
alkaline  iodide  in  the  presence  of  a  mineral  acid,  iodine  is  set  free 
and  remains  dissolved  in  the  excess  of  alkaline  iodide,  giving  the 
solution  the  well-known  colour  of  iodine.  This  reaction  has  been 
long  observed,  and  is  capable  of  being  used  with  excellent  effect  as 
an  indicator  for  the  delicate  titration  of  acids,  and  therefore  of 
alkalies,  by  the  residual  method.  Kjeldahl,  for  instance,  uses  it 
in  his  ammonia  process,  where  the  distillate  contains  necessarily  an 
excess  of  standard  acid.  The  reaction  is  definite  in  character,  and 
may  be  used  in  various  ways  in  volumetric  processes.  For  instance, 
potassic  bromate  liberates  iodine  in  exact  proportion  to  its  contained 
oxygen  in  the  presence  of  excess  of  dilute  mineral  acid,  and  the 
iodine  so  liberated  may  be  accurately  titrated  with  sodic  thiosulphate. 
In  acidimetry,  however,  the  method  is  simply  used  for  its  exceeding 
delicacy  as  an  end-reaction,  one  drop  of  T^Q-  sulphuric,  nitric,  or 
hydrochloric  acid  being  quite  sufficient  to  cause  a  deep  blue  colour 
in  the  presence  of  starch. 

The  adjustment  of  the  standard  liquids  is  made  as  follows : — 
2  or  3  c.c.  of  y^-  acid  is  run  into  a  flask,  diluted  somewhat  with 
water,  and  a  crystal  or  two  of  potassic  iodide  thrown  in ;  1  or  2  c.c. 
of  a  5  per  cent,  solution  of  potassic  iodate  are  then  added,  which 
at  once  produces  a  brown  colour,  due  to  free  iodine.  A  solution 
of  sodic  thiosulphate  is  added  from  a  burette,  with  constant 
shaking,  until  the  colour  is  nearly  discharged ;  a  few  drops  of 
freshly  prepared  starch  indicator  are  now  poured  in,  and  the  blue 
colour  removed  by  the  very  cautious  addition  of  thiosulphate. 
The  quantity  of  thiosulphate  used  represents  the  comparative 
strengths  of  it  and  the  standard  acid,  and  is  used  as  the  basis 
of  calculation  in  other  titrations.  The  first  discharge  of  the  blue 
colour  must  be  taken  in  all  cases  as  the  correct  ending,  because  on 
standing  a  few  minutes  the  blue  colour  re-occurs,  due  to  some 
obscure  reaction  from  the  thiosulphate.  This  has  been  probably 
regarded  as  one  of  the  drawbacks  of  the  process,  and  another  is  the 
instability  of  the  thiosulphate  solution ;  but  these  by  no  means 
invalidate  its  accuracy,  and  it  moreover  possesses  the  advantage  of 
being  applicable  to  excessively  dilute  solutions,  and  may  be  used 
by  artificial  light.  The  organic  acids  cannot  be  estimated  by  this 
method,  the  action  not  being  regular.  Neutral  alkaline  and  alkaline 
earthy  salts  have  no  interference,  but  salts  of  the  organic  acids  and 
borates  must  be  absent. 


82  VOLUMETRIC  ANALYSIS.  §    20. 

ACETIC    ACID. 


§  20.  IN  consequence  of  the  anomaly  existing  between  the  sp.  gr. 
of  strong  acetic  acid  and  its  actual  strength,  the  hydrometer  is  not 
reliable,  but  the  volumetric  estimation  is  now  rendered  extremely 
accurate  by  using  phenolphthalein  as  indicator,  acetates  of  the 
alkalies  and  alkaline  earths  having  a  perfectly  neutral  behaviour  to 
this  indicator.  Even  coloured  vinegars  may  be  titrated  when 
highly  diluted.  Where,  however,  the  colour  is  too  much  for  this 
method  to  succeed,  recourse  must  be  had  to  litmus  paper,  upon 
which  streaks  of  the  liquid  should  be  made  from  time  to  time 
during  the  titration  with  a  glass  rod. 

Several  processes  have  at  various  times  been  suggested  for  the 
accurate  and  ready  estimation  of  acetic  acid,  among  which  is  that 
of  Greville  Williams,  by  means  of  a  standard  solution  of  lime 
syrup.  The  results  obtained  were  very  satisfactory. 

C.  Mohr's  process  consists  in  adding  to  a  known  quantity  of 
the  acid  a  known  excessive  quantity  of  baric  or  calcic  carbonate  in 
fine  powder.  Pure  calcic  carbonate  is  preferable,  as  it  dissolves 
more  readily  than  baric  salt.  When  the  decomposition  is  as  nearly 
as  possible  complete  in  the  cold,  the  mixture  must  be  heated  to 
expel  the  CO2,  and  to  complete  the  saturation;  the  residual 
carbonate  is  then  brought  upon  a  filter,  washed  with  boiling  water, 
and  titrated  with  excess  of  normal  acid  and  back  with  alkali. 

This  process  is  applicable  in  all  cases,  and  however  dark  the 
colour  may  be.  In  testing  the  impure  brown  pyroligneous  acid  it 
is  especially  serviceable. 

Pettenkofer  titrates  acetic  acid  or  vinegar  with  a  known 
excess  of  baryta  water;  and  estimates  the  excess  of  the  latter 
with  ~-fj  nitric  or  oxalic  acid  by  the  help  of  turmeric  paper. 

The  titration  of  acetic  acid  or  vinegar  may  also  be  performed  by 
the  ammonio-cupric  solution  described  in  §  14.10. 

1.  Free  Mineral  Acids  in  Vineg-ar. — Hehner  has  devised  an 
excellent  method  for  this  purpose  (Analyst  i.  105). 

Acetates  of  the  alkalies  are  always  present  in  commercial  vinegar; 
and  when  such  vinegar  is  evaporated  to  dryness,  and  the  ash  ignited, 
the  alkalies  are  converted  into  carbonates  having  a  distinct  alkaline 
reaction  on  litmus;  if,  however,  the  ash  has  a  neutral  or  acid 
reaction,  some  free  mineral  acid  must  have  been  present.  The 
alkalinity  of  the  ash  is  diminished  in  exact  proportion  to  the 
amount  of  mineral  acid  added  to  the  vinegar  as  an  adulteration. 
Hence  the  following  process  : — 

50  c.c.  of  the  vinegar  are  mixed  with  25  c.c.  of  ^  soda  or  potash,  evaporated 
to  dryness,  and  ignited  at  a  low  red  heat  to  convert  the  acetates  into  carbonates ; 
when  cooled,  25  c.c.  of  ^  acid  are  added ;  the  mixture  heated  to  expel  CO-, 
and  filtered ;  after  washing  the  residue,  the  filtrate  and  washings  are  exactly 


§    20.  ACETIC    ACID.  83 

titrated  with  yV  alkali ;  the  volume  so  used  equals  the  amount  of  mineral 
acid  present  in  the  50  c.c.  of  vinegar. 

1  c.c.  T^  alkali=0-0049  gm.  H2SO4  or  0'003637  gin.  HC1. 

If  the  vinegar  contains  more  than  Qr2  per  cent,  of  mineral  acid, 
more  than  25  c.c.  of  -^  alkali  must  be  used  to  the  50  c.c.  vinegar 
before  evaporating  and  igniting. 

2.  Acetates    of    the    Alkalies    and   Earths. — These     salts     are 
converted  by  ignition  into  carbonates,  and  can  be  then  residually 
titrated  with  normal  acid ;  no  other  organic  acids  must  be  present, 
nor  must  nitrates,  or  similar  compounds  decomposable  by  heat. 
1  c.c.  normal  acid  =  0 '06  gm.  acetic  acid. 

3.  Metallic  Acetates. — Neutral  solutions  of    lead  and  iron  acetates 
may  be  precipitated  by  an  excess  of  normal  sodic  or  potassic  carbonate,  the 
precipitate  well  boiled,  filtered,  and  washed  with  hot  water,  the  filtrate  and 
washings  made  up  to  a  definite  volume,  and  an  aliquot  portion  titrated  with 
N  or  yV  acid ;  the  difference  between  the  quantity  so  used  and  calculated  for 
the  original  volume  of  alkali  will  represent  the  acetic  acid. 

If  such  solutions  contain  free  acetic  or  mineral  acids,  they  must 
be  exactly  neutralized  previous  to  treatment. 

If  other  salts  than  acetates  are  present,  the  process  must  be 
modified  as  follows  : — 

Precipitate  with  alkaline  carbonate  in  excess,  exactly  neutralize  with 
hydrochloric  acid,  evaporate  the  whole  or  part  to  dryness,  ignite  to  convert 
the  acetates  into  carbonates,  then  titrate  residually  with  normal  acid.  Any 
other  organic  acid  than  acetic  will,  of  course,  record  itself  in  terms  of  acetic 
acid. 

4.  Commercial  Acetate  of  Lime. — The   methods   just  described 
are  often  valueless  in  the  case  of  this  substance,  owing  to  tarry 
matters,  which  readily  produce  an  excess  of  carbonates. 

Fresenius  (Z.  a.  C.  xiii.  153)  adopts  the  following  process  for  tolerably 
pure  samples : — 5  gm.  are  weighed  and  transferred  to  a  250  c.c.  flask, 
dissolved  in  about  150  c.c.  of  water,  and  70  c.c.  of  normal  oxalic  acid  added ; 
the  flask  is  then  well  shaken,  and  filled  to  the  mark,  2  c.c.  of  water  are  added 
to  allow  for  the  volume  occupied  by  the  precipitate,  the  whole  is  again  well 
shaken,  and  left  to  settle.  The  solution  is  then  filtered  through  a  dry  filter 
into  a  dry  flask :  the  volume  so  filtered  must  exceed  200  c.c. 

100  c.c.  are  first  titrated  with  normal  alkali  and  litmus;  or,  if  highly 
coloured,  by  help  of  litmus  or  turmeric  paper ;  the  volume  used  multiplied 
by  2' 5  will  give  the  volume  for  5  gm. 

Another  100  c.c.  are  precipitated  with  solution  of  pure  calcic  acetate  in 
slight  excess,  warmed  gently,  the  precipitate  allowed  to  settle  somewhat, 
then  filtered,  well  washed,  dried,  and  strongly  ignited,  in  order  to  convert 
the  oxalate  into  calcic  carbonate  or  oxide,  or  a  mixture  of  both.  The  residue 
so  obtained  is  then  decomposed  with  excess  of  normal  acid,  and  titrated 
residually  with  normal  alkali.  By  deducting  the  volume  of  acid  used  to 
neutralize  the  precipitate  from  that  of  the  alkali  used  in  the  first  100  c.c., 
and  multiplying  by  2'5,  is  obtained  the  volume  of  alkali  expressing  the 
weight  of  acetic  acid  in  the  5  gm.  of  acetate. 

G  2 


8-4  VOLUMETRIC  ANALYSIS.  §    20. 

In  the  case  of  very  impure  and  highly  coloured  samples  of 
acetate,  it  is  only  possible  to  estimate  the  acetic  acid  by  repeated 
distillations  with  phosphoric  acid  and  water  to  incipient  dryness, 
and  then  titrating  the  acid  direct  with  •—  alkali,  each  c.c.  of  which 
represents  0*006  gm.  acetic  acid. 

The  distillation  is  best  arranged  as  suggested  by  Still  we  11  and 
Gladding,  or  later  by  Harcourt  Phillips  (C.  N,  liii.  181). 

A  100  to  120  c.c.  retort,  the  tubulure  of  which  carries  a  small  funnel 
fitted  in  with  a  caoutchouc  stopper,  and  the  neck  of  the  funnel  stopped 
tightly  with  a  glass  rod  shod  with  elastic  tube,  is  supported  upon  a  stand  in 
such  a  way  that  its  neck  inclines  upwards  at  about  forty-five  degrees :  the  end 
of  the  neck  is  drawn  out,  and  bent  so  as  to  fit  into  the  condenser  by  help  of 
an  elastic  tube.  The  greater  part  of  the  retort  neck  is  coated  with  flannel,  so 
as  to  prevent  too  much  condensation. 

1  gm.  of  the  sample  being  placed  in  the  retort,  10  c.c.  of  a  40  per  cent, 
solution  of  P2O5  is  added,  together  with  as  much  water  as  will  make  about 
50  c.c.  A  small  naked  flame  is  used,  and  if  carefully  manipulated,  the 
distillation  may  be  carried  on  to  near  dryness  without  endangering  the 
retort.  After  the  first  operation  the  retort  is  allowed  to  cool  somewhat,  then 
50  c.c.  of  hot  water  added  through  the  funnel,  another  distillation  made  as 
before,  and  the  same  repeated  a  third  time,  which  will  suffice  to  carry 
over  all  the  acetic  acid.  The  distillate  is  then  titrated  with  alkali  and 
phenolphthalein. 

By  this  arrangement  the  frothing  and  spirting  is  of  no  con- 
sequence, and  the  whole  process  can  be  completed  in  less  than 
an  hour.  The  results  are  excellent  for  technical  purposes. 

Weber  (Z.  a.  C.  xxiv.  614)  has  devised  a  ready  and  fairly  accurate 
method  of  estimating  the  real  acetic  acid  in  samples  of  acetate 
of  lime,  based  on  the  fact  that  acetate  of  silver  is  insoluble  in 
alcohol. 

The  Analysis  :  10  gm.  of  the  sample  in  powder  is  placed  in  a  250  c.c.  flask, 
a  little  water  added,  and  heated  till  all  soluble  matters  are  extracted,  cooled, 
and  made  up  to  the  measure :  25  c.c.  are  then  filtered  through  a  dry  filter, 
put  into  a  beaker,  50  c.c.  of  absolute  alcohol  added,  and  the  acetic  acid  at 
once  precipitated  with  an  alcoholic  solution  of  silver  nitrate.  The  silver 
acetate,  together  with  any  chloride,  sulphate,  etc.,  separates  free  from  colour. 
The  precipitate  is  brought  on  a  filter,  well  washed  with  60  per  cent,  alcohol 
till  the  free  silver  is  removed ;  precipitate  is  then  dissolved  in  weak  nitric 
acid,  and  titrated  with  ^  salt  solution.  Each  c.c.  represents  O'OOG  gm. 
acetic  acid. 

Several  trials  made  in  comparison  with  the  distillation  method 
with  phosphoric  acid  gave  practically  the  same  results. 

A  good  technical  process  has  been  devised  by  Grimshaw 
(Allen's  Organic  Analysis  i.  397).  10  gm.  of  the  sample  is  treated 
with  water  and  an  excess  of  sodic  bisulphate  (NaHSO4),  the 
mixture  diluted  to  a  definite  volume,  filtered,  and  a  measured 
portion  of  the  filtrate  titrated  with  standard  alkali ;  a  similar 
portion  meanwhile  is  evaporated  to  dryness  with  repeated  moisten- 
ing .with  water,  to  drive  off  all  free  acetic  acid.  The  residue  is 


§    21.  CITRIC    ACID.  85 

dissolved  and  titrated  with  standard  alkali,  when  the  difference 
between  the  volume  now  required  and  that  used  in  the  original 
solution  will  correspond  to  the  acetic  acid  in  the  sample.  Litmus 
paper  is  the  proper  indicator. 


CITRIC    ACID. 


§  21.  THIS  acid  in  the  free  state  may  readily  be  titrated 
with  pure  normal  soda  and  phenolphthalein.  1  c.c.  normal  alkali 
=  0*07  gm.  crystallized  citric  acid. 

1.  Citrates   of  the  Alkalies  and  Earths.  —  These    citrates    may    be 
treated  with  neutral  solution  of  lead  nitrate  or  acetate,  in  the  absence  of 
other  acids  precipitable  by  lead.     The  lead  citrate  is  washed  with  a  mixture 
of  equal  parts  alcohol  and  water,  the  precipitate  suspended  in  water,  and 
H-S  passed  into  it  till  all  the  lead  is  converted  into  sulphide;   the  clear 
liquid  is  then  boiled  to  remove  H2S,  and  titrated  with  normal  alkali. 

2.  Fruit  Juices,  etc.  —  If  tartaric  is  present,  together  with  free 
citric  acid,   the  former   is   first  separated   as   potassic  bitartrate, 
which  can  very  well  be  done  in  the  presence  of   citric  acid,  as 
follows  :  — 

A  cold  saturated  proof  spirit  solution  of  potassic  acetate  is  added  to  a 
somewhat  strong  solution  of  the  mixed  acids  in  proof  spirit,  in  sufficient 
quantity  to  separate  all  the  tartaric  acid  as  bitartrate,  which  after  stirring 
well  is  allowed  to  stand  some  hours;  the  precipitate  is  then  transferred  to  a 
filter,  and  first  washed  with  proof  spirit,  then  rinsed  off  the  filter  with  a  cold 
saturated  solution  of  potassic  bitartrate,  and  allowed  to  stand  some  hours, 
with  occasional  stirring;  this  treatment  removes  any  adhering  citrate.  The 
bitartrate  is  again  brought  on  to  a  filter,  washed  once  with  proof  spirit,  then 
dissolved  in  hot  water,  and  titrated  with  normal  alkali,  1  c.c.  of  which= 
0'15  gm.  tartaric  acid. 

The  first  filtrate  may  be  titrated  for  the  free  citric  acid  present  after 
evaporating  the  bulk  of  the  alcohol. 

3.  Lime  and  Lemon  Juices.  —  The  citric  acid  contained  in  lemon, 
lime,  and  similar  juices,  may  be  very  fairly  estimated  by 
Warington's  method  (J.  O.  S.  1875,  934). 

15  or  20  c.c.  of  ordinary  juice,  or  3  —  4  c.c.  of  concentrated  juice,  are  first 
exactly  neutralized  with  pure  normal  soda,  made  up,  if  necessary,  to  about 
50  c.c.,  heated  to  boiling  in  a  salt  bath,  and  so  much  solution  of  calcic 
chloride  added  as  to  be  slightly  in  excess  of  the  organic  acids  present.  The 
mixture  is  kept  at  the  boiling  point  for  about  half-an-hour,  the  precipitate 
collected  on  a  filter  and  washed  with  hot  water,  filtrate  and  washings  concen- 
trated to  about  15  c.c.,  and  a  drop  of  ammonia  added  ;  this  will  produce  a 
further  precipitate,  which  is  collected  separately  on  a  very  small  filter  by 
help  of  the  previous  filtrate,  then  washed  with  a  small  quantity  of  hot  water. 
Both  filters,  with  their  precipitates,  are  then  dried,  ignited  at  a  low  red  heat, 
and  the  ash  titrated  with  normal_or  ^  acid,  each  c.c.  of  which  represents 
respectively  0'07  or  0'007  gm  H3  Ci  +  H2O. 


86  VOLUMETRIC  ANALYSIS.  §    22. 

OXALIC  ACID. 

C2H2042H20=126. 

§  22.  THE  free  acid  can  be  accurately  titrated  with  normal 
alkali  and  phenolphthalein. 

In  combination  with  alkalies,  the  acid  can  be  precipitated  with  calcic 
chloride  as  calcic  oxalate,  where  no  other  matters  occur  precipitable  by 
calcium ;  if  acetic  acid  is  present  in  slight  excess  it  is  of  no  consequence,  as 
it  prevents  the  precipitation  of  small  quantities  of  sulphates.  The  precipi- 
tate is  well  washed,  dried,  ignited,  and  titrated  with  normal  acid,  1  c.c.  of 
which=0-063  gm.  O. 

Acid  oxalates  are  titrated  direct  for  the  amount  of  free  acid. 
The  reaction  continues  to  be  acid  until  alkali  is  added  in  such 
proportion  that  1  molecule  acid  =  2  atoms  alkali  metal. 

The  combined  acid  may  be  found  by  igniting  the  salt,  and 
titrating  the  residual  alkaline  carbonate  as  above. 

The  estimation  of  oxalic  acid  in  various  combinations  by 
permanganate  is  fully  explained  in  §  §  30.2  (c)  and  48. 


PHOSPHORIC    ACID. 

P205=142. 

§  23.  FREE  tribasic  phosphoric  acid  cannot  be  titrated  directly 
with  normal  alkali  in  the  same  manner  as  most  free  acids,  owing  to 
the  fact,  that  when  an  alkaline  base  (soda,  for  instance)  is  added  to 
the  acid,  a  combination  occurs  in  which  at  one  and  the  same  time 
red  litmus  paper  is  turned  blue  and  blue  red.  This  fact  has  been 
repeatedly  noticed  in  the  case  of  some  specimens  of  urine,  also  in 
milk.  In  order,  therefore,  to  estimate  phosphoric  acid,  or  alkaline 
phosphates,  alkalimetrically,  it  is  necessary  to  prevent  the  formation 
of  soluble  phosphate  of  alkali,  and  to  bring  the  acid  into  a  definite 
compound  with  an  alkaline  earth.  Such  a  method  gives  tolerably 
good  results  when  carried  out  as  follows  : — 

The  solution  of  free  acid,  or  its  acid  or  neutral  combination  with  alkali  in 
a  somewhat  dilute  state,  is  placed  in  a  flask,  and  a  known  volume  of  normal 
alkali  in  excess  added,  in  order  to  convert  the  whole  of  the  acid  into  a  basic 
salt;  a  drop  or  two  of  rosolic  acid  is  added,  then  sufficient  neutral  baric 
chloride  poured  in  to  combine  with  all  the  phosphoric  acid,  the  mixture  is 
heated  nearly  to  boiling ;  and,  while  hot,  the  excess  of  alkali  is  titrated  with 
normal  acid.  The  suspended  baric  phosphate,  together  with  the  liquid, 
possesses  a  rose-red  colour  until  the  last  drop  or  two  of  acid,  after  continuous 
heating  and  agitation,  gives  a  permanent  white  or  slightly  yellowish,  milky 
appearance,  when  the  process  is  ended. 

The  volume  of  normal  alkali,  less  the  volume  of  acid,  represents  the 
amount  of  alkali  required  to  convert  the  phosphoric  acid  into  a  chemically 
neutral  salt,  e.g.  trisodic  phosphate.  1  c.c.  alkali  =  0'02366  gm.  P2O5.  In 
dealing  with  small  quantities  of  material,  it  is  better  to  use  |  or  ^5-  standard 
solutions. 


§    24.  PHOSPHORIC    ACID.  87 

Thompson  has  shown  in  his  researches  on  the  indicators,  that 
phosphoric  acid,  either  in  the  free  state,  or  in  combination  with 
soda  or  potash,  may  with  very  fair  accuracy  be  estimated  by  the 
help  of  methyl  orange  and  phenolphthalein.  If,  for  instance, 
normal  potash  be  added  to  a  solution  of  phosphoric  acid  until  the 
pink  colour  of  methyl  orange  is  discharged,  KH2P04  is  formed 
(112  KHO=H2  P205).  If  now  phenolphthalein  is  added,  and 
the  addition  of  potash  continued  until  a  red  colour  occurs,  K2HP04 
is  formed.  (Again  112  KHO  =  142  P205.)  On  adding  standard 
hydrochloric  or  sulphuric  acid,  until  the  pink  colour  of  methyl 
orange  reappears,  the  titration  with  standard  potash  may  be 
repeated. 

Many  attempts  have  been  made  to  utilize  these  reactions  for  the 
accurate  estimation  of  P205  in  manures,  etc.,  but,  so  far  as  my 
own  experience  goes,  without  adequate  success. 

Titration  as  Ammonio-magrnesian  Phosphate. — Stolba  (Clietll. 
Cent.  1866,  727,  728)  adopts  an  alkalimetric  method,  which 
depends  upon  the  fact,  that  one  molecule  of  the  double  salt 
requires  two  molecules  of  a  mineral  acid  for  saturation. 

The  precipitation  is  made  with  magnesia  mixture,  well  washed  with 
ammonia,  and  the  latter  completely  removed  by  washing  with  alcohol  of 
50  or  60  per  cent.  The  precipitate  is  then  dissolved  in  a  measured  excess 
of  TTT  acid,  methyl  orange  added,  and  the  amount  of  acid  required  found  by 
titration  with  T^  alkali.  Care  must  be  taken  that  all  free  ammonia  is 
removed  from  the  filter  and  precipitate,  and  that  the  whole  of  the  double 
salt  is  decomposed  by  the  acid  before  titration,  which  may  always  be  insured 
by  using  a  rather  large  excess  and  warming.  The  titration  is  carried  on  cold. 

This  method  has  given  me  very  good  results  in  comparison  with 
the  gravimetric  method.  The  same  process  is  applicable  to  the 
estimation  of  arsenic  acid,  and  also  of  magnesia. 

1  c.c.  of  fV  acid  =  0-00355  gin.  P205 
=  0-00575  gm.  As203 
=  0-002       gm.  MgO 

The  reaction  in  the  case  of  phosphoric  acid  may  be  expressed  as 
follows : — 

Mg  (XH4)  PO4  +  2HC1  -  (XH4)  H2P04  +  MgCl2. 


SULPHURIC     ANHYDRIDE. 

SO3  =  80. 

§  24.  XORDHAUSEN  or  fuming  sulphuric  acid  consists  of  a 
mixture  of  SO3  and  H2S04.  When  it  is  rich  in  SO3  it  occurs  in 
a  solid  form,  and  being  very  hygroscopic  cannot  be  weighed  in  the 
ordinary  manner.  Its  strength  is  therefore  best  taken  in  the  wray 
recommended  by  Messel  as  follows  : — A  very  thin  bulb  tube  with 
capillary  ends  is  inserted  into  a  bottle  of  the  melted  acid.  The 


88  VOLUMETRIC   ANALYSIS.  §    25. 

ends  are  bent  like  the  letter  /,  the  bulb  being  in  the  middle.  The 
bottle  should  be  of  such  size,  that  one  end  of  the  tube  projects  out 
of  its  mouth.  As  soon  as  the  bulb  is  filled,  the  upper  capillary 
end  is  sealed,  the  tube  lifted  out,  wiped,  inverted,  and  the  other 
end  sealed ;  the  tube  is  then  carefully  wiped  with  blotting  paper 
till  dry  and  clean,  then  weighed.  A  stoppered  bottle,  just  large 
enough  to  allow  the  tube  being  placed  loosely  inside  it,  is  then 
about  one-third  filled  with  water,  the  tube  gently  inserted,  the 
stopper  replaced,  held  firmly  in  by  the  hand,  and  a  vigorous  shake 
given  so  as  to  break  the  tube.  A  sudden  vibration  occurs  from 
contact  of  the  acid  with  the  water,  but  no  danger  is  incurred. 
A  white  cloud  is  seen  on  the  sides  of  the  bottle,  which  disappears 
on  shaking  for  a  few  minutes.  After  the  bottle  is  cooled  the 
contents  are  emptied  into  a  measuring  flask.  An  aliquot  portion 
is  then  taken  out  and  titrated  with  •-$  iodine  for  SO2,  which  is 
always  present  in  small  quantity  :  another  portion  is  titrated  with 
standard  alkali  and  methyl  orange  for  sulphuric  acid. 


TARTARIC    ACID. 

C4H606=150. 

<•§  25.     THE  free  acid  may  be  readily  titrated  with  normal  alkali 
and  phenolphthalein. 

1  c.c.  alkali  =  0 '07 5  gm.  tartaric  acid. 

The  amount  of  tartaric  acid  existing  in  tartaric  acid  liquors  is 
best  estimated  by  precipitation  as  potassic  bitartrate ;  the  same  is 
also  the  case  with  crude  argols,  lees,  etc.  Manufacturers  are  highly 
indebted  to  War  ing  ton  and  Grosjean  for  most  exhaustive 
papers  on  this  subject,  to  which  reference  should  be  made  by  all 
who  desire  to  study  the  nature  and  analysis  of  all  commercial  com- 
pounds of  citric  and  tartaric  acids  (War  ing  ton,  /.  C.  S.  1875, 
925—994;  Grosjean,  /.  C.  S.  1879,  341—356). 

Without  entering  into  the  copious  details  and  explanations  given 
by  these  authorities,  the  methods  may  be  summarized  as  follows  : — 

1.     Commercial   Tartrates. 

In  the  case  of  good  clean  tartars,  even  though  ihey  may  contain  sulphates 
and  carbonates,  very  accurate  results  may  be  obtained  by  indirect  methods. 

(a)  The  very  finely  powdered  sample  is  first  titrated  with  normal  alkali, 
and  thus  the  amount  of  tartaric  acid  existing  as  bitartrate  is  found ;  another 
portion  of   the  sample   is  then  calcined   at  a  moderate   heat,  and   the  ash 
titrated.    By  deducting  from  the  volume  of  acid  so  used  the  volume  used 
for  bitartrate,   the  amount  of  base   corresponding  to   neutral   tartrates  is- 
obtained. 

(b)  The  whole  of  the  tartaric  acid  is  exactly  neutralized  with  caustic 
soda,  evaporated  to  dryness,  calcined,  and  the  ash  titrated  with  normal  acid ; 
the  total  tartaric  acid  is  then  calculated  from  the  volume  of  standard  acid 
used;   any  other  organic  acid  present  will  naturally  be  included  in  this 


8    25."  TARTAHIC    ACID.  89 

o 

amount.     In  the  case  of  fairly  pure  tartars,  etc.,  this  probable  error  may  be 
disregarded. 

Waring  ton's  description  of  the  first  process  is  as  follows  : — 

5  gm.  of  the  finely  powdered  tartar  are  heated  with  a  little  water  to 
dissolve  any  carbonates  that  may  be  present.  If  it  is  wished  to  guard  against 
crystalline  carbonates,  5  c.c.  of  standard  HC1  are  added  in  the  first  instance, 
and  the  heating  is  conducted  in  a  covered  beaker.  Standard  alkali  is  next 
added  to  the  extent  of  about  three-fourths  of  the  amount  required  by  a  good 
tartar  of  the  kind  examined,  plus  that  equivalent  to  the  acid  used,  and  the 
whole  is  brought  to  boiling;  when  nearly  cold,  the  titration  is  finished. 
From  the  amount  of  alkali  consumed,  minus  that  required  by  the  HC1,  the 
tartaric  acid  present  as  acid  tartrate  is  calculated. 

.2  gm.  of  the  powdered  tartar  are  next  weighed  into  a  platinum  crucible 
with  a  well-fitting  lid ;  the  crucible  is  placed  over  an  argand  burner ;  heat  is 
first  applied  very  gently  to  dry  the  tartar,  and  then  more  strongly  till 
inflammable  gas  ceases  to  be  evolved.  The  heat  should  not  rise  above  very 
low  redness.  The  black  ash  is  next  removed  with  water  to  a  beaker.  If  the 
tartar  is  known  to  be  a  good  one,  20  c.c.  of  standard  H2SO4  are  now  run 
from  a  pipette  into  the  beaker,  a  portion  of  the  acid  being  used  to  rinse  the 
crucible.  The  contents  of  the  beaker  are  now  brought  to  boiling,  filtered, 
and  the  free  acid  determined  with  standard  alkali.  As  the  charcoal  on  the 
filter  under  some  circumstances  retains  a  little  acid,  even  when  well  washed, 
it  is  advisable  when  the  titration  is  completed  to  transfer  the  filter  and  its 
contents  to  the  neutralized  fluid,  and  add  a  further  amount  of  alkali  if 
necessary.  From  the  neutralizing  power  of  a  gram  of  burnt  tartar  is 
subtracted  the  acidity  of  a  gram  of  unburnt  tartar,  both  expressed  in  c.c.  of 
standard  alkali,  the  difference  in  the  neutralizing  power  of  the  bases  existing 
as  neutral  tartrates,  and  is  then  calculated  into  tartaric  acid  on  this 
assumption.* 

If  the  tartar  is  of  low  quality,  5  c.c.  of  solution  of  hydrogen  peroxide 
(1  volume=10  volumes  O)  are  added  to  the  black  ash  and  water,  and 
immediately  afterwards  the  standard  acid ;  the  rest  of  the  analysis  proceeds 
as  already  described ;  the  small  acidity  usually  belonging  to  the  peroxide 
solution  must,  however,  be  known  and  allowed  for  in  the  calculation.  By 
the  use  of  hydrogen  peroxide  the  sulphides  formed  during  ignition  are 
reconverted  into  sulphates,  and  the  error  of  excess  which  their  presence 
would  occasion  is  avoided. 

The  above  method  does  not  give  the  separate  amounts  of  acid 
and  neutral  tartrates  in  the  presence  of  carbonates,  but  it  gives  the 
correct  amount  of  tartaric  acid ;  it  is  also  correct  in  cases  where 
free  tartaric  acid  exists,  so  long  as  the  final  results  show  that  some 
acid  existed  as  neutral  salt.  Whenever  this  method  shows  that 
the  acidity  of  the  original  substance  is  greater  than  the  neutralizing 
power  of  the  ash,  it  will  be  necessary  to  use  the  method  b,  which 
is  the  only  one  capable  of  giving  good  results  when  the  sample 
contains  much  free  tartaric  acid. 

Instead  of  the  alkalimetric  estimation  in  both  the  above  methods, 
equally  good  results  may  be  got  by  a  carbonic  acid  determination 

*  It  is  obvious  that  the  neutralizing  power  of  the  ash  of  an  acid  tartrate  is  exactly 
the  same  as  the  acidity  of  the  same  tartrate  before  burning1.  In  making  the  calcula- 
tions, it  must  be  remembered  that  the  value  of  the  alkali  in  tartaric  acid  is  twice  as 
great  in  the  calculation  made  from  the  acidity  of  the  unburnt  tartar,  as  in  the 
calculation  of  the  acid  existing  as  neutral  tartrates. 


90  VOLUMETRIC  ANALYSIS.  §    25. 

in  the  ash  with  Scheibler's  apparatus  (§  26.6),  or  any  of  the 
usual  methods. 

2.      Tartaric    Acid    Liquors. 

Old  factory  liquors  contain  a  great  variety  of  substances  gradually 
accumulated,  from  which  the  actual  tartaric  acid  can  only  be 
separated  as  bitartrate  by  the  following  process  : — 

(c)  A  quantity  of  liquor  containing  2—4  gm.  of  tartaric  acid,  and  of 
30 — 40  c.c.  volume,  is  treated  with  a  saturated  solution  of  neutral  potassic 
citrate,  added  drop  by  drop  with  constant  stirring.  If  free  sulphuric  acid  is 
present  no  precipitate  is  at  first  produced  ;  but  as  soon  as  the  acid  is  satisfied, 
the  bitartrate  begins  to  appear  in  streaks  on  the  sides  of  the  vessel.  "When 
this  is  seen,  the  remainder  of  the  citrate  is  measured  in  to  avoid  an  undue 
excess :  4  c.c.  of  a  saturated  solution  of  potassic  citrate  will  be  found 
sufficient  to  precipitate  the  maximum  of  4  grams  of  tartaric  acid  supposed  to 
be  present.  If  the  liquor  contain  a  great  deal  of  sulphuric  acid,  a  fine 
precipitate  of  potassic  sulphate  will  precede  the  formation  of  bitartrate,  but 
is  easily  distinguished  from  it.  With  liquors  rich  in  sulphuric  acid,  it  is 
advisable  to  stir  the  mixture  vigorously  at  intervals  for  half  an  hour,  then 
proceed  as  in  3  d. 

Grosjean  modifies  this  process  by  precipitating  the  liquor  with  an  excess 
of  calcic  carbonate,  then  boiling  the  mixture  with  excess  of  potassic  oxalate. 
By  this  means  the  alumina,  iron,  phosphoric  and  sulphuric  acids  are  thrown 
down  with  the  calcic  oxalate,  and  the  precipitate  allows  of  ready  filtration. 
The  separation  as  bitartrate  then  follows,  as  in  d. 


3.      Very    impure    Lees    and    Argrols. 

Grosjean  (/.  C.  S.  1879,  341)  gives  a  succinct  method  for 
the  treatment  of  these  substances,  based  on  War  ing  ton's  original 
oxalate  process,  the  principle  of  which  is  as  follows  : — 

The  finely  ground  sample  (=about  2  gm.  tartaric  acid)  is  first  moistened 
with  a  little  water,  heated  to  100°  C.,  then  digested  for  15  minutes  or  so  with 
an  excess  of  neutral  potassic  oxalate  (the  excess  must  not  be  less  than 
1*5  gm.),  and  nearly  neutralized  with  potash.  After  repeated  stirring,  the 
mixture  is  transferred  to  a  vacuum  filter,  and  the  residue  washed ;  the 
liquid  so  obtained  contains  all  the  tartaric  acid  as  neutral  potassic  tartrate ; 
excess  of  citric  acid  is  added,  which  precipitates  the  whole  of  the  tartaric 
acid  as  bitartrate,  and  the  amount  is  found  by  titration  with  standard  alkali 
in  the  usual  way. 

One  of  the  chief  difficulties  in  treating  low  qualities  of  material  is  the 
filtration  of  the  nearly  neutral  mixture  above  mentioned.  Grosjeau  adopts 
the  principle  of  Casamajor's  filter  (C.  N.  xxxii.  45),  using  an  ordinary 
funnel  with  either  platinum,  lead,  or  pumice  disc ;  but  whether  this,  or 
Bun  sen's,  or  other  form  of  filter  is  used,  the  resulting  filtrate  and  washings 
(which  for  2  gm.  tartaric  acid  should  not  much  exceed  50  c.c.)  are  ready  for 
the  separation  of  the  bitartrate  in  the  following  improved  way : — 

(d)  To  the  50  c.c.  or  so  of  cold  solution  5  gm.  of  powdered  potassic 
chloride  is  added,  and  stirred  till  dissolved:  this  renders  the  subsequent 
precipitation  of  bitartrate  very  complete.  A  50-per-cent.  solution  of  citric 
acid  is  then  mixed  with  the  liquid  in  such  proportion,  that  for  every  2  gm. 
of  tartaric  acid  an  equal,  or  slightly  greater  amount  of  citric  acid  is  present. 
By  continuously  stirring,  the  whole  of  the  bitartrate  comes  down  in  ten 


DYER. 


§    26.  CARBONIC    ACID.  91 

minutes  (Grosjean) ;  if  the  temperature  is  much  above  16°,  it  is  preferable 
to  wait  half  an  hour  or  so  before  filtering.  This  operation  is  best  done  on 
the  vacuum  filter,  and  the  washing  is  made  with  a  5-per-cent.  solution  of 
potassic  chloride,  saturated  at  ordinary  temperature  with  potassic  bitartrate ; 
if  great  accuracy  is  required,  the  exact  acidity  of  the  solution  should  be 
found  by  ^  alkali,  and  the  washing  continued  until  the  washings  show  no 
greater  acidity,  thus  proving  the  absence  of  citric  acid.  Finally,  the  washed 
precipitate  is  gently  pressed  into  a  cake  to  free  it  from  excess  of  liquid, 
transferred  to  a  beaker  with  the  filter,  hot  water  added,  and  titrated  with 
standard  alkali. 

The  troublesome  filtration  can  be  avoided  in  many  cases  by  taking 
30 — 40  gm.  of  substance,  and  after  decomposition  by  oxalate,  and  neutralizing 
with  potash,  making  up  the  volume  to  150  or  200  c.c.,  adding  water  in 
corresponding  proportion  to  the  bulk  of  the  residue,  then  taking  an  aliquot 
portion  for  precipitation.  A  blank  experiment  made  by  Grosjean  in  this 
way,  gave  a  volume  of  375  c.c.  for  the  residue  in  10  gm.  lees.  Other  things 
being  equal,  therefore,  30  or  40  gm.  may  respectively  be  made  up  to  161  and 
215  c.c.,  then  50  c.c.  taken  for  precipitation. 


CARBONIC    ACID    AND    CARBONATES. 

§  26.  ALL  carbonates  are  decomposed  by  strong  acids ;  the 
carbonic  acid  which  is  liberated  splits  up  into  water  and  carbonic 
anhydride  (CO2),  which  latter  escapes  in  the  gaseous  form. 

It  will  be  readily  seen  from  what  has  been  said  previously  as 
to  the  estimation  of  the  alkaline  earths,  that  carbonic  acid  in 
combination  can  be  estimated  volumetrically  with  a  very  high 
degree  of  accuracy  (see  §  17). 

The  carbonic  acid  to  be  estimated  may  be  brought  into 
combination  with  either  calcium  or  barium,  these  bases  admitting 
of  the  firmest  combination  as  neutral  carbonates. 

If  the  carbonic  acid  exist  in  a  soluble  form  as  an  alkaline  mono- 
carbonate,  the  decomposition  is  effected  by  the  addition  of  baric  or 
calcic  chloride  as  before  directed ;  if  as  bicarbonate,  or  a  compound 
between  the  two,  ammonia  must  be  added  with  either  of  the 
chlorides. 

As  solution  of  ammonia  frequently  contains  carbonic  acid,  this 
must  be  removed  by  the  aid  of  baric  or  calcic  chloride,  previous 
to  use. 

1.      Carbonates    Soluble    in    Water. 

It  is  necessary  to  remember,  that  when  calcic  chloride  is  used  as 
the  precipitant  in  the  cold,  amorphous  calcic  carbonate  is  first 
formed ;  and  as  this  compound  is  sensibly  soluble  in  water,  it  is 
necessary  to  convert  it  into  the  crystalline  form.  In  the  absence  of 
free  ammonia  this  can  be  accomplished  by  boiling.  When  ammonia 
is  present,  the  same  end  is  obtained  by  allowing  the  mixture  to 
stand  for  eight  or  ten  hours  in  the  cold,  or  by  heating  for  an  hour 
or  two  to  70 — 80°  C.  With  barium  the  precipitation  is  regular. 

Another  fact  is,  that  when  ammonia  is  present,  and  the  precipi- 
tation occurs  at  ordinary  temperatures,  ammonic  carbamate  is 


92  VOLUMETKI C  ANALYSIS.  §    26. 

formed,  and  the  baric  or  calcic  carbonate  is  only  partially  precipi- 
tated. This  is  overcome  by  heating  the  mixture  to  near  boiling  for 
a  couple  of  hours,  and  is  best  done  by  passing  the  neck  of  the 
flask  through  a  retort  ring,  and  immersing  the  flask  in  boiling 
water. 

When  caustic  alkali  is  present  in  the  substance  to  be  examined, 
it  is  advisable  to  use  barium  as  the  precipitant ;  otherwise,  for  all 
volumetric  estimations  of  CO2  calcium  is  to  be  preferred,  because 
the  precipitate  is  much  more  quickly  and  perfectly  washed  than 
the  barium  compound. 

Example:  1  gm.  of  pure  anhydrous  sodic  carbonate  was  dissolved  in 
water,  precipitated  while  hot  with  baric  chloride,  the  precipitate  allowed  to 
settle  well,  the  clear  liquid  decanted  through  a  moist  filter,  more  hot  water 
containing  a  few  drops  of  ammonia  poured  over  the  precipitate,  which  was 
repeatedly  done  so  that  the  bulk  of  the  precipitate  remained  in  the  flask, 
being  washed  by  decantation  through  the  filter ;  when  the  washings  showed 
no  trace  of  chlorine,  the  filter  was  transferred  to,  the  flask  containing  the 
bulk  of  the  precipitate,  and  20  c.c.  of  normal  nitric  acid  added,  then  titrated 
with  normal  alkali,  of  which  1'2  c.c.  was  required =18'8  c.c.  of  acid ;  this 
multiplied  by  0'022,  the  coefficient  for  carbonic  acid,  gave  0'4136  gm.  CO2= 
41 '36  per  cent.,  or  multiplied  by  0'053,  the  coefficient  for  sodic  carbonate, 
gave  0'9964  gm.  instead  of  1  gm. 

2.      Carbonates    Soluble    in    Acids. 

It  sometimes  occurs  that  substances  have  to  be  examined  for 
carbonic  acid,  which  do  not  admit  of  being  treated  as  above 
described ;  such,  for  instance,  as  the  carbonates  of  the  metallic 
oxides  (white  lead,  calamine,  etc.),  carbonates  of  magnesia,  iron, 
and  copper,  the  estimation  of  carbonic  acid  in  cements,  mortar,  and 
many  other  substances.  In  these  cases  the  carbonic  acid  must  be 
evolved  from  the  combination  by  means  of  a  stronger  acid,  and 
conducted  into  an  absorption  apparatus  containing  ammonia,  then 
precipitated  with  calcic  chloride,  and  titrated  as  before  described. 

The  following  form  of  apparatus  (lig.  25)  aifords  satisfactory 
results. 

The  weighed  substance  from  which  the  carbonic  acid  is  to  be  evolved  is 
placed  in  b  with  a  little  water;  the  tube  d  contains  strong  hydrochloric 
acid,  and  c  broken  glass  wetted  with  ammonia  free  from  carbonic  acid. 
The  flask  a  is  about  one-eighth  filled  with  the  same  ammonia  :  the  bent  tube 
must  not  enter  the  liquid.  When  all  is  ready  and  the  corks  tight,  warm  the 
flask  a  gently  so  as  to  fill  it  with  vapour  of  ammonia,  then  open  the  clip  and 
allow  the  acid  to  flow  circumspectly  upon  the  material,  which  may  be  heated 
until  all  carbonic  acid  is  apparently  driven  off  ;  then  by  boiling  and  shaking 
the  last  traces  can  be  evolved,  and  the  operation  ended.  ~W  hen  cool,  the 
apparatus  may  be  opened,  the  end  of  the  bent  tube  washed  into  a,  and  also  a 
good  quantity  of  boiled  distilled  water  passed  through  c,  so  as  to  carry  down 
any  ammonic  carbonate  that  may  have  formed.  Then  add  solution  of  calcic 
chloride,  boil,  filter,  and  titrate  the  precipitate  as  before  described. 

During  the  filtration,  and  while  ammonia  is  present,  there  is  a  great 
avidity  for  carbonic  acid,  therefore  boiling  water  should  be  used  for  washing, 
and  the  funnel  kept  covered  with  a  small  glass  plate. 


CA11BONIC    ACID. 


93 


In  many  instances  CO2  may  be  estimated  by  its  equivalent  in 
chlorine  with  T^  silver  and  potassic  chromate,  as  shown  in  §  38. 


Pig.  25. 

3.      Carbonic    Acid    Gas    in    "Waters,    etc. 

The  carbonic  acid  existing  in  waters  as  neutral  carbonates  of  the 
alkalies  or  alkaline  earths  may  very  elegantly  and  readily  be  titrated 
directly  by  y^-  acid  (see  §  17). 

Well  or  spring  water,  and  also  mineral  waters,  containing  free 
carbonic  acid  gas,  can  be  examined  by  collecting  measured  quantities 
of  them  at  their  source,  in  bottles  containing  a  mixture  of  calcic 
and  animoiiic  chloride,  afterwards  heating  the  mixture  in  boiling 
water  for  one  or  two  hours,  and  titrating  the  precipitate  as  before 
described. 

Pettenkofer's  method  with  caustic  "Baryta  or  lime  is  decidedly 
preferable  to  any  other.  Lime  water  may  be  used  instead  of  baryta 
with  equally  good  results,  but  care  must  be  taken  that  the 
precipitate  is  crystalline. 

The  principle  of  the  method  is  that  of  removing  all  the  carbonic 
acid  from  a  solution,  or  from  a  water,  by  excess  of  baryta  or  lime 


94 


VOLUMETRIC  ANALYSIS. 


§    26. 


water  of  a  known  strength ;  and,  after  absorption,  finding  the 
excess  of  baryta  or  lime  by  titration  with  -^5-  acid  and  turmeric 
paper. 

The  following  is  the  best  method  to  be  pursued  for  ordinary 
drinking  waters  not  containing  large  quantities  of  carbonic  acid  : — 

100  c.c.  of  the  water  are  put  into  a  flask  with  3  c.c.  of  strong  solution  of 
calcic  or  baric  chloride,  and  2  c.c.  of  saturated  solution  of  ammonic  chloride ; 
45  c.c.  of  baryta  or  lime  water,  the  strength  of  which  is  previously  ascertained 
by  means  of  decinormal  acid,  are  then  added,  the  flask  well  corked  and  put 
aside  to  settle ;  when  the  precipitate  is  fully  subsided,  take  out  50  c.c.  of  the 
clear  liquid  with  a  pipette,  and  let  this  be  titrated  with  deciuormal  acid. 
The  quantity  required  must  be  multiplied  by  3  for  the  total  baryta  or  lime 
solution,  there  being  50  c.c.  only  taken;  the  number  of  c.c.  so  found  must  be 
deducted  from  the  original  quantity  required  for  the  baryta  solution  added ; 
the  remainder  multiplied  by  0'0022  will  give  the  weight  of  carbonic  acid 
existing  free  and  as  bicarbonate  in  the  100  c.c. 

The  addition  of  the  baric  or  calcic  chloride  and  ammonic  chloride  is  made 
to  prevent  any  irregularity  which  might  arise  from  alkaline  carbonates  or 
sulphates,  or  from  magnesia. 

If  it  be  desirable  to  ascertain  the  volume  of  carbonic  acid  from 
the  weight,  1000  c.c.  of  gas,  at  0°  and  076  m.m.,  weigh 
1 '96663  gm.  100  cubic  inches  weigh  47*26  grains. 


4.      Carbonic    Acid    in    Aerated    Beverages,    etc. 

For  ascertaining  the  quantity  of  carbonic  acid  in  bottled  aerated 
waters,  such  as  soda,  seltzer,  potass,  and  others,  the  following 
apparatus  is  useful. 


Fig.  26. 

Fig.  26  is  a  brass  tube  made  like  a  cork-borer,  about  five  inches  long,  having 
four  small  holes,  two  on  each  side,  and  about  two  inches  from  its  cutting  end ; 


§    26.  CARBONIC    ACID.  95 

the  upper  end  is  securely  connected  with  the  bent  tube  from  the  absorption 
flask  (fig.  27)  by  means  of  a  vulcanized  tube ;  the  flask  contains  a  tolerable 
quantity  of  pure  ammonia,  into  which  the  delivery  tube  dips ;  the  tube  a 
contains  broken  glass  moistened  with  ammonia. 

Everything  being  ready  the  brass  tube  is  greased,  and  the  bottle  being 
held  in  the  right  hand,  the  tube  is  screwed  a  little  aslant  through  the  cork 
by  turning  the  bottle  round,  until  the  holes  appear  below  the  cork  and  the 
gas  escapes  into  the  flask.  When  all  visible  action  has  ceased,  after  the 
bottle  has  been  well  shaken  two  or  three  times  to  evolve  all  the  gas  that  can 
be  possibly  eliminated,  the  vessels  are  quietly  disconnected,  the  tube  a  washed 
out  into  the  flask,  and  the  contents  of  the  bottle  added  also ;  the  whole  is 
then  precipitated  with  calcic  chloride  and  boiled,  and  the  precipitate  titrated 
as  usual.  This  gives  the  total  carbonic  acid  free  and  combined. 

To  find  the  quantity  of  the  latter,  another  bottle  of  the  same  manufacture 
must  be  evaporated  to  dryness,  and  the  residue  gently  ignited,  then  titrated 
with  normal  acid  and  alkali ;  the  amount  of  carbonic  acid  in  the  mono- 
carbonate  deducted  from  the  total,  will  give  the  weight  of  free  gas  originally 
present. 

The  volume  may  be  found  as  follows : — 1000  c.c.  of  carbonic  acid  at  0°, 
and  76  m.m.,  weigh  T96663  gm.  Suppose,  therefore,  that  the  total  weight 
of  carbonic  acid  found  in  a  bottle  of  ordinary  soda  water  was  2'8  gm.,  and 
the  weight  combined  with  alkali  0'42  gm.,  this  leaves  2'38  gm.  CO2  in 
a  free  state — 

1-96663  :  2'38  :  :  1000  :  x  =  1210  c.c. 

If  the  number  of  c.c.  of  carbonic  acid  found  is  divided  by  the 
number  of  c.c.  of  soda  water  contained  in  the  bottle  examined,  the 
quotient  will  be  the  volume  of  gas  compared  with  that  of  the  soda 
water.  The  volume  of  the  contents  of  the  bottle  is  ascertained  by 
marking  the  height  of  the  fluid  previous  to  making  the  experiment ; 
the  bottle  is  afterwards  filled  to  the  same  mark  with  water,  emptied 
into  a  graduated  cylinder  and  measured;  say  the  volume  was 
292  c.c.,  therefore 

1210 

-202-  =  4-14  vols.  CO2. 


5.      Carbonic    Acid    in    Air. 

A  glass  globe  or  bottle  capable  of  being  securely  closed  by  a 
stopper  or  otherwise,  and  holding  4  to  6  liters,  is  filled  with  the  air 
to  be  tested  by  means  of  a  bellows  aspirator ;  baryta  water  is  then 
introduced  in  convenient  quantity  and  of  known  strength  as 
compared  with  T|~j  acid.  The  vessel  is  securely  closed,  and  the 
liquid  allowed  to  flow  round  the  sides  at  intervals  during  half  an 
hour ;  if  at  the  end  of  that  time  no  great  amount  of  cloudiness  in 
the  baryta  has  occurred,  it  may  be  advisable  to  refill  the  bottle 
with  air  one  or  more  times.  This  can  of  course  be  done  with  the 
aspirator  as  at  first,  taking  care  on  each  occasion  to  agitate  the 
vessel,  so  as  to  bring  the  baryta  in  contact  with  all  parts  of  its 
surface  during  the  space  of  half  an  hour.  When  sufficient  air  has 
thus  been  treated,  the  baryta  is  emptied  out  quickly  into  a  beaker, 
the  bottle  rinsed  out  with  distilled  water  free  from  CO2,  the 


96  VOLUMETRIC   ANALYSIS.  §    26. 

rinsings  added  to  the  baryta,  and  the  excess  of  the  latter  at  once 
ascertained  by  T^y-  hydrochloric  acid  and  turmeric  paper  as  described 
in  §  14.9 ;  or,  instead  of  taking  the  whole  of  the  baryta,  that  and 
the  rinsings  may  be  emptied  into  a  stoppered  cylinder,  made  up  to 
a  definite  measure,  and  half  or  one-third  taken  for  titration.  The 
final  calculation  is  of  course  made  on  the  total  baryta  originally 
used,  and  upon  the  exact  measurement  of  the  air-collecting  vessel. 

It  is  above  all  things  necessary  to  prevent  the  absorption  of  CO2 
from  extraneous  sources  during  the  experiment.  The  error  may  be 
reduced  to  a  minimum  by  carrying  on  the  titration  in  the  vessel 
itself,  which  is  done  by  fixing  an  accurately  graduated  pipette 
through  the  cork  or  caoutchouc  stopper  of  the  air  vessel,  to  the 
upper  end  of  which  is  attached  a  stout  piece  of  elastic  tube,  closed 
with  a  pinch-cock ;  and  this  being  filled  to  the  0  mark  with  dilute 
standard  acid  acts  as  a  burette.  The  baryta  solution  is  placed  in 
the  air  bottle,  and  after  absorption  of  all  CO2,  a  few  drops  of 
phenolphtlialein  are  added  through  the  ventilator,  and  the  excess  of 
baryta  is  found  by  running  in  the  acid  until  the  colour  disappears. 

The  cork  or  stopper  must  have  a  second  opening  to  act  as 
ventilator ;  a  small  piece  of  glass  tube  does  very  well. 

If  a  freshly  made  solution  of  oxalic  acid  is  used  containing 
0-2863  gm.  per  liter,  each  c.c.  represents  1  mgni.  CO2.  The  liquid 
holds  its  strength  correctly  for  a  day,  and  can  be  made  as  required 
from  a  strong  solution,  say  28'636  gm.  per  liter. 

Another  method  of  calculation  is,  to  convert  the  volume  of 
baryta  solution  decomposed  into  its  equivalent  volume  in  ~  acid, 
1  c.c.  of  which  =  0'0022  gm.  CO2  or  by  measurement  at  0°  C.  and 
760  m.m.  pressure  represents  I'll 9  c.c.  The  method  here  described 
is  a  combination  of  those  of  Pettenkofer  and  Dal  ton,  and 
though  much  used,  is  liable  to  considerable  error  from  various 
causes.  Haldane  and  Pembrey  (C.  N.  lix.  256 — 269)  point  out 
that  at  the  Paris  Observatory  the  practice  is  to  absorb  the  CO2  in 
caustic  potash  through  a  series  of  tubes,  then  liberate  it  by  acid 
and  measure  as  gas.  They  describe  in  the  same  paper  a  gravimetric 
method  of  their  own,  which  gives  very  accurate  results,  and  which 
depends  on  absorption  of  the  gas  by  soda  lime  and  weighing  the 
increase. 

For  rough  sanitary  purposes  Angus  Smith,  many  years  ago, 
described  in  his  Air  and  liain  a  minimetric  method  of  estimating 
CO2  in  air ;  it  depended  on  the  principle  that  the  purer  the  air  the 
larger  the  volume  of  it  is  required  to  produce  turbidity  with  lime  or 
baryta  water;  this  method  was  open  to  the  objection  that  it  is 
difficult  to  tell  precisely  when  turbidity  occurs. 

Lunge  and  Zeckendorf  have  made  use  of  this  principle  with 
modifications,  which  appears  to  give  good  results  (Analyst  xiii.  185). 
They  use  a  -5^  solution  of  sodic  carbonate,  tinted  with  phenolph- 
thalein,  the  decolouration  of  which  by  formation  of  bicarbonate  is 
taken  as  the  end-reaction.  Figures  of  the  apparatus  required  and 


§26.  CARBONIC    ACID.  97 

details  are  given  in  the  Analyst,  being  a  translation  from  the 
original  paper  in  Zeitsclir.  f.  Ancjew.  Chein.,  1888.  I  have  serious 
doubts,  however,  whether  any  exact  method  can  be  obtained  with 
phenolphthalein  as  indicator,  where  the  CO2  is  being  absorbed. 
I  have  not  found  it  to  answer  in  the  case  of  CO2  in  coal  gas. 

Expired  Air. — Marcet  uses  a  special  vessel  for  the  treatment 
for  carbonic  acid  of  air  from  the  lungs  («/.  (7.  S.  1880,  495). 
The  absorption  by  baryta,  and  the.  analysis,  however,  do  not 
essentially  differ  from  the  method  described  above. 

6.     Scheibler's  Apparattis   for  the   estimation   of    Carbonic   Acid 

by  Volume. 

This  apparatus  is  adapted  for  the  estimation  of  the  CO2  contained 
in  native  carbonates,  as  well  as  in  artificial  products,  and  has  been 
specially  contrived  for  the  purpose  of  readily  estimating  the  CO2 
in  the  bone-black  used  in  sugar  refining.  The  principle  upon 
which  the  apparatus  is  founded  is  simply  this  : — That  the  quantity 
of  CO2  contained  in  calcic  carbonate  can  be  used  as  a  measure 
of  the  quantity  of  that  salt  itself ;  and  instead  of  determining,  as 
has  been  usually  the  case,  the  quantity  of  gas  by  weight,  this 
apparatus  admits  of  its  estimation  by  volume ;  and  it  is  by  this 
means  possible  to  perform,  in  a  few  minutes,  operations  which 
would  otherwise  take  hours  to  accomplish,  while,  moreover,  the 
operator  need  scarcely  possess  any  knowledge  of  chemistry.  The 
results  obtained  by  this  apparatus  are  correct  enough  for  technical 
purposes. 

The  apparatus  is  shown  in  fig.  28,  and  consists  of  the  following 
parts : — The  glass  vessel,  A,  serves  for  the  decomposition  of  the 
material  to  be  tested  for  CO2,  which  for  that  purpose  is  treated 
with  dilute  HC1 ;  this  acid  is  contained,  previous  to  the  experiment, 
in  the  gutta-percha  vessel  s.  The  glass  stopper  of  A  is  perforated, 
and  through  it  firmly  passes  a  glass  tube,  to  which  is  fastened  the 
india-rubber  tube  r,  by  means  of  which  communication  is  opened 
with  B,  a  bottle  having  three  openings  in  its  neck.  The  central 
opening  of  this  bottle  contains  a  glass  tube  (r)  firmly  fixed,  which 
is  in  communication,  on  the  one  hand,  with  A,  by  means  of  the 
flexible  india-rubber  tube  already  alluded  to,  and,  on  the  other 
hand,  inside  of  B,  with  a  very  thin  india-rubber  bladder,  K. 
The  neck  (q)  of  the  vessel  B  is  shut  off  during  the  experiment  by 
means  of  a  piece  of  india-rubber  tubing,  kept  firmly  closed  with  a 
spring  clamp.  The  only  use  of  this  opening  of  the  bottle  B, 
arranged  as  described,  is  to  give  access  of  atmospheric  air  to  the 
interior  of  the  bottle,  if  required.  The  other  opening  is  in 
communication  with  the  measuring  apparatus  C,  a  very  accurate 
cylindrical  glass  tube  of  150  c.c.  capacity,  divided  into  0'5  c.c. ; 
the  lower  portion  of  this  tube  C  is  in  communication  with  the 
tube  D,  serving  the  purpose  of  controlling  the  pressure  of  the  gas. 

H 


98 


VOLUMETRIC   ANALYSIS. 


26. 


The]  lower  part  of  this  tube  D  ends  in.  a  glass  tube  of  smaller 
diameter,  to  which  is  fastened  the  india-rubber  tube  p,  leading 
to  E,  but  the  communication  between  these  parts  of  the  apparatus 
is  closed,  as  seen  at  p,  by  means  of  a  spring  clamp.  E  is  a  water 
reservoir,  and  on  removal  of  the  clamp  at  p,  the  water  contained 


HUBERT  LV 


Tig.  28. 

in  C  and  D  runs  off  towards  E ;  when  it  is  desired  to  force  the 
water  contained  in  E  into  C  and  D,  this  can  be  readily  done 
by  blowing  with  the  mouth  into  V,  and  opening  the  clamp 
at  p. 

The  main  portion  of   the  apparatus  above  described,  with  the 


§26.  CARBONIC    ACID.  99 

exception,  however,  of  the  vessel  A,  is  fixed  by  means  of  brass 
fittings  to  a  wooden  board ;  a  thermometer  is  also  attached.  The 
filling  of  the  apparatus  with  water  is  very  readily  effected  by 
pouring  it  through  a  suitable  funnel  placed  in  the  open  end  of  the 
tube  D,  care  being  taken  to  remove,  or  at  least  to  unfasten,  the 
spring  clamp  at  p ;  in  this  manner  the  water  runs  into  E,  which 
should  be  almost  entirely  filled.  Distilled  water  is  preferable  for 
this  purpose,  especially  as  the  filling  only  requires  to  be  done  once, 
because  the  water  always  remains  in  E  as  long  as  the  apparatus  is 
intended  to  be  kept  ready  for  use.  When  it  is  required  to  fill  the 
tubes  C  and  D  with  water,  so  as  to  reach  the  zero  of  the  scale 
of  the  instrument,  it  is  best  to  remove  the  glass  stopper  from  A. 
The  spring  clamp  at  p  is  next  unfastened,  and  air  is  then  blown  by 
means  of  the  mouth  into  the  tube  V,  which  communicates  with  E ; 
by  this  operation  the  water  rises  up  into  the  tubes  C  and  D, 
which  thus  become  filled  with  that  liquid  to  the  same  height. 
Care  should  be  taken  not  to  force  the  water  up  above  the  zero 
of  the  scale  at  C,  and  especial  care  should  be  taken  against  forcing 
so  much  of  the  fluid  up  that  it  would  run  over  into  the  tube  u, 
and  thence  find  its  way  to  B,  whereby  a  total  disconnection  of 
all  the  parts  of  the  apparatus  would  become  necessary.  If  by  any 
accident  the  water  should  have  been  forced  up  above  the  zero  at  C, 
before  the  operator  had  closed  the  spring  clamp  at  p,  this  is  easily 
remedied  by  gently  opening  that  clamp,  whereby  room  is  given  for 
the  water  to  run  off  to  E  in  such  quantity  as  may  be  required  to 
adjust  the  level  of  that  fluid  in  C  precisely  with  the  zero  of  the  scale. 
The  filling  of  the  tube  C  with  water  has  the  effect  of  forcing  the  air 
previously  contained  in  that  tube  into  B,  where  it  causes  the 
compression  of  the  very  thin  india-rubber  ball  placed  within  B. 
If  it  should  happen  that  this  india-rubber  ball  has  not  become 
sufficiently  compressed  and  flattened,  it  is  necessary  to  unfasten  the 
spring  clamp  at  g,  and  to  cautiously  blow  air  into  B,  through 
the  tube  q,  by  which  operation  the  complete  exhaustion  of  the 
india-rubber  bladder  placed  within  B  is  readily  performed.  This 
operation  is  also  required  only  once,  because  during  the  subsequent 
experiments  the  india-rubber  bladder  K  is  emptied  spontaneously. 
It  may  happen,  however,  that  while  the  filling  of  the  tubes  D  and  C 
with  water  is  being  proceeded  with,  the  india-rubber  bladder  K 
has  become  fully  exhausted  of  air  before  the  water  in  C  reaches 
the  zero  of  the  scale.  In  that  case  the  level  of  the  water  in  the 
tubes  D  and  C  will  not  be  the  same,  but  will  be  higher  in  D : 
it  is  evident,  however,  that  this  slight  defect  can  be  at  once 
remedied  by  momentarily  unfastening  the  spring  clamp  at  q. 

The  apparatus  should  be  placed  so  as  to  be  out  of  reach  of  direct 
sunlight,  and  should  also  be  protected  against  the  heat  of  the 
operator's  body  by  intervention  of  a  glass  screen,  and  is  best  placed 
near  a  north  window,  so  as  to  afford  sufficient  light  for  reading  off 
the  height  of  the  water  in  the  tubes. 

H  2 


100  VOLUMETRIC   ANALYSIS.  §    26. 

In  testing  carbonates  the  method  is  as  follows  : — 

Put  the  very  finely  powdered  portion  of  carbonate  into  the  perfectly  dry 
decomposing  glass  A,  fill  the  gutta-percha  tube  with  10  c.c.  hydrochloric 
acid  of  1-12  sp.  gr.,  place  the  tube  cautiously  in  the  decomposing  glass,  and 
then  close  the  bottle  with  the  well-tallowed  stopper.  Here  the  water  will 
sink  a  little  in  C  and  rise  in  D ;  open  q  for  a  moment,  and  the  equilibrium 
will  be  restored.  Now  note  the  thermometer  and  barometer,  grasp  the  bottle 
with  the  right  hand  round  the  neck  to  avoid  warming,  raise  it,  incline  it 
slightly  so  that  the  hydrochloric  acid  may  mix  with  the  substance  gradually, 
and  at  the  same  time  with  the  left  hand  regulate  p,  so  that  the  water  in  the 
two  tubes  may  be  kept  at  exactly  the  same  height ;  continue  these  operations 
without  intermission,  till  the  level  of  the  water  in  C  does  not  change  for  a 
few  seconds.  Now  bring  the  columns  in  C  and  D  to  exactly  the  same  height., 
read  off  the  height  of  the  water,  and  note  whether  the  temperature  has 
remained  constant.  If  it  has,  the  number  of  c.c.  read  off  indicates  the 
liberated  CO2,  but  as  a  small  quantity  has  been  dissolved  by  the  hydrochloric 
acid,  it  is  necessary  to  make  a  correction.  Scheibler  has  determined  the 
small  amount  of  carbonic  acid  which  remains  dissolved  in  the  10  c.c. 
hydrochloric  acid  at  the  mean  temperature,  and  he  directs  to  add  0'8  c.c.  to 
the  volume  of  the  carbonic  acid  read  off.  Warington  (C.  N.  xxxi.  253) 
states  that  this  is  not  a  constant  quantity,  but  is  dependent  upon  the  volume 
of  gas  evolved,  and  this  ratio  he  fixes  at  7  per  cent,  of  the  gas  measured. 
Lastly,  the  volume  being  reduced  to  0°,  760  num.,  and  the  dry  condition,  the 
weight  is  found. 

Under  no  circumstances  can  the  method  be  considered  actually  accurate, 
but  for  technical  purposes  it  is  convenient,  as  the  operation  is  performed  in  a 
very  short  time,  and  is  specially  suitable  for  comparative  examinations  of 
various  specimens  of  the  same  material. 

If  it  is  desired  to  dispense  with  all  corrections,  each  set  of 
experiments  may  be  begun  by  establishing  the  relation  between 
the  CO2  obtained  in  the  process  (i.e.  the  CO2  actually  yielded 
+  0'S  c.c.)  and  pure  calcic  carbonate.  This  relation  is,  of  course, 
dependent  on  the  temperature  and  pressure  prevailing  on  the 
particular  day.  For  example,  from  0*2737  gm.  calcic  carbonate 
containing  0*1204  gm.  CO2,  63*8  c.c.  were  obtained,  including 
the  0*8  c.c. ;  and  in  an  analysis  of  dolomite  under  the  same 
circumstances  from  0'2371  gm.  substance,  57*3  c.c.  were  obtained, 
including  the  0'8  c.c. 

Therefore  63 "8  :  57 '3  :  :  0'1204  :  x,  or  a=0'1082,  consequently 
the  dolomite  contains  45'62  per  cent,  of  CO2. 

For  the  special  procedure  in  testing  bone-black,  used  in  sugar 
refining,  the  reader  is  referred  to  the  printed  instructions  supplied 
with  the  apparatus.* 

Wigner  (Analyst,  i.  158)  has  obtained  exceedingly  good  results 
in  the  analysis  of  lead  carbonates,  etc.,  with  Me  Leod's  gas 
apparatus.  The  nitrometer  has  also  been  turned  to  good  account 
for  the  same  purpose. 

*It  is  perhaps  almost  needless  to  say  that  the  modern  apparatus  designed  by 
Hempel,  Lunge,  and  others,  for  technical  gas  analysis,  practically  supersedes  that 
of  Scheihler.  The  methods  are  all, however, open  to  the  objection  that  an  uncertain 
portion  of  CO2  is  lost  by  aqueous  absorption. 


§    27.  COMBINED    ACIDS. ^   *       '  \\ '; '  >  ^;  ^  10L 

ESTIMATION    OP    COMBINED    ACIDS   IN    NEUTRAL    SALTS. 

§  27.  THIS  comprehensive  method  of  determining  the  quantity 
of  acid  in  neutral  compounds  (but  not  the  nature  of  the  acid),  is 
applicable  only  in  those  cases  where  the  base  is  perfectly  precipitated 
by  an  excess  of  caustic  alkali  or  its  carbonate.  The  number  of 
bodies  capable  of  being  so  precipitated  is  very  large,  as  has  been 
proved  by  the  researches  of  Langer  and  Wawnikiewicz  (Ann. 
Chem.  u.  Phar.  1861,  239),  who  seem  to  have  worked  out  the 
method  very  carefully.  These  gentlemen  attribute  its  origin  to 
Buns  en;  but  it  does  not  seem  certain  who  devised  it.  The  best 
method  of  procedure  is  as  follows  : — 

The  substance  is  weighed,  dissolved  in  water  in  a  300-c.c.  flask,  heated  to 
boiling  or  not,  as  may  be  desirable ;  normal  alkali  or  its  carbonate,  according 
to  the  nature  of  the  base,  is  then  added  from  a  burette,  until  the  whole  is 
decidedly  alkaline.  It  is  then  diluted  to  300  c.c.  and  put  aside  to  settle,  and 
100  c.c.  are  taken  out  and  titrated  for  the  excess  of  alkali ;  the  remainder 
multiplied  by  3,  gives  the  measure  of  the  acid  combined  with  the  original 
salt,  i.e.  supposing  the  precipitation  is  complete. 

Example  :  2  gm.  crystals  of  baric  chloride  were  dissolved  in  water,  heated 
to  boiling,  and  20  c.c.  normal  sodic  carbonate  added,  diluted  to  300  c.c.  and 
100  c.c.  of  the  clear  liquid  titrated  with  normal  nitric  acid,  of  which  1'2  c.c. 
were  required :  altogether,  therefore,  the  2  gm.  required  16"4  c.c.  normal 
alkali ;  this  multiplied  by  0'122  gave  2'0008  gm.  Bad2  2H20  instead  of 
2  gm. ;  multiplied  by  the  factor  for  chlorine  0'03537,  it  yielded  0'58007  gm. 
Theory  requires  0'5809  gm.  chlorine. 

The  following  substances  have  been  submitted  to  this  mode  of 
examination  with  satisfactory  results  : — 

Salts  of  the  alkaline  earths  precipitated  with  an  alkaline 
carbonate  while  boiling  hot. 

Salts  of  magnesia,  with  pure  or  carbonated  alkali. 

Alum,  with  carbonate  of  alkali. 

Zinc  salts,  boiling  hot,  with  the  same. 

Copper  salts,  boiling  hot,  with  pure  potash. 

vSilver  salts,  with  same. 

Bismuth  salts,  half  an  hour's  boiling,  with  sodic  carbonate. 

Mckel  and  cobalt  salts,  with  the  same. 

Lead  salts,  with  the  same. 

Iron  salts,  boiling  hot,  with  pure  or  carbonated  alkali. 

Mercury  salts,  with  pure  alkali. 

Protosalts  of  manganese,  boiling  hot,  with  sodic  carbonate. 

Chromium  persalts,  boiling  hot,  with  pure  potash. 

Where  the  compound  under  examination  contains  but  one  base 
precipitable  by  alkali,  the  determination  of  the  acid  gives,  of 
course,  the  quantity  of  base  also. 

Wolcott  Gibbs  (C.  N.  1868,  i.  151)  has  enunciated  a  new 
acidimetric  principle  applicable  in  cases  where  a  base  is  precipitable 
at  a  boiling  temperature  by  hydric  sulphide,  and  the  acid  set  free 
so  as  to  be  estimated  with  standard  alkali.  Of  course  the  method 


102  ;  ;      ;VpLtMETEIC   ANALYSIS.  §    28. 

can  only  be  used  where  complete  separation  can  be  obtained,  and 
where  the  salt  to  be  analyzed  contains  a  fixed  acid  which  has  no 
effect  upon  hydric  sulphide.  A  weighed  portion  is  dissolved  in 
water,  brought  to  boiling,  and  the  gas  passed  in  until  the  metal  is 
completely  precipitated ;  which  is  known  by  testing  a  drop  of  the 
clear  liquid  upon  a  porcelain  tile  with  sulphuretted  hydrogen 
water,  or  any  other  appropriate  agent  adapted  to  the  metallic  salt 
under  examination. 

The  liquid  is  filtered  from  the  precipitate,  and  the  latter  well 
washed,  and  the  solution  made  up  to  a  definite  measure.  An 
aliquot  portion  is  then  titrated  with  normal  alkali  as  usual,  with 
one  of  the  phenol  indicators. 

In  the  case  of  nitrates  or  chlorides,  where  nitric  or  hydrochloric 
acid  would  interfere  with  the  hydric  sulphide,  it  was  found  that  the 
addition  in  tolerable  quantity  of  a  neutral  salt  containing  an  organic 
acid  (e.cj.  sodic  or  potassic  tartrate,  or  the  double  salt)  obviated  all 
difficulty. 

The  results  obtained  by  Gibbs  in  the  case  of  copper,  lead, 
bismuth,  and  mercury,  as  sulphate,  nitrate,  and  chloride,  agreed 
very  closely  with  theory;  but  the  process  would  be  very  objectionable 
to  many,  on  account  of  the  offensive  and  poisonous  character  of 
the  gas  necessarily  employed  in  the  precipitation. 

EXTENSION  OF  ALKALIMETBJC  METHODS. 

§  28.  BOHLIG  (Z.  a.  C.  1870,  310)  has  described  a  method 
for  the  estimation  of  sulphuric  acid,  baryta,  chlorine,  iodine,  and 
bromine,  which  appears  worthy  of  some  consideration,  since  the 
only  standard  solutions  required  are  an  acid  and  an  alkali. 

Alkaline  sulphates  are  known  to  be  partially  decomposed,  in 
contact  with  baric  carbonate,  into  alkaline  carbonates  and  baric 
sulphate.  The  decomposition  is  complete  in  the  presence  of  free 
carbonic  anhydride ;  acid  carbonates  of  the  alkali-metals  are  left  in 
solution,  together  with  some  acid  baric  carbonate,  which  can  be 
removed  by  boiling.  The  solution  is  filtered,  and  the  alkaline 
carbonate  determined  by  means  of  a  standard  acid  solution,  and 
the  amount  of  sulphuric  acid  or  alkaline  sulphate  calculated 
from  the  amount  of  normal  acid  required.  This  process  has  been 
satisfactorily  used  by  Haubst  for  sulphates  in  waters  (C.  N. 
xxxvi.  227),  and  by  Grossman  for  salt  cake  (C.  N.  xli.  114). 
See  also  §  16.15. 

Neutral  chlorides,  bromides,  and  iodides,  more  especially  of  the 
alkali-metals,  are  most  readily  decomposed  by  pure  silver  oxide 
into  insoluble  silver  salts,  leaving  the  alkali-metal  in  solution  as 
hydrate  (ammonia  salts  always  excepted),  which  can  then  be 
determined  as  usual  by  standard  acid. 

The  author  treats  solutions  containing  sulphates  of  the  heavy 
metals,  of  the  earths  or  alkaline  earths,  and  free  from  acids  whose 


§    28.  ALKALIMETKIC    METHODS.  103 

presence  would  influence  the  method,  viz.,  phosphoric,  arsenic, 
oxalic,  etc.,  with  a  solution  of  potassic  carbonate,  so  as  to  precipitate 
the  bases  and  leave  about  double  or  treble  the  amount  of  alkaline 
carbonate  in  solution.  From  1  to  1J  gin.  of  substance  is  operated 
upon  in  a  flask.  The  solution  is  made  up  to  500  c.c.,  well  shaken, 
and  the  precipitate  allowed  to  subside.  50  c.c.  are  then  filtered, 
and  titrated  with  standard  acid  and  methyl  orange.  Another  100  c.c. 
are  filtered  in  like  manner  into  a  strong  quarter-liter  flask,  and 
diluted  with  about  100  c.c.  of  hot  water;  the  requisite  quantity  of 
normal  acid  is  then  run  in  at  once  from  a  burette ;  the  solution 
diluted  to  250  c.c. ;  and  about  a  gram  of  dry  baric  carbonate 
(free  from  alkali)  added.  The  flask  is  next  closed,  and  the  liquid 
well  agitated.  The  decomposition  of  the  alkaline  sulphate  is 
complete  in  a  few  minutes.  The  flask  should  be  opened  now  and 
then  to  allow  the  carbonic  anhydride  to  escape.  Finally,  about 
J  gm.  of  pulverized  baric  hydrate  is  added,  the  whole  well  shaken, 
and  a  portion  of  the  rapidly  clearing  liquid  tested  qualitatively  for 
barium  and  sulphuric  acid.  The  result  should  be  a  negative  one. 
50  c.c.,  corresponding  to  20  c.c.  of  the  original  solution,  are  then 
filtered  and  titrated  with  normal  acid,  and  the  quantity  of  sulphuric 
acid  (sulphate)  calculated  as  usual. 

The  source  of  carbonic  anhydride  is  thus  placed  in  the  liquid 
itself,  provided  the  quantity  of  potassic  carbonate  be  not  too  small. 

Equivalent  quantities  of  K2SO  +  2K2C03  +  2HC1  +  BaCO3  when 
mixed  with  sufficient  water  change  into  BaSO4  +  2KHC03  +  2KC1, 
and  it  is  therefore  more  than  sufficient  to  add  twice  the  quantity 
of  potassic  carbonate  compared  with  the  alkaline  sulphate  operated 
upon. 

Baric  hydrate  is  added  with  a  view  of  removing  any  carbonic 
anhydride  left  in  the  liquid  after  boiling,  which  would  otherwise 
dissolve  some  of  the  excess  of  baric  carbonate  contained  in  the 
precipitate. 

Any  baric  hydrate  not  required  to  remove  CO2  is  acted  upon  by 
the  acid  potassic  carbonate,  but  does  not  influence  the  final  result. 

Phosphoric  and  oxalic  acids  the  author  proposes  to  remove  by 
means  of  calcic  chloride;  chromic  acid  by  deoxidizing  agents, 
such  as  alcohol  and  hydrochloric  acid.  Bohlig  recommends  this 
method  for  estimating  sulphuric  acid  in  ashes,  crude  soda,  Stassfurth 
salts,  etc. 

Solutions  containing  baryta  are  estimated  in  like  manner  by 
precipitation  as  carbonate,  and  decomposition  with  potassic  sulphate 
in  a  solution  containing  free  carbonic  acid.  Chlorine  is  determined 
in  solutions  by  first  precipitating  any  metallic  chloride  with  potassic 
carbonate  added  in  moderate  excess.  The  filtrate  is  made  up  to 
250  c.c.,  and  the  excess  of  potassic  carbonate  determined  in  50  c.c. 
by  means  of  a  normal  solution  of  HC1.  125  c.c.  of  the  solution 
are  next  treated  with  excess  of  silver  oxide  and  made  up  to  250  c.c., 
well  shaken  (out  of  contact  with  the  light)  and  filtered.  100  c.c. 


104  VOLUMETKIC  ANALYSIS.  §    28. 

of  the  filtrate  are  titrated  with  normal  hydrochloric  acid.  The 
difference  between  the  quantity  of  acid  required  in  the  last  and 
that  of  the  first  experiment,  multiplied  by  5,  gives  the  amount  of 
chlorine  contained  in  the  original  solution.  A  portion  of  the 
filtrate  should  be  tested  for  chlorine  by  means  of  mercurous  nitrate. 

The  filtrate  is  obtained  perfectly  clear  only  in  the  presence  of 
some  potassic  or  sodic  carbonate,  and  by  employing  argentic  oxide 
free  from  argentous  oxide.  A  few  drops  of  pure  potassic  per- 
manganate added  to  the  argentic  oxide  preserved  in  water  prevent 
formation  of  the  latter.  The  oxide  to  be  employed  for  each 
experiment  is  filtered  when  required,  and  thoroughly  washed. 

Bromine  and  iodine  are  determined  in  like  manner.  The  author 
has  not  been  able,  however,  to  estimate  the  mixtures  of  the  halogen 
salts ;  but  he  has  made  the  interesting  observation  that  potassic 
iodide,  when  boiled  with  potassic  permanganate,  is  completely 
oxidized  into  iodate.  This  facilitates  the  detection  of  small 
quantities  of  chlorine  and  bromine,  in  the  presence  of  much 
iodide.  The  greater  part  of  iodate  may  be  separated  also  by 
precipitation  with  baric  nitrate  before  determining  chlorine.  The 
standard  acid  solutions  which  Bohlig  employed  contained  not  more 
than  one-third  of  the  equivalent  of  HC1  or  SO3  per  liter. 

For  further  particulars  the  reader  is  referred  to  the  original 
paper  (Arch.  Pharm.  3  cxlv.  113). 

Siebold  (Year  Book  of  Pharmacy,  1878,  518)  describes  a  very 
ingenious  process,  devised  by  himself,  for  the  titration  of  caustic 
and  carbonated  alkalies  by  means  of  prussic  acid,  the  principle  of 
which  is  explained  in  §  55.  The  process  is  useful  in  the  case  of 
carbonates,  since  CO2  is  no  hindrance. 

0'5  to  1  gm.  of  the  alkali  or  alkaline  carbonate  is  dissolved  in  about  100  c.c. 
of  water,  and  an  excess  of  hydrocyanic  acid  (say  10  or  20  c.c.)  of  5  per  cent, 
solution  added;  then  ^  silver  solution  cautiously  added  with  constant 
stirring  until  a  faint  permanent  turbidity  occurs.  Each  c.c.  of  ^  silver 
^0-0138  gm.  K2CO3,  or  0'0106  gm.  Na2CO3. 

In  the  case  of  chlorides  being  present,  their  quantity  may  be 
determined  by  boiling  down  the  mixture  to  about  half  its  volume 
to  expel  all  free  prussic  acid,  adding  a  drop  or  two  of  potassic 
chromate  as  indicator,  then  titrating  with  —$  silver.  Any  excess 
above  that  required  in  the  first  titration  will  be  due  to  chlorine, 
and  may  be  calculated  accordingly. 


29.  OXIDATION    AND    REDUCTION    ANALYSES.  105 


PART    III. 
AXALYSIS    BY    OXIDATION    OR    REDUCTION 

§  29.  THE  series  of  analyses  wliicli  occur  under  this  system  are 
very  extensive  in  number,  and  not  a  few  of  them  possess  extreme 
accuracy,  such  in  fact,  as  is  not  possible  in  any  analysis  by  weight. 
The  completion  of  the  various  processes  is  generally  shown  by  a 
distinct  change  of  colour ;  such,  for  instance,  as  the  occurrence  of 
the  beautiful  rose-red  permanganate,  or  the  blue  iodide  of  starch ; 
and  as  the  smallest  quantity  of  these  substances  will  colour 
distinctly  large  masses  of  liquid,  the  slightest  excess  of  the  oxidizing 
agent  is  sufficient  to  produce  a  distinct  effect. 

The  principle  involved  in  the  process  is  extremely  simple. 
Substances  which  will  take  up  oxygen  are  brought  into  solution, 
and  titrated  with  a  substance  of  known  oxidizing  power ;  as,  for 
instance,  in  the  determination  of  ferrous  salts  by  permanganic 
acid.  The  iron  is  ready  and  willing  to  receive  the  oxygen, 
the  permanganate  is  equally  willing  to  part  with  it ;  while  the  iron 
is  absorbing  the  oxygen,  the  permanganate  loses  its  colour  almost 
as  soon  as  it  is  added,  and  the  whole  mixture  is  colourless ;  but 
immediately  the  iron  is  satisfied,  the  rose  colour  no  longer  disappears, 
there  being  no  more  oxidizable  iron  present.  In  the  case  of  potassic 
permanganate  the  reaction  is:  10FeO  +  2MnK04  =  5Fe203  + 
2MnO  +  K20.  Oxalic  acid  occupies  the  same  position  as  the 
ferrous  salts  ;  its  composition  is  C204H2  +  2H20  =  126.  If  perman- 
ganate is  added  to  it  in  acid  solution,  the  oxalic  acid  is  oxidized  to 
carbonic  acid,  and  the  manganic  reduced  to  manganous  oxide,  thus 
Mn207  +  5C204H2  +  2H2S04  =  10C02  +  2MnS04  +  7H20.  When 
the  oxalic  acid  is  all  decomposed,  the  colour  of  the  permanganate 
no  longer  disappears.  On  the  other  hand,  substances  which  will 
give  up  oxygen  are  deoxidized  by  a  known  excessive  quantity  of 
reducing  agent,  the  amount  of  which  excess  is  afterwards  ascertained 
by  residual  titration  with  a  standard  oxidizing  solution;  the  strength 
of  the  reducing  solution  being  known,  the  quantity  required  is  a 
measure  of  the  substance  which  has  been  reduced  by  it. 

The  oxidizing  agents  best  available  are — potassic  permanganate, 
iodine,  potassic  bichromate,  and  red  potassic  prussiate. 

The  reducing  agents  are — sulphurous  acid,  sodic  hyposulphite,* 
sodic  thiosulphate,  oxalic  acid,  ferrous  oxide,  arsenious  anhydride, 
stannous  chloride,  yellow  potassic  prussiate,  and  zinc  or  magnesium. 

With  this  variety  of  materials  a  great  many  combinations  may  be 
arranged  so  as  to  make  this  system  of  analysis  very  comprehensive ; 

*  Schiitzenberger's  preparation  is  here  meant. 


106  VOLUMETRIC  ANALYSIS.  §    30. 

but  the  following  are  given  as  sufficient  for  almost  all  purposes, 
and  as  being  susceptible  of  the  greatest  amount  of  purity  and 
stability  of  material,  with  exceedingly  accurate  results  : — 

1.  Permanganate  and    ferrous  salts  (with  the  rose   colour  as 
indicator);    permanganate  and  oxalic   acid  (with  the  rose  colour 
as  indicator). 

2.  Potassic  bichromate  and  ferrous  salts  (with  cessation  of  blue 
colour  when   brought   in  contact  with   red  potassic  prussiate,  as 
indicator). 

3.  Iodine  and  sodic  thiosulphate  (with   starch  as  indicator) ; 
iodine  and  sodic  arsenite  (with  starch  as  indicator.) 


PREPARATION     OF    STANDARD     SOLUTIONS. 

PERMANGANIC    ACID    AND    FERROUS    OXIDE. 

1.     Potassic   Permanganate. 
Mn2K2Os  =  315-6.     Decinormal  Solution  =  3-156  gin.  per  liter. 

§  30.  THE  solution  of  this  salt  is  best  prepared  for  analysis  by 
dissolving  the  pure  crystals  in  fresh  distilled  water,  and  should  be 
of  such  a  strength  that  17 '85  c.c.  will  oxidize  1  decigram  of  iron. 
The  solution  is  then  decinormal.  If  the  salt  can  be  had  perfectly 
pure  and  dry,  3 '156  gm.  dissolved  in  a  liter  of  water  at  16°  C.  will 
give  an  exactly  decinormal  solution ;  but,  nevertheless,  it  is  always 
well  to  verify  it  as  described  below.  If  well  kept,  it  will  retain  its 
strength  for  several  weeks,  but  should  from  time  to  time  be 
verified  by  titration  in  one  of  the  following  ways  : — 

2.      Titration    of   Permanganate. 

(a)  With  Metallic  Iron. — The  purest  iron  to  be  obtained  is 
thiii  annealed   binding-wire    free    from  rust,  generally  known  as 
flower  wire. 

About  O'l  gm.  of  wire  is  dissolved  in  dilute  pure  sulphuric  acid,  by  the 
aid  of  heat,  in  a  small  flask  closed  with  a  cork,  through  which  a  fine  glass  tube 
is  passed,  so  that  the  hydrogen  which  is  evolved  escapes  under  slight  pressure, 
thus  preventing  the  access  of  air;  or  the  apparatus  shown  in  §  59  may  be 
used.  When  the  iron  is  all  dissolved  the  flask  may  be  two-thirds  filled  with 
cold,  recently  boiled,  distilled  water,  and  the  titration  with  permanganate 
commenced  and  concluded  as  in  the  case  of  the  double  sulphate. 

The  decomposition  which  ensues  from  titrating  ferrous  oxide  by 
permanganic  acid  may  be  represented  as  follows  : — 

lOFeO  and  Mn207  =  2MnO  and  5Fe203' 

(b)  With  Ammonio-ferrous  Sulphate. — In    order    to    ascertain 
the    strength    of  *  the    permanganate,    it   may  be    titrated  with  a 
weighed  quantity  of  this  substance  instead  of  metallic  iron. 


§    30.  VERIFICATION    OF    PERMANGANATE.  107 

This  salt  is  a  convenient  one  for  titrating  the  permanganate,  as  it  saves  the 
time  and  trouble  of  dissolving  the  iron,  and  when  perfectly  pure,  it  can  be 
depended  on  without  risk.  To  prepare  it,  139  parts  of  the  purest  crystals  of 
ferrous  sulphate,  and  66  parts  of  pure  crystallized  ammonic  sulphate  are 
separately  dissolved  in  the  least  possible  quantity  of  distilled  water  of  about 
40°  C.  (if  the  solutions  are  not  perfectly  clear  they  must  be  filtered) ;  mix 
them  at  the  same  temperature  in  a  porcelain  dish,  adding  a  few  drops  of 
pure  sulphuric  acid,  and  stir  till  cold.  During  the  stirring  the  double  salt 
will  fall  in  a  finely  granulated  form.  Set  aside  for  a  few  hours,  then  pour 
off  the  supernatant  liquor,  and  empty  the  salt  into  a  clean  funnel  with  a  little 
cotton  wool  stuffed  into  the  neck,  so  that  the  mother-liquor  may  drain  away ; 
the  salt  may  then  be  quickly  and  repeatedly  pressed  between  fresh  sheets  of 
clean  filtering  paper.  Lastly,  place  in  a  current  of  air  to  dry  thoroughly, 
so  that  the  small  grains  adhere  no  longer  to  each  other,  or  to  the  paper  in 
which  they  are  contained,  then  preserve  in  a  stoppered  bottle  for  use. 

The  formula  of  the  salt  is— Fe  (^TH4)2  (SO4)2,  6H20  =  392. 
Consequently  it  contains  exactly  one-seventh  of  its  weight  of  iron ; 
therefore  0*7  gm.  represents  O'l  gm.  Ee,  and  this  is  a  convenient 
quantity  to  weigh  for  the  purpose  of  titrating  the  permanganate. 

0'7  gm.  being  brought  into  dilute  solution  in  a  flask  or  beaker,  and  5  or 
6  c.c.  of  dilute  sulphuric  acid  (1  to  5)  added  (the  titration  of  permanganate, 
or  any  other  substance  by  it,  should  always  take  place  in  the  presence  of  free 
acid,  and  preferably  sulphuric),  the  permanganate  is  delivered  from  a  burette 
with  glass  tap  divided  in  i-  or  TV  c.c.,  until  a  point  occurs  when  the  rose 
colour  no  longer  disappears  on  shaking.  A  drop  or  two  of  the  permanganate 
in  excess  suffices  to  produce  this  effect.  The  titration  is  now  ended,  and 
should  the  quantity  not  be  strictly  correct,  the  number  of  c.c.  used  may  be 
marked  upon  the  bottle  as  the  quantity  for  O'l  gm.  Pe,  or  the  factor  found, 
which  is  necessary  to  reduce  it  to  decinormal  strength,  or  if  too  strong,  it 
may  be  diluted  to  that  strength  at  once. 

(c)  With  Oxalic  Acid. — This  is  perhaps  the  least  recommendable  of  the 
methods  of    titrating  permanganate,  owing  to  the  difficulty  of    preparing 
oxalic  acid  of  definite  hydration.     0'63  gm.  of  the  pure  acid  is  to  be  weighed, 
or  10  c.c.  of  normal  solution  measured  with  a  pipette,  brought  into  a  flask 
with  dilute  sulphuric  acid,  as  in  the  case  of  the  iron  salt,  and  considerably 
diluted  with  water,  then  warmed  to  about  60°  C.,  and  the  permanganate 
added  from  the  burette.     The  colour  disappears  slowly  at  first,  but  after- 
wards more   rapidly,   becoming    first   brown,   then   yellow,  and   so   on   to 
colourless.    More  care  must  be  exercised  in  this  case  than  in  the  titration 
with  iron,  as  the  action  is  less  decisive  and  rapid. 

(d)  With  Lead  pxalate. — S  t  o  1  b  a  prefers  this  salt  to  oxalic  acid,  for  the 
reasons  that  it  contains  no  water,  is  not  liable  to  absorb  any  from  exposure, 
and  has  a  high  molecular  weight,  1  part  of  the  salt  representing  0'42799  of 
oxalic  acid,  or  63  oxalic  acid  =  147'2  lead  oxalate. 

The  method  of  titration  is  similar  to  that  with  oxalic  acid,  using  dilute 
sulphuric  acid,  and  warming  the  mixture  to  insure  the  complete  decomposi- 
tion of  the  salt  into  lead  sulphate  and  free  oxalic  acid.  Sodic  oxalate  is 
also  anhydrous  and  equally  serviceable. 

The  lead  oxalate  is  prepared  by  precipitating  pure  lead  acetate  with  oxalic 
acid  in  excess,  and  washing  the  precipitate  by  decantation  with  warm  water 
till  all  free  acid  is  removed ;  the  precipitate  is  then  dried  at  120°  C.,  and 
preserved  for  use.  Some  operators  prefer  to  use  ammonic  oxalate  in  place  of 
oxalic  acid  or  lead  oxalate,  as  being  a  substance  of  definite  hydration,  and 
easily  obtained  in  a  pure  state.  Its  formula  is  (NH4)2  C2O4,  H2O=142= 
2Fe.  The  titration  is  carried  on  precisely  as  in  the  case  of  oxalic  acid. 


108  VOLUMETRIC   ANALYSIS.  §    30. 

(e)  "With  Hydrogen  Peroxide  in  the  Nitrometer. — 111  a  paper 
011  this  subject  by  Lunge  (/.  S.  C.  I.  ix.  21),  it  is  shown  by 
very  carefully  conducted  experiments  with  purest  materials 
and  verified  apparatus  that  exceedingly  accurate  results  may  be 
obtained  by  the  modified  nitrometer  with  patent  tap  (illustrated 
at  the  end  of  Part  VII.).  Lunge's  experiments  were  made 
on  a  semi-normal  solution  of  permanganate  (1  c.c.  =  0*004  gin.  0), 
but  whether  equally  exact  results  would  be  obtained  with  —^ 
permanganate  I  cannot  say,  not  having  tried  it ;  but  of  course  an 
approximately  semi-normal  solution  may  be  made  and  reduced  to 
either  f  or  ~  strength,  if  desired,  by  dilution  with  fresh  distilled 
water.  The  exact  method  of  using  this  new  gas  volumeter  will  be 
described  under  the  head  of  Nitrometer  in  Part  VII.  ;  but  so  far 
as  permanganate  is  concerned  it  wras  found  that  convenient 
quantities  of  substances  to  use  were  10  c.c.  of  f  permanganate, 
15  c.c.  of  ordinary  10  volume  H202,  and  30  c.c.  of  sulphuric  acid 
1  :  5.  The  nitrometer  having  been  charged  with  water,  the 
mixture  was  shaken  up  and  allowed  to  stand  ten  minutes,  shaken 
again  and  read  off  after  five  minutes.  The  volume  of  oxygen 
so  obtained  was  corrected  for  temperature  and  pressure,  then 
calculated  into  weight.  The  results  of  three  experiments  using 
the  quantities  mentioned  above  were  as  follows : — 

1.  Corrected  volume  of  O  55'92  c.c. =0*004007  gm. 

2.  „  „  „     55*82  c.c.  =  0-004000    „ 

3.  „  „  „     55'82  c.c.  =  0*004000   „ 
Average  0'004002  gm.  of  oxygen  per  c.c.  of  solution. 

Three  experiments  with  the  same  permanganate  solution  gave, 
when  iron  wire  was  used,  an  average  of  0-00399  gm.,  and  with 
oxalic  acid  0 '003997  gm.  of  oxygen  respectively  per  c.c. 

As  Lunge  says:  "We  cannot  but  infer  that  standardizing 
a  solution  of  permanganate  with  hydrogen  peroxide  in  the 
nitrometer  when  observing  the  prescribed  precautions  is  one  of 
the  most  accurate  known  methods  for  this  purpose,  and  withal 
possesses  the  great  advantage  that  it  is  carried  out  within  an 
extremely  short  time,  without  requiring  a  fundamental  substance 
of  accurately  known  composition." 

Many  other  substances  have  been  proposed  for  standardizing 
permanganate,  such  as  potassic  ferrocyanide,  thiocyanate,  vanadic 
oxide,  etc.,  but  they  are  all  inferior  in  value  to  those  above  named. 

3.      Precautions    in    Titrating-    with    Permanganate. 

It  must  be  borne  in  mind  that  free  acid  is  always  necessary  in 
titrating  a  substance  with  permanganate,  in  order  to  keep  the 
resulting  manganous  oxide  in  solution.  Sulphuric  acid,  in  a  dilute 
form,  has  no  prejudicial  effect  on  the  pure  permanganate,  even  at  a 
high  temperature.  With  hydrochloric  acid  the  solution  to  be 
titrated  must  be  very  dilute  arid  of  low  temperature,  otherwise 
chlorine  will  be  liberated  and  the  analysis  spoiled.  This  acid  acts 


§    31.  FACTORS    FOE    PERMANGANATE.  109 


as  a  reducing 
thus — 


ig    agent   on  permanganate    in  concentrated    solution, 

Mii20T  +  14HC1  =  7H20  +  10C1  +  2MnCR 
The  irregularities  due  to  this  reaction  may  be  entirely  obviated 
by  the  addition  of  a  few  grains  of  manganous  or  magnesic  sulphate 
before  titration. 

Organic  matter  of  any  kind  decomposes  the  permanganate,  and 
the  solution  therefore  cannot  be  filtered  through  paper,  nor  can  it 
be  used  in  Mohr's  burette,  because  it  is  decomposed  by  the 
india-rubber  tube.  It  may,  however,  be  filtered  through  gun  cotton 
or  glass  wool. 

TITRATION    OF    FERRIC    SALTS    BY    PERMANGANATE. 

§  31.  ALL  ferric  compounds  requiring  to  be  estimated  by 
permanganate  must,  of  course,  be  reduced  to  the  ferrous  state. 
This  is  best  accomplished  by  metallic  zinc  or  magnesium  in  sulphuric 
acid  solution.  Hydrochloric  may  also  be  used  with  the  precautions 
mentioned. 

The  reduction  occurs  on  simply  adding  to  the  warm  diluted 
solution  small  pieces  of  zinc  (free  from  iron,  or  at  least  with  a 
known  quantity  present)  or  coarsely  powdered  magnesium  until 
colourless  ;  or  until  a  drop  of  the  solution  brought  in  contact  with 
a  drop  of  potassic  sulphocyanide  produces  no  red  colour.  All  the 
zinc  or  magnesium  must  be  dissolved  previous  to  the  titration. 

The  reduction  may  be  hastened  considerably  as  shown  in  §  59.3. 

When  the  reduction  is  complete,  no  time  should  be  lost  in 
titrating  the  solution. 

CALCULATION    OF    ANALYSES    MADE    WITH 
PERMANGANATE     SOLUTION. 

§  32.  THE  calculation  of  analyses  with  permanganate,  if  the 
solution  is  not  strictly  decinormal,  can  be  made  by  ascertaining  its 
factor,  reducing  the  number  of  c.c.  used  for  it  to  decinormal 
strength,  and  multiplying  the  number  of  c.c.  thus  found  by  ^-Q^Q-g- 
of  the  equivalent  weight  of  the  substance  sought ;  for  instance — 

Suppose  that  15  c.c.  of  permanganate  solution  have  been  found 
to  equal  O'l  gm.  iron;  it  is  required  to  reduce  the  15  c.c. 
to  decinormal  strength,  which  would  require  1000  c.c.  of  per- 
manganate to  every  5 '6  gm.  iron,  therefore  5 '6  :  1000  :  :  O'l  :  x  = 
17-85  c.c. ;  17-85  x  0-0056  =  0-09996  gm.  iron,  which  is  as  near  to 
O'l  gin.  as  can  be  required.  Or  the  factor  necessary  to  reduce 
the  number  of  c.c.  used  may  be  found  as  follows: — O'l  :  15  :  : 

5'6  :  5c  =  84  c.c.,  therefore  -~-;-  =  l'19.     Consequently  1*19  is  the 

factor  by  which  to  reduce  the  number  of  c.c.  of  that  special 
permanganate  used  in  any  analysis  to  the  decinormal  strength,  from 
whence  the  weight  of  substance  sought  may  be  found  in  the 
usual  way. 


110 


VOLUMETRIC   ANALYSIS. 


32. 


Another  plan  is  to  find  the  quantity  of  iron  or  oxalic  acid  repre- 
sented by  the  permanganate  used  in  any  given  analysis,  and  this  being 
done  the  following  simple  equation*  gives  the  required  result  :  — 

Fe  (56)  eq.  weight  of  .         the  weight  the  weight  of 

or         :      the  substance     :  :    of  Fe  or        :         substance 

0  (63)  sought  0  found  sought 

In  other  words,  if  the  equivalent  weight  of  the  substance  analyzed 
be  divided  by  56  or  63  (the  respective  equivalent  weights  of  iron  or 
oxalic  acid),  a  factor  is  obtained  by  which  to  multiply  the  weight 
of  iron  or  oxalic  acid,  equal  to  the  permanganate  used,  and  the 
product  is  the  weight  of  the  substance  analyzed. 

For  example  :  sulphuretted  hydrogen  is  the  substance  sought, 
the  eq.  weight  of  H2S  corresponding  to  2  eq.  Fe  is  17  ;  let  this 

number  therefore  be  divided  by  56,  gg  =  0'3036,  therefore,  if  the 

quantity  of  iron  represented  by  the  permanganate  used  in  an 
estimation  of  H2S  be  multiplied  by  0'3036,  the  product  will  be 
the  weight  of  the  sulphuretted  hydrogen  sought. 

Again  :  in  the  case  of  manganic  peroxide  whose  equivalent 
weight  is  43*4. 

43-4     ._ 


The  weight  of  iron  therefore  found  by  permanganate  in  any  analysis 
multiplied  by  the  factor  0'775  will  give  the  amount  of  manganic 
peroxide,  MnO2.  Again:  if  m  gm.  iron  =  It  c.c.  permanganate, 

then  1  c.c.  permanganate  =  -7;  gm.  metallic  iron. 

The  equivalents  here  given  are  on  the  hydrogen  scale,,  in 
accordance  with  the  normal  system  of  solutions  adopted  ;  and  thus 
it  is  seen  that  two  equivalents  of  iron  are  converted  from  the 
ferrous  to  the  ferric  state  by  the  same  quantity  of  oxygen  as 
suffices  to  oxidize  one  equivalent  of  oxalic  acid,  sulphuretted 
hydrogen,  or  manganic  peroxide. 

1  c.c.  decinormal  permanganate  is  equivalent  to 


0*0056    gm.  Fe  estimated  in  the  ferrous  state 

0-0072       , 

FeO 

0-008 

Fe203 

0-003733 

Fe 

,'      froinFeS 

0-0059 

Sn 

5 

,     SnCl2 

0-00295 

Sn 

3 

,     SnS2 

0-00315 

Cu 

,     CuS 

0-00274 

Mn 

\ 

,     MnS 

0-00315 

Cu 

,     Cu+Fe2Cl6 

0-0063 

Cu 

t 

CuO+Fe 

0-0017 

H2S 

)           ?> 

0-0008 

O 

0-OOF3 

0 

0-002 

Ca  from  CaC2O4 

0-0120 

Ur     „     UrO,  etc.,  etc. 

§    33.  BICHROMATE    ANALYSES.  Ill 

When  possible  the  necessary  factors  will  be  given  in  the  tables 
preceding  any  leading  substance. 


CHROMIC    ACID    AND    FERROUS    OXIDE. 

§  33.  POTASSIC  bichromate,  which  appears  to  have  been  first 
proposed  by  Penny,  possesses  the  advantage  over  permanganate, 
that  it  is  absolutely  permanent  in  solution,  may  easily  be  obtained 
in  a  pure  state,  and  its  solution  may  be  used  in  Mohr's  burette 
without  undergoing  the  change  peculiar  to  permanganate  :  on  the 
other  hand,  the  end  of  the  reaction  in  the  estimation  of  iron  can 
only  be  known  by  an  external  indicator ;  that  is  to  say,  a  drop  of 
the  mixture  is  brought  in  contact  with  a  drop  of  solution  of  red 
potassic  prussiate  (freshly  prepared)  upon  a  white  slab  or  plate. 
While  the  ferrous  oxide  is  in  tolerable  excess,  a  rich  blue  colour 
occurs  at  the  point  of  contact  between  the  drops ;  but  as  this  excess 
continues  to  lessen  by  the  addition  of  the  bichromate,  the  blue 
becomes  somewhat  turbid,  having  first  a  green,  then  a  grey,  and 
lastly  a  brown  shade.  When  the  greenish-blue  tint  has  all 
disappeared,  the  process  is  finished.  This  series  of  changes  in  the 
colour  admits  of  tolerably  sure  reading  of  the  burette,  after  some 
little  practice  is  obtained. 

The  reaction  between  chromic  acid  and  ferrous  oxide  may  be 
represented  by  the  formula  : 

2Cr03  +  6FeO  =  Cr203  +  3Fe203. 

The  decomposition  takes  place  immediately,  and  at  ordinary 
temperatures,  in  the  presence  of  free  sulphuric  or  hydrochloric  acid. 
Nitric  acid  is  of  course  inadmissible. 

The  reduction  of  ferric  compounds  to  the  ferrous  state  may  be 
accomplished  by  zinc,*  magnesium,  sodic  sulphite,  ammonic 
bisulphite,  or  sulphurous  acid;  or,  instead  of  these,  stannous 
chloride  may  be  used,  which  acts  very  rapidly  as  a  reducing  agent 
upon  ferric  oxide,  the  yellow  colour  of  the  solution  disappearing 
.almost  immediately. 

In  the  analysis  of  iron  ores,  reduction  by  the  latter  is  very 
serviceable ;  the  greatest  care,  however,  is  necessary  that  the 
stannous  chloride  is  not  present  in  excess,  as  this  would  consume 
the  bichromate  solution  equally  with  the  ferrous  oxide,  and  so  lead 
to  false  results. 

The  discharge  of  the  yellow  colour  of  the  iron  solution  may  with 
•care  be  made  a  very  sure  indicator  of  the  exact  point  of  reduction. 
The  concentrated  hydrochloric  solution  of  iron  is  heated  to  gentle 
boiling,  and  the  moderately  dilute  tin  solution  added  with  a  pipette, 
waiting  a  moment  for  each  addition  till  the  last  traces  of  colour 
have  disappeared ;  the  solution  is  then  poured  into  a  beaker,  diluted 

*  When  zinc  is  used,  the  zinc  ferricyanide  somewhat  obsct-.res  the  critical  point  in 
testing  with  the  indicator. 


112  VOLUMETRIC   ANALYSIS.  §    33. 

with  boiled  and  cooled  water,  and  titrated  with  the  bichromate  as 
usual.  An  extra  security  is  obtained  by  adding  a  few  drops  of 
potassic  sulphocyanide  to  the  solution,  the  disappearance  of  the 
blood-red  colour  indicating  that  no  more  ferric  oxide  is  present. 

In  order  to  obviate  the  inaccuracy  which  would  be  produced  by 
an  excess  of  tin  in  the  state  of  protosalt,  Mohr  recommends  that 
chlorine  water  should  be  added  by  drops  to  the  mixture,  until  a 
rod  moistened  with  it  and  brought  in  contact  with  blue  iodide  of 
starch  paper  no  longer  removes  the  colour ;  the  excess  of  stannous 
chloride  is  then  all  converted  into  stannic  chloride,  and  the  titration 
with  bichromate  may  proceed  as  usual. 

It  is  absolutely  necessary  that  the  solution  of  potassic  ferri- 
cyanide  used  as  the  indicator  with  bichromate  should  be  free  from 
ferrocyanide ;  and  as  a  solution  when  exposed  to  air  for  a  short 
time  becomes  in  some  measure  converted  into  the  latter,  it  is 
necessary  to  use  a  freshly  prepared  liquid. 


1.     Preparation  of  the  Decinormal   Solution   of   Bichromate. 
4 -9 13  gin.  per  liter. 

The  reaction  which  takes  place  between  potassic  bichromate  and 
ferrous  oxide  is  as  follows  : — 

6FeO  +  Cr2K207  =  3Fe203  +  Cr203  +  K20 

It  is  therefore  necessary  that  J  eq.  in  grams  should  be  used  for  the 
liter  as  a  normal  solution,  and  -f^  for  the  decinormal ;  and  as  it  is 
preferable  on  many  accounts  to  use  a  dilute  solution,  the  latter  is 
the  more  convenient  for  general  purposes. 

According  to  the  latest  and  most  reliable  researches,  the  equivalent 
number  of  chromium  is  52 '4,  and  consequently  that  of  potassic 
bichromate  is  294*8 ;  if,  therefore,  ^  of  this  latter  number  =  4*9 14 
gm.  be  dissolved  in  a  liter  of  water,  the  decinormal  solution  is 
obtained.  On  the  grain  system,  49*14  grains  to  10,000  grains  of 
water  will  give  the  same  solution.* 

1  c.c.  of  this  solution  is  capable  of  yielding  up  yo-J^Q-  eq.  in 
grams  of  oxygen,  and  is  therefore  equivalent  to  the  yoihnj  e(l'  °^ 
any  substance  which  takes  up  1  equivalent  of  oxygen. 

2.      Solution    of   Stannous    Chloride. 

About  10  gin.  of  pure  tin  in  thin  pieces  are  put  into  a  large 
platinum  capsule,  about  200  c.c.  strong  hydrochloric  acid  poured 
over  it,  and  heated  till  it  is  dissolved ;  or  it  may  be  dissolved  in  a 
porcelain  capsule  or  glass  flask,  adding  pieces  of  platinum  foil 
to  excite  a  galvanic  current.  The  solution  so  obtained  is  diluted  to 

*  Pin-e  bichromate  powdered  and  dried  in  the  air  bath  should  be  used,  and  not  the 
fused  salt. 


§    34  IODOMETRIC    ANALYSES.  113 

al)out  a  liter  with  distilled  water,  and  preserved  in  the  bottle 
(fig.  20)  to  which  the  air  can  only  gain  access  through  a  strongly 
alkaline  solution  of  pyrogallic  acid.  "When  kept  in  this  manner, 
the  strength  will  not  alter  materially  in  a  month.  If  not  so 
preserved,  the  solution  varies  considerably  from  day  to  day,  and 
therefore  should  always  be  titrated  before  use  as  described  in 
§  60.1. 

Examples  of  Iron  Titration :  0'7  gm.  of  pure  and  dry  ammonio-ferrous 
sulphate  =  0'1  gm.  iron,  was  dissolved  in  water,  and  titrated  with  decinormal 
bichromate,  of  which  17*85  c.c.  were  required;  this  multiplied  by  0'0392 
gave  0'699  gm.  instead  of  0'7  gm. 

0'56  gm.  of  iron  wire  required  998  c.c.  =0*5588  gm. ;  as  it  is  impossible 
to  obtain  iron  wire  perfectly  pure,  the  loss  is  undoubtedly  owing  to  the 
impurities. 

If  the  bichromate  solution  should  from  any  accidental  cause  be  found  not 
strictly  of  decinormal  strength,  the  factor  necessary  for  converting  it  must 
be  found  as  previously  described. 

IODINE    AND    SODIC    THIOSTJLPHATE. 

§  34.  THE  principle  of  this  now  beautiful  and  exact  method  of 
analysis  was  first  discovered  by  Dupasquier,  who  used  a  solution 
of  sulphurous  acid  instead  of  sodic  thiosulphate.  Buns  en  im- 
proved his  method  considerably  by  ascertaining  the  sources  of 
failure  to  which  it  was  liable,  which  consisted  in  the  use  of  a  too 
concentrated  solution  of  sulphurous  acid.  The  reaction  between 
iodine  and  very  dilute  sulphurous  acid  may  be  represented  by  the 
formula — 

SO2  + 12  +  2H20  =  2HI  +  H2SO. 

If  the  sulphurous  acid  is  more  concentrated,  i.e.  above  0*04  per 
cent.,  in  a  short  time  the  action  is  reversed,  the  irregularity  of 
decomposition  varying  with  the  quantity  of  water  present,  and  the 
rapidity  with  which  the  iodine  is  added.* 

Sulphurous  acid,  however,  very  rapidly  changes  by  keeping  even 
in  the  most  careful  manner,  and  cannot  therefore  be  used  for  a 
standard  solution.  The  substitution  of  sodic  thiosulphate  is  a  great 
advantage,  inasmuch  as  the  salt  is  easily  obtained  in  a  pure  state, 
and  may  be  directly  weighed  for  the  standard  solution.  The 
reaction  is  as  follows  : — 

2Na2S203  +  21  =  2XaI  +  Xa2S406, 

the  result  being  that  thiosulphuric  acid  takes  oxygen  from  the 
water,  with  the  production  of  tetrathionic  and  hydriodic  acids  in 
combination  with  soda. 

In  order  to  ascertain  the  end  of  the  reaction  in  analysis  by  this 
method  an  indicator  is  necessary,  and  the  most  delicate  and  sensitive 

*  This  irregularity  is  now  obviated  "by  the  method  of  Giles  and  Shearer  (§  72),  in 
which  solutions  of  SQ2  or  sulphites  of  any  strength  may  be  accurately  titrated  with 
iodine,  by  adding  the  latter  to  the  former  in  excess,  and  when  the  reaction  is  complete 
titrating  the  excess  of  iodine  with  thiosiUphate. 

1 


114  VOLUMETRIC   ANALYSIS.  §    34 

for  the  purpose  is  starch,  which  produces  with  the  slightest  trace  of 
free  iodine  in  cold  solution  the  well-known  blue  iodide  of  starch. 
Hydriodic  or  mineral  acids  and  iodides  have  no  influence  upon  the 
colour.  Caustic  alkalies  destroy  it. 

The  principle  of  this  method,  namely,  the  use  of  iodine  as  an 
indirect  oxidizing  body  by  its  action  upon  the  elements  of  water, 
forming  hydriodic  acid  with  the  hydrogen,  and  liberating  the  oxygen 
in  an  active  state,  can  be  applied  to  the  determination  of  a  great 
variety  of  substances  with  extreme  accuracy. 

Bodies  which  take  up  oxygen,  and  decolorize  the  iodine  solution, 
such  as  sulphurous  acid,  sulphites,  sulphuretted  hydrogen,  alkaline 
thiosulphites  and  arsenites,  stannous  chlorides,  etc.,  are  brought 
into  dilute  solution,  starch  added,  and  the  iodine  delivered  in 
with  constant  shaking  or  stirring  until  a  point  occurs  at  which 
a  final  drop  of  iodine  colours  the  whole  blue — a  sign  that  the 
substance  can  take  up  no  more  iodine,  and  that  the  drop  in  excess- 
has  shown  its  characteristic  effect  upon  the  starch. 

Free  chlorine,  or  its  active  compounds,  cannot,  however,  be 
titrated  with  thiosulphate  directly,  owing  to  the  fact  that,  instead  of 
tetrathionic  acid  being  produced  as  with  iodine,  sulphuric  acid  occurs, 
as  may  be  readily  seen  by  testing  with  baric  chloride.  In  such 
cases,  therefore,  the  chlorine  must  be  evolved  from  its  compound 
and  passed  into  an  excess  of  solution  of  pure  potassic  iodide,  where 
it  at  once  liberates  its  equivalent  of  iodine,  which  can  then,  of 
course,  be  estimated  with  thiosulphate. 

All  bodies  which  contain  available  oxygen,  and  which  evolve 
chlorine  when  boiled  with-  strong  hydrochloric  acid,  such  as  the 
chromates,  manganates,  and  all  metallic  peroxides,  can  be  readily 
and  most  accurately  estimated  by  this  method. 

1.      Preparation   of  the   Decinormal   Solution    of  Iodine. 
1  =  126-5  ;  12-65  gin.  per  liter. 

Chemically  pure  iodine  may  be  obtained  by  intimately  mixing  dry 
commercial  iodine  with  about  one-fourth  of  its  weight  of  potassic 
iodide,  and  gently  heating  the  mixture  between  two  large  watch- 
glasses  or  porcelain  capsules ;  the  lower  one  being  placed  upon  a 
heated  iron  plate,  the  iodine  sublimes  in  brilliant  plates,  which  are 
absolutely  pure. 

The  watch-glass  or  capsule  containing  the  iodine  is  placed  under 
the  exsiccator  to  cool,  and  also  to  deprive  it  of  any  traces  of  watery 
vapour;  then  12 -65  gm.  are  accurately  weighed,  and  together  with 
about  18  gm.  of  pure  potassic  iodide  (free  from  iodate)*  dissolved 

*  Morse  and  Burton  (Amer.  CTiem.  Jour.,  1888)  state  that  potassic  iodide  may  be 
completely  freed  from  iodate  by  boiling  a  solution  of  it  with  zinc  amalgam,  prepared 
by  snaking  zinc  dust  in  good  proportion  with  mercury  in  presence  of  tartaric  acid,  and 
washing  with  water.  The  iodate  is  completely  reduced  with  formation  of  zinc  hydroxide. 
The  pure  solution  of  iodide  is  filtered  for  use  through  a  paper  filter  saturated  with  hot 
water. 


§    34  IODOMETEIC    ANALYSES.  115 

in  about  250  c.c.  of  water,  and  diluted  to  exactly  one  liter.  The 
same  solution  may  be  obtained  by  dissolving  126 '5  grains  of  iodine, 
and  180  of  potassic  iodide,  in  10,000  grains  of  water;  in  either 
case  the  solution  is  strictly  decinormal.  The  flask  must  not  be 
heated  in  order  to  promote  solution,  and  care  must  be  taken  that 
iodine  vapours  are  not  lost  in  the  operation. 

The  solution  is  best  preserved  in  stoppered  bottles,  kept  in  the 
dark,  and  which  should  be  completely  filled ;  but  under  any 
circumstances  it  does  not  hold  its  strength  well  for  any  length 
of  time,  and  consequently  should  be  titrated  before  use  in 
analysis. 

Several  substances  have  been  suggested  for  the  verification  of 
iodine  solution,  but  the  preference  should  be  given  to  —^  arsenite 
of  soda,  described  in  §  36.  There  is  no  difficulty  in  procuring 
pure  arsenious  acid,  and  the  alkaline  solution  is  practically  un- 
changeable if  kept  in  well-closed  bottles.  20  c.c.  of  ^  alkaline 
arsenite  should  be  put  into  a  beaker,  diluted,  a  little  solution  of 
ammonic  carbonate  added,  together  with  starch,  and  the  iodine 
added  until  the  blue  colour  is  produced. 

An  alkalimetric  method  is  proposed  by  Kalmann,  in  which  the 
iodine  solution  is  diluted  with  water,  and  H2S  passed  into  the 
liquid  till  colourless;  the  hydriodic  acid  so  produced  is  then 
titrated  with  ~$  alkali  and  methyl  orange. 


2.     Decinormal   Sodic   Thiosulphate. 
Na2S203,5H20  -  248  =  24'8  gm.  per  liter. 

As  it  is  not  difficult  either  to  manufacture  or  procure  pure  sodic 
thiosulphate,  this  quantity,  powdered  and  dried  between  blotting- 
paper,  may  be  weighed  directly,  and  dissolved  in  a  liter  of  distilled 
water,  and  then  titrated  with  the  iodine  solution  and  a  little  starch 
indicator :  or  the  solution  may  be  checked  with  ~  bichromate  as 
recommended  by  Mohr,  by  digesting  a  measured  volume  of 
the  bichromate  with  an  excess  of  potassic  iodide,  and  hydro- 
chloric acid,  in  the  stoppered  flask  (fig.  31)  or  similar  well-closed 
vessel.  When  the  mixture  has  cooled,  the  liberated  iodine  is 
measured  by  the  thiosulphate,  and  its  power  ascertained.  If 
impure  thiosulphate  should  have  been  used,  or  the  sample  was 
not  entirely  free  from  accidental  moisture,  it  will  be  necessary 
to  find  a  factor  by  which  to  reduce  it  to  decinormal  strength, 
as  described  for  previous  solutions ;  or  the  amount  of  impurity 
being  known,  a  fresh  quantity  may  be  prepared  of  proper  strength. 
It  is  advisable  to  preserve  the  solution  in  the  dark.  After  a 
time  all  solutions  of'  thiosulphate  undergo  a  slight  amount  of 
oxidation,  and  sulphur  deposits  upon  the  bottle;  it  is  therefore 
always  better  to  examine  it  previous  to  use.  Mohr  states  that 
the  tendency  to  deposit  sulphur  in  the  solution  may  be  entirely 

i  2 


116  VOLUMETRIC   ANALYSIS.  §    34. 

obviated  by  adding  to  the  —$  solution  sesquicarbonate  of  ammonia, 
in  the  proportion  of  2  grams  to  the  liter.*  Har court  and  Esson 
(Phil.  Trans.  [5]  clvi.  205)  state  that  a  little  caustic  soda  greatly 
increases  the  stability. 

Beside  the  decinormal  iodine  and  thiosulphate,  it  is  convenient 
in  some  cases  to  use  centinormal  solutions,  which  can  readily  be 
prepared  by  diluting  100  c.c.  of  each  decinormal  solution  to 
1  liter. 

In  using  the  iodine  solution  Mohr's  burette  may  be  employed, 
"but  care  must  be  taken  that  the  solution  is  not  left  in  it  for 
any  length  of  time,  as  decomposition  slowly  takes  place,  and  the 
tube  becomes  hard ;  the  tap  burette  is  on  this  account  preferable. 


3.      Starch    Indicator. 

One  part  of  clean  arrowroot,  or  potato  starch,  is  first  mixed 
smoothly  with  cold  water  into  a  thin  paste,  then  gradually  poured 
into  about  150  or  200  times  its  weight  of  boiling  water,  the  boiling 
continued  for  a  minute,  then  allowed  to  stand  and  settle ;  the  clear 
solution  only  is  to  be  used  as  the  indicator,  of  which  a  few  drops 
only  are  necessary,  f  The  solution  may  be  preserved  for  some  time 
by  adding  to  it  about  one  per  cent,  of  salicylic  acid,  or  saturating 
it  with  common  salt;  this,  however,  is  not  so  sensitive  as  the 
freshly  prepared  solution. 

Starch  Paste. — A  very  convenient  form  of  soluble  starch  is  made 
by  mixing  6  gm.  starch  with  100  gm.  pure  glycerine,  heating  for 
an  hour  to  100°  C.,  pouring  into  about  double  its  volume  of  water, 
then  adding  sufficient  strong  alcohol  to  precipitate  the  soluble 
starch,  which  is  filtered  off  and  preserved  in  a  moist  pasty  state. 
When  required,  a  minute  quantity  is  taken  with  a  glass  rod. 

Concentrated  Solution  of  Starch. — This  will  keep  almost  any 
length  of  time.  Made  by  rubbing  about  5  gm.  starch  to  a  smooth 
emulsion,  with  about  50  c.c.  water.  Then  add  25  c.c.  of  50  per 
cent,  solution  of  caustic  potash  and  shake  well,  dilute  with  half  a 
liter  of  water,  boil,  and  allow  to  settle.  This  indicator  answers  very 
well  in  cases  where  the  alkali  is  of  no  consequence,  but  is  not 
available  for  the  delicate  acidimetric  method  by  iodic  acid  unless 
the  alkali  is  exactly  corrected.  It  answers  well,  however,  with  the 
addition  of  2  gm.  of  potassic  iodide  as  a  reagent  for  nitrites,  and 
keeps  perfectly  though  exposed  to  light. 

*  This  has  been  proved  by  my  experiments  not  to  be  correct,  and  Topf  (Z.  a.  C.  xxvi. 
137 — 217)  in  a  long  series  of  experiments  in  iodometry  comes  to  the  same  conclusion. 
Bicarbonate  of  soda  or  potash  have  a  better  effect,  but  even  these  are  open  to  objection. 
It  is  undoubtedly  better  to  make  fresh  solutions  from  pure  thiosulphate  at  intervals  of 
a  month  or  so. 

t  In  iodometric  analyses  it  is  always  advisable  in  titrating  the  free  iodine  with  thio- 
sulphate or  arsenious  solution  to  delay  adding  the  starch  until  the  iodine  colour  is  nearly 
removed :  a  much  more  delicate  ending  may  be  obtained  and  with  very  little  starch. 


§35.  IODOMETPJC    ANALYSES.  117 

ANALYSIS    OF    SUBSTANCES    BY    DISTILLATION    WITH 
HYDROCHLORIC    ACID. 

§  35.     THERE  are  a  great  variety  of  substances  containing  oxygen, 
which  when  boiled  with  hydrochloric  acid  yield  chlorine,  equivalent 


Fig.  29. 

to  the  whole  or  a  part  only  of  the  oxygen  they  contain  according  to 
circumstances.  Upon  this  fact  are  based  the  variety  of  analyses 
which  may  be  accomplished  by  means  of  iodine  and  sodic  thio- 
sulphate,  or  arsenite ;  the  chlorine  so  evolved,  however,  is  not  itself 
estimated,  but  is  conveyed  by  means  of  a  suitable  apparatus  into  a 
solution  of  potassic  iodide,  thereby  liberating  an  equivalent  quantity 
of  iodine.  This  latter  body  is  then  estimated  by  thiosulphate ;  the 
quantity  so  found  is,  therefore,  a  measure  of  the  oxygen  existing  in 
the  original  substance,  and  consequently  a  measure  of  the  substance 
itself.  Analyses  of  this  class  may  be  made  the  most  exact  in  the 
whole  range  of  volumetric  analysis,  far  outstripping  any  process 
by  weight. 

The  apparatus  used  for  distilling  the  substances,  and  conveying 
the  liberated  chlorine  into  the  alkaline  iodide,  may  possess  a  variety 
of  forms,  the  most  serviceable,  however,  being  the  three  kinds 
devised  respectively  by  Bunsen,  Fresenius,  and  Mohr. 

Buns  en's  arrangement  consists  of  an  inverted  retort,  into  the 
neck  of  which  the  tube  from  the  small  distilling  flask  is  passed. 


118 


VOLUMETEIC  ANALYSIS. 


35. 


A  drawing  of  the  entire  apparatus  may  be  seen  in  most  treatises 
on  chemical  analysis. 

Owing  to  the  great  solubility  of  HC1  in  the  form  of  gas,  the 
apparatus  must  be  so  constructed  that  when  all  Cl  is  liberated  and 
HC1  begins  to  distil,  the  liquid  may  not  rush  back  to  the  flask 
owing  to  condensation. 


Pig.  30. 

The  best  preventive  of  this  regurgitation  is,  however,  suggested 
by  Fresenius,  and  applicable  to  each  kind  of  apparatus;  namely, 
the  addition  of  a  few  pieces  of  pure  magnesite.  This  substance 
dissolves  but  slowly  in  the  hydrochloric  acid,  and  so  keeps  up  a 
constant  flow  of  CO2,  the  pressure  of  which  is  sufficient  to  prevent 
the  return  of  the  liquid. 

The  apparatus  contrived  by  Fresenius  is  shown  in  fig.  29,  and 
is  exceedingly  useful  as  an  absorption  apparatus  for  general 
purposes. 

Mohr's  apparatus  is  shown  in  fig.  30  and  is,  on  account  of  its 
simplicity  of  construction,  very  easy  to  use. 

The  distilling  flask  is  of  about  2  oz.  capacity,  and  is  fitted  with  a 


§    35.  IODOMETRIC    ANALYSES.  119 

cork  soaked  to  saturation  in  melted  paraffin ;  through  the  cork  the 
delivery  tube  containing  one  bulb  passes,  and  is  again  passed 
through  a  common,  cork,  fitted  loosely  in  a  stout  tube  about  12  or 
13  inches  long  and  1  inch  wide,  closed  at  one  end  like  a  test  tube. 
This  tube,  containing  the  alkaline  iodide,  is  placed  in  an  hydrometer 
glass,  about  12  inches  high,  and  surrounded  by  cold  water;  the 
delivery  tube  is  drawn  out  to  a  fine  point,  and  reaches  nearly  to 
the  bottom  of  the  condenser.  No  support  or  clamp  is  necessary, 
as  the  hydrometer  glass  keeps  everything  in  position.  The 
substance  to  be  distilled  is  put  into  the  flask  and  covered  with 
strong  hydrochloric  acid,  the  magnesite  added,  the  condenser 
supplied  with  a  sufficient  quantity  of  iodide  solution,  and  the 
apparatus  put  together  tightly.  Either  an  argand  or  common 
spirit  lamp,  or  gas,  may  be  used  for  heating  the  flask,  but  the 
flame  must  be  manageable,  so  that  the  boiling  can  be  regulated  at 
will.  In  the  case  of  the  common  spirit  lamp  it  may  be  held  in  the 
hand,  and  applied  or  withdrawn  according  to  the  necessities  of  the 
case :  the  argand  spirit  or  gas  lamp  can,  of  course,  be  regulated  by 
the  usual  arrangements  for  the  purpose.  If  the  iodine  liberated 
by  the  chlorine  evolved  should  be  more  than  will  remain  in 
solution,  the  cork  of  the  condensing  tube  must  be  lifted,  and  more 
solution  added.  When  the  operation  is  judged  to  be  at  an  end, 
the  apparatus  is  disconnected,  and  the  delivery  tube  washed  out 
into  the  iodide  solution,  which  is  then  emptied  into  a  beaker  or 
flask  and  preserved  for  analysis,  a  little  fresh  iodide  solution  is 
put  into  the  condenser,  the  apparatus  again  put  together,  and  a 
second  distillation  commenced,  and  continued  for  a  minute  or  so, 
to  collect  avery  trace  of  free  chlorine  present.  This  second 
operation  is  only  necessary  as  a  safeguard  in  case  the  first  should 
not  have  been  complete. 

The  solutions  are  then  mixed  together  and  titrated  in  the 
manner  previously  described.  In  all  cases  the  solution  must  be 
cooled  before  adding  the  thiosulphate,  otherwise  sulphuric  acid 
might  be  formed. 

Instead  of  the  large  test  tube,  some  operators  use  a  (J  tube  to 
contain  the  potassic  iodide,  having  a  bulb  in  each  limb,  but  the 
latter  is  not  necessary  if  magnesite  is  used. 

The  solution  of  potassic  iodide  may  conveniently  be  made  of  such 
a  strength  that  -^  eq.  or  33*2  gm.  are  contained  in  the  liter.  1  c.c. 
will  then  be  sufficient  to  absorb  the  quantity  of  free  iodine,  repre- 
senting 1  per  cent,  of  oxygen  in  the  substance  analyzed,  supposing 
it  to  be  weighed  in  the  metric  system.  In  examining  peroxide  of 
manganese,  for  instance,  0'436  gm.  or  4*36  grn.  would  be  used,  and 
supposing  the  percentage  of  peroxide  to  be  about  sixty,  60  c.c.  or 
dm.  of  iodide  solution  would  be  sufficient  to  absorb  the  chlorine 
and  keep  in  solution  the  iodine  liberated  by  the  process ;  it  is 
advisable,  however,  to  have  an  excess  of  iodide,  and,  therefore, 
in.  this  case,  about  70  c.c.  or  dm.  should  be  used.  A  solution  of 


120 


VOLUMETRIC  ANALYSIS. 


indefinite  strength  will  answer  as  well,  so  long  as  enough  is  used  to 
absorb  all  the  iodine.  It  may  sometimes  happen  that  not  enough 
iodide  is  present  to  keep  all  the  liberated  iodine  in  solution,  in 
which  case  it  will  separate  out  in  the  solid  form ;  more  iodide, 
however,  may  be  added  to  dissolve  the  iodine,  and  the  titratioii 
can  then  be  made  as  usual. 

The  process  of  distillation  above  described  may  be  avoided  in 
many  cases.  There  are  a  great  number  of  substances  which,  by 
mere  digestion  with  hydrochloric  acid  and  potassic  iodide  at  an 
elevated  temperature,  undergo  decomposi-  a  ~ 

tion  quite  as  completely  as  by  distillation.   <^J|L  <jL 

For  this  purpose  a  strong   bottle  with  a  C— m „. — — ~  ,, 1 

very  accurately  ground  stopper  is  necessary  ; 
and  as  the  ordinary  stoppered  bottles  of 
commerce  are  not  sufficiently  tight,  it  is 
better  to  re-grind  the  stopper  with  a  little 
very  fine,  emery  and  water.  It  must  then 
be  tested  by  tying  the  stopper  tightly 
down  and  immersing  in  hot  water ;  if  any 
bubbles  of  air  find  their  way  through  the 
stopper  the  bottle  is  useless.  The  capa- 
city may  vary  from  30  to  150  c.c.,  accord- 
ing to  the  necessities  of  the  case. 

The  stopper  may  be  secured  by  fine  copper  binding-wire,  or 
a  kind  of  clamp  contrived  by  Mohr  may  be  used,  as  shown  in 
fig.  31 ;  by  means  of  the  thumb-screws  the  pressure  upon  the 
stopper  may  be  increased  to  almost  any  extent. 

The  substance  to  be  examined,  if  in  powder,  is  put  into  the 
bottle  with  pure  flint  pebbles  or  small  garnets,  so  as  to  divide  it 
better,  and  a  sufficient  quantity  of  saturated  solution  of  potassic 
iodide  and  pure  hydrochloric  acid  added ;  the  stopper  is  then 
inserted,  fastened  down,  and  the  bottle  suspended  in  a  water 
bath,  and  the  water  is  gradually  heated  to  boiling  by  a  gas 
flame  or  hot  plate  as  may  be  most  convenient.  When  the 
decomposition  is  complete  the  bottle  is  removed,  allowed  to  cool 
somewhat,  then  placed  in  cold  water,  and,  after  being  shaken, 
emptied  into  a  beaker,  and  the  liquid  diluted  by  the  washings 
for  titration. 

The  salts  of  chloric,  iodic,  bromic,  and  chromic  acids,  together 
with  many  other  compounds,  may  be  as  effectually  decomposed  by 
digestion  as  by  distillation ;  many  of  them  even  at  ordinary  tem- 
peratures. Recently  precipitated  oxides,  or  the  natural  oxides,, 
when  reduced  to  fine  powder  are  readily  dissolved  and  de- 
composed by  very  weak  acid  in  the  presence  of  potassic  iodide 
(Pickering). 

The  potassic  iodide  used  in  the  various  analyses  must  be  abso- 
lutely free  from  potassic  iodate  and  free  iodine,  or  if  otherwise,  the 
effect  of  the  impurity  must  be  known  by  blank  experiment. 


§    36.  IODOMETRIC    ANALYSES.  121 

ARSENIOTJS    ACID    AND    IODINE. 

§  36.  THE  principle  upon  which  this  method  of  analysis  is 
based  is  the  fact,  that  when  arsenious  acid  is  brought  in  contact 
with  iodine  in  the  presence  of  water  and  free  alkali,  it  is  converted 
into  arsenic  acid,  the  reaction  being — 

As203  +  41  +  2K20  =  As205  +  4KI. 

The  alkali  must  be  in  sufficient  quantity  to  combine  with  the 
hydriodic  acid  set  free,  and  it  is  necessary  that  it  should  exist  in 
the  state  of  bicarbonate,  as  caustic  or  monocarbonated  alkalies 
interfere  with  the  colour  of  the  blue  iodide  of  starch  used  as  indicator. 

If,  therefore,  a  solution  of  arsenious  acid  containing  starch  is 
titrated  with  a  solution  of  iodine  in  the  presence  of  potassic  bicar- 
bonate, the  blue  colour  does  not  occur  until  all  the  arsenious  acid 
is  oxidized  into  arsenic  acid.  In  like  manner,  a  standard  solution 
of  arsenious  acid  may  be  used  for  the  estimation  of  iodine  or  other 
bodies  which  possess  the  power  of  oxidizing  it. 

The  chief  value,  however,  of  this  method  is  found  in  the  estima- 
tion of  free  chlorine  existing  in  the  so-called  chloride  of  lime, 
chlorine  water,  hypochlorites  of  lime,  soda,  etc.,  in  solution; 
generally  included  under  the  term  of  chlorimetry. 

Preparation    of   the    JQ-    Solution    of   Alkaline    Arsenite. 
As203=  198  ;  4-95  gin.  per  liter. 

The  iodine  solution  is  the  same  as  described  in  §  34.1. 

The  corresponding  solution  of  potassic  arsenite  is  prepared  by 
dissolving  4 '95  gm.  of  the  purest  sublimed  arsenious  anhydride  in 
about  250  c.c.  of  distilled  water  in  a  flask,  with  about  20  gm. 
of  pure  potassic  bicarbonate.  It  is  necessary  that  the  acid 
should  be  in  powder,  and  the  mixture  needs  wanning  and  shaking 
for  some  time  in  order  to  complete  the  solution ;  when  this 
is  accomplished  the  mixture  is  diluted  somewhat,  then  made  up  to 
the  liter. 

In  order  to  test  this  solution,  10  c.c.  are  put  into  a  beaker  with 
a  little  starch  indicator,  and  the  iodine  solution  allowed  to  flow  in 
from  a  burette,  graduated  in  -^  c.c.,  until  the  blue  colour  appears. 
If  exactly  10  c.c.  are  required,  the  solution  is  strictly  decinormal ; 
if  otherwise,  the  necessary  factor  must  be  found  for  converting  it 
to  that  strength. 

Starch-paper  Indicator. — Starch  solution  cannot  be  used  for  the 
direct  estimation  of  free  chlorine,  consequently  resort  must  be  had 
to  an  external  indicator ;  and  this  is  very  conveniently  found  in 
starch-iodide  paper,  which  is  best  prepared  by  mixing  a  portion  of 
starch  solution  with  a  few  drops  of  solution  of  potassic  iodide  011 
a  plate,  and  soaking  strips  of  pure  filtering  paper  therein.  The 


122  VOLUMETRIC   ANALYSIS.  §    86. 

paper  so  prepared   is  used  in  the   damp  state,   and  is    far  more 
sensitive  than  when  dried. 

The  Analysis :  In  all  cases  the  chlorine  to  be  estimated  must  exist  in  an 
alkaline  solution.  In  the  case  of  bleaching  powder  this  is  already  accom- 
plished by  the  caustic  lime  which  invariably  exists  in  the  compound. 

The  substance  being  brought  under  the  burette  containing  the  arsenious 
acid  solution,  the  latter  is  suffered  to  flow  until  a  drop  of  the  mixture  taken 
out  with  a  glass  rod  and  brought  in  contact  with  the  prepared  paper,  no 
longer  produces  a  blue  spot.  As  the  colour  becomes  gradually  lighter 
towards  the  end  of  the  process,  it  is  not  difficult  to  hit  the  exact  point ; 
should  it,  howrever,  by  any  accident  be  overstepped,  starch  may  be  added  to 
the  mixture,  and  iodine  solution  added  until  the  blue  colour  is  produced ; 
the  quantity  so  used  is  then  deducted  from  the  total  arsenious  solution. 

Examples :  50  c.c.  of  chlorine  water  were  mixed  with  solution  of  sodic 
carbonate,  and  brought  under  the  arsenic  burette,  and  20  c.c.  of  solution 
added ;  on  touching  the  prepared  paper  with  the  mixture  no  colour  was 
produced,  consequently  the  quantity  used  was  too  great ;  starch  was  therefore 
added,  and  decinormal  iodine,  of  which  3'2  c.c.  were  required  to  produce  the 
blue  colour.  This  gave  16'8  c.c.  of  arsenious  solution,  which  multiplied  by 
0'003537,  gave  0'05942  gin.  of  Cl  in  the  50  c.c.  A  second  operation  with 
the  same  water  required  16'8  c.c.  of  arsenious  solution  direct,  before  the  end  of 
the  reaction  with  iodized  starch-paper  was  reached. 

The  arsenious  solution  is  as  serviceable  as  tliiosulphate  for 
the  general  estimation  of  iodine,  sulphuretted  hydrogen,  chromates, 
etc.,  by  distillation  with  hydrochloric  acid,  and  possesses  the  great 
advantage  of  being  permanent  in  strength  for  almost  any  period 
of  time. 


§    37.  PRECIPITATION    ANALYSES.  123 

PART   IV. 
ANALYSIS   BY   PRECIPITATION. 

§  37.  THE  general  principle  of  this  method  of  determining  the 
quantity  of  any  given  substance  is  alluded  to  in  §  1,  and  in  all 
instances  is  such  that  the  body  to  be  estimated  forms  an  insoluble 
precipitate  with  a  titrated  reagent.  The  end  of  the  reaction  is, 
however,  determined  in  three  ways. 

1.  By  adding  the  reagent  until  no  further  precipitate  occurs, 
as  in  the  determination  of  chlorine  by  silver. 

2.  By  adding  the  reagent  in  the  presence  of  an  indicator  con- 
tained either  in  the  liquid  itself,  or  brought  externally  in  contact 
with  it,  so  that  the  slightest  excess  of  the  reagent  shall  produce  a 
characteristic  reaction  with  the  indicator ;  as  in  the  estimation  of 
silver  with  sodic  chloride  by  the  aid  of  potassic  chromate,  or  with 
thiocyanate  and  ferric  sulphate,  or  that  of  phosphoric  acid  with 
uranium  by  yellow  potassic  prussiate. 

3.  By  adding  the  reagent  to  a  clear  solution,  until  a  precipitate 
occurs,  as  in  the  estimation  of  cyanogen  by  silver. 

The  first  of  these  endings  can  only  be  applied  with  great  accuracy 
to  silver  and  chlorine  estimations.  Very  few  precipitates  have  the 
peculiar  quality  of  chloride  of  silver;  namely,  almost  perfect 
insolubility,  and  the  tendency  to  curdle  closely  by  shaking,  so  as  to 
leave  the  menstruum  clear.  Some  of  the  most  insoluble  precipitates, 
such  as  baric  sulphate  and  calcic  oxalate,  are  unfortunately  excluded 
from  this  class,  because  their  finely  divided  or  powdery  nature 
prevents  their  ready  and  perfect  subsidence. 

In  all  these  cases,  therefore,  it  is  necessary  to  find  an  indicator, 
which  brings  them  into  class  2. 

The  third  class  comprises  only  two  processes ;  viz.,  the  deter- 
mination of  cyanogen  by  silver,  and  that  of  chlorine  by  mercuric 
nitrate. 

Since  the  estimation  of  chlorine  by  precipitation  with  silver,  and 
that  of  silver  by  thiocyanic  acid,  can  be  used  in  many  cases  for 
the  indirect  estimation  of  many  other  substances  with  great  exact- 
ness, the  preparation  of  the  necessary  standard  solutions  will  now 
be  described. 

SILVER    AND    CHLORINE. 

1.      Decinormal    Solution    of    Silver. 

16-966  gm.  AgNO3  per  liter. 

10 '7 6 6  gin.  of  pure  silver  are  dissolved  in  pure  dilute  nitric  acid 
with  gentle  heat  in  a  flask,  into  the  neck  of  which  a  small  funnel 
is  dropped  to  prevent  loss  of  liquid  by  spirting.  When  solution  is 


124  VOLUMETRIC  ANALYSIS.  §    87. 

complete,  the  funnel  must  "be  washed  inside  and  out  with  distilled 
water  into  the  flask,  and  the  liquid  diluted  to  a  liter ;  but  if  it  be 
desired  to  use  potassic  chromate  as  indicator  in  any  analysis,  the 
solution  must  be  neutral ;  in  which  case  the  solution  of  silver  in 
nitric  acid  is  evaporated  to  dryness,  and  the  residue  dissolved  in  a 
liter;  or,  what  is  preferable,  16 '9 6 6  gm.  of  pure  silver  nitrate, 
previously  heated  to  120°  C.  for  10  minutes,  are  dissolved  in  a 
liter  of  distilled  water.  If  the  grain  system  is  used,  107 '66  gm. 
of  silver  or  169*66  grn.  of  nitrate  are  dissolved,  and  the  solution 
diluted  to  10,000  grains. 

2.      Decinormal    Solution    of    Salt. 
5-837  gm.  KaCl  per  liter. 

5 '837  gm.  of  pure  sodic  chloride  are  dissolved  in  distilled  water, 
and  the  solution  made  up  to  a  liter,  or  58 '37  grn.  to  10,000  grains. 
There  are  two  methods  by  which  the  analysis  may  be  ended : 

(a)  By  adding  silver  cautiously,  and  well  shaking  after  each 
addition  till  no  further  precipitate  is  produced.     For  details  see 
§  50. 

(b)  By  using  a  few  drops  of  solution  of  pure  potassic  mono- 
chromate  as  indicator,  as  devised  by  Molir.     If  the  pure  salt  is 
not  at  hand,  some  silver  nitrate  should  be  added  to  the  solution  of 
the  ordinary  salt,  to  remove  chlorine,  and  the  clear  liquid  used. 

The  method  b  is  exceedingly  serviceable,  on  the  score  of  saving 
both  time  and  trouble.  The  solutions  must  be  absolutely  free  from 
acid  or  any  great  excess  of  alkali ;  it  is  best  to  have  them  neutral, 
and  cold.  When,  therefore,  acid  is  present  in  any  solution  to  be 
examined,  it  should  be  neutralized  with  pure  sodic  or  calcic  carbonate 
in  very  slight  excess."55' 

The  Analysis :  To  the  neutral  or  faintly  alkaline  solution,  two  or  three 
drops  of  a  cold  saturated  solution  of  potassic  chromate  are  added,  and  the 
silver  solution  delivered  from  the  burette  until  the  last  drop  or  two  produce 
a  faint  blood-red  tinge,  an  evidence  that  all  the  chlorine  has  combined  with 
the  silver,  and  the  slight  excess  has  formed  a  precipitate  of  silver  chromate ; 
the  reaction  is  very  delicate  and  easily  distinguished.  The  colour  reaction 
is  even  more  easily  seen  by  gas-light  than  by  daylight.  It  may  be  rendered 
more  delicate  by  adopting  the  plan  suggested  by  Dupre  (Analyst,  v.  123). 
A  glass  cell,  about  1  centimeter  in  depth,  is  filled  with  water  tinted  with 
chromate  to  the  same  colour  as  the  solution  to  be  titrated.  The  operation  is 
performed  in  a  white  porcelain  basin.  The  faintest  appearance  of  the  red 
change  is  at  once  detected  on  looking  through  the  coloured  cell.  For  the 
analysis  of  waters  weak  in  chlorine  this  method  is  very  serviceable  (see  §  40). 

Example ;  1  gm.  of  pure  sodic  chloride  was  dissolved  in  100  c.c.  of  water, 
a  few  drops  of  chromate  added,  and  titrated  with  y^  silver,  of  which  17' 1  c.c. 
were  required  to  produce  the  red  colour ;  multiplied  by  the  ^  factor  for  sodic 
chloride  =  0'005837  the  result  was  0'998  gm.  NaCl,  instead  of  1  gm. 

*  Silver  chromate  is  sensibly  soluble  in  the  presence  of  alkaline  or  earthy  nitrates, 
especially  at  a  high  temperature ;  sodic  and  calcic  hydrates  have  the  least  ett'ect ; 
ammonic,  potassic,  and  magnesic  nitrates  the  greatest.  See  also  Carpenter 
(J.  S.  C.  I.  v.  283). 


§    38.  INDIRECT    ESTIMATIONS.  125 

INDIRECT  ESTIMATION  OF  AMMONIA,  SODA,  POTASH, 
LIME,  AND  OTHER  ALKALIES  AND  ALKALINE  EARTHS, 
WITH  THEIR  CARBONATES,  NITRATES,  AND  CHLO- 
RATES, ALSO  NITROGEN,  BY  MEANS  OF  DECINORMAL 
SILVER  SOLUTION,  AND  POTASSIC  CHROMATE,  AS 
INDICATOR. 

1  c.c.  -^j-  silver  solution  =  TTrJ-¥y-  H.  eq.  of  each  substance. 

§  38.  MOHR,  with  his  characteristic  ingenuity,  has  made  use 
of  the  delicate  reaction  between  chlorine  and  silver,  with  potassic 
chromate  as  indicator,  for  the  determination  of  the  bodies  men- 
tioned above.  All  compounds  capable  of  being  converted  into 
neutral  chlorides  by  evaporation  to  dryness  with  hydrochloric  acid 
may  be  determined  with  great  accuracy.  The  chlorine  in  a  com- 
bined state  is,  of  course,  the  only  substance  actually  determined ; 
but  as  the  laws  of  chemical  combination  are  exact  and  well  known, 
the  measure  of  chlorine  is  also  the  measure  of  the  base  with  which 
it  is  combined. 

In  most  cases  it  is  only  necessary  to  slightly  supersaturate  the 
alkali,  or  its  carbonate,  with  pure  hydrochloric  acid  ;  evaporate  on 
the  water  bath  to  dryness,  and  heat  for  a  time  to  120°  C.  in  the  air 
bath,  then  dissolve  to  a  given  measure,  and  take  a  portion  for 
titration. 

Alkalies  and  Alkaline  Earths  with  organic  acids  are  ignited  to 
convert  them  into  carbonates,  then  treated  with  hydrochloric  acid, 
and  evaporated  as  before  described. 

Carbonic  Acid  ill  combination  may  be  determined  by  precipita- 
tion with  baric  chloride,  as  in  §  26.  The  washed  precipitate  is 
dissolved  on  the  filter  with  hydrochloric  acid  (covering  it  with  a 
watch-glass  to  prevent  loss),  and  then  evaporated  to  dryness 
repeatedly  till  all  HC1  is  driven  off.  In  order  to  titrate  with 
accuracy  by  the  help  of  potassic  chromate,  the  baryta  must 
be  precipitated  by  means  of  a  solution  of  pure  sodic  or  potassic 
sulphate,  in  slight  excess;  the  precipitated  baric  sulphate  does 
not  interfere  with  the  delicacy  of  the  reaction.  If  this  precaution 
were  not  taken,  the  yellow  baric  chromate  would  mislead. 

Free  Carbonic  Acid  is  collected  by  means  of  ammonia  and  baric 
chloride  (as  in  §  26),  and  the. estimation  completed  as  in  the  case  of 
combined  CO2. 

Chlorates  are  converted  into  chlorides  by  ignition  before  titration. 

Nitrates  are  evaporated  with  concentrated  hydrochloric  acid,  and 
the  resulting  chlorides  titrated,  as  in  the  previous  case. 


126  VOLUMETRIC  ANALYSIS.  §    38. 

Nitrogen. — The  ammonia  evolved  from  guano,  manures,  oilcakes, 
and  sundry  other  substances,  when  burned  with  soda  lime  in  Will 
and  Varrentrapp's  apparatus,  is  conducted  through  dilute  hydro- 
chloric acid ;  the  liquid  is  carefully  evaporated  to  dryness  before 
titration. 

In  all  cases  the  operator  will,  of  course,  take  care  that  no  chlorine 
from  extraneous  sources  other  than  the  hydrochloric  acid  is  present ; 
or  if  it  exists  in  the  bodies  themselves  as  an  impurity,  its  quantity 
must  be  first  determined. 

Example :  0*25  gm.  pure  sodic  carbonate  was  dissolved  in  water,  and 
hydrochloric  acid  added  till  in  excess ;  it  was  then  dried  on  the  water  bath 
till  no  further  vapours  of  acid  were  evolved ;  the  resulting  white  mass  was 
heated  for  a  few  minutes  to  about  150°  C.,  dissolved  and  made  up  to  300  c.c. 
100  c.c.  required  15*7  c.c.  fV  silver,  this  multiplied  by  3  gave  47'1  c.c.,  which 
multiplied  by  the  YTT  factor  for  sodic  carbonate  =  0'0053,  gave  0'24963  gm. 
instead  of  0'25  gm. 

Indirect  Estimation  of  Potash  and  Soda  existing-  as  Mixed 
Chlorides. — It  is  a  problem  of  frequent  occurrence  to  determine  the 
relative  quantities  of  potash  and  soda  existing  in  mixtures  of  the 
two  alkalies,  such  as  occur,  for  instance,  in  urine,  manures,  soils, 
waters,  etc.  The  actual  separation  of  potash  from  soda  by  means 
of  platinum  is  tedious,  and  not  always  satisfactory. 

The  following  method  of  calculation  is  frequently  convenient, 
since  a  careful  estimation  of  the  chlorine  present  in  the  mixture  is 
the  only  labour  required ;  and  this  can  most  readily  be  accom- 
plished by  ~$  silver  and  chromate,  as  previously  described. 

(1)  The  weight  of  the  mixed  pure  chlorides  is  accurately  found  and  noted. 

(2)  The  chlorides  are  then  dissolved  in  water,  and  very  carefully  titrated 
with  yV  silver  and  chromate  for  the  amount  of  chlorine  present,  which  is- 
also  recorded ;  the  calculation  is  then  as  follows : — 

The  weight  of  chlorine  is  multiplied  by  the  factor  2'103 ;  from  the  product 
so  obtained  is  deducted  the  weight  of  the  mixed  salts  found  in  1.  The  re- 
mainder multiplied  by  3'6288  will  give  the  weight  of  sodic  chloride  present 
in  the  mixture. 

The  weight  of  sodic  chloride  deducted  from  the  total  as  found  in  1  will 
give  the  weight  of  potassic  chloride. 

Sodic  chloride      x   0' 5302  =  Soda  (Na20). 
Potassic  chloride  x   0'6317  =  Potash  (K2O). 

The  principle  of  the  calculation,  which  is  based  on  the  atomic  constitution 
of  the  individual  chlorides,  is  explained  in  most  of  the  standard  works  on 
general  analysis.  Indirect  methods  like  this  can  only  give  useful  result* 
when  the  atomic  weights  of  the  two  substances  differ  considerably,  and  when 
the  proportions  are  approximately  equal. 

Another  method  of  calculation  in  the  case  of  mixed  potassic  and 
sodic  chlorides  is  as  follows  : — 

The  weight  of  the  mixture  is  first  ascertained  and  noted ;  the  chlorine  is 
then  found  by  titration  with  ^  silver,  and  calculated  to  NaCl ;  the  weight 
so  obtained  is  deducted  from  the  original  weight  of  the  mixture,  and  the 
remainder  multiplied  by  2'42857  will  give  the  potassium. 


PRECIPITATION    ANALYSES.  ]  27 


SILVER    AND    THIOCYANTC    ACID. 

§  39.  THIS  process  has  been  devised  by  Volhard  and  is  fully 
described  by  the  author  (JJMffs  Ann.  d.  Cliern.  cxc.  1),  and 
has  been  favourably  noticed  by  Falck  (Z.  a.  C.  xiv.  227), 
Briigelman  (Z.  a.  C.  xvi.  7),  and  Drechsel  (Z.  a.  C.  xvi.  351). 
It  differs  from  Mohr's  chromate  method  in  that  the  silver 
solutions  may  contain  free  nitric  acid. 

This  method  is  based  on  the  fact  that  when  solutions  of  silver 
and  an  alkaline  thiocyanate  are  mixed  in  the  presence  of  a  ferric 
salt,  so  long  as  silver  is  in  excess,  the  thiocyanate  of  that  metal 
is  precipitated,  and  any  brown  ferric  thiocyanate  which  may 
form  is  at  once  decomposed.  "When,  however,  the  thiocyanate  is 
added  in  the  slightest  excess,  brown  ferric  thiocyanate  is  formed, 
and  asserts  its  colour  even  in  the  presence  of  much  free  acid. 
The  method  may  of  course  be  used  for  the  estimation  of  silver, 
and  by  the  residual  process,  for  the  estimation  of  substances  which 
are  completely  precipitated  by  silver. 

It  may  be  used  for  the  estimation  of  silver  in  the  presence  of 
copper  up  to  70  per  cent. ;  also  in  presence  of  antimony,  arsenic, 
iron,  zinc,  manganese,  lead,  cadmium,  bismuth,  and  also  cobalt  and 
nickel,  unless  the  proportion  of  these  latter  metals  is  such  as  to 
interfere  by  intensity  of  colour. 

It  may  further  be  used  for  the  indirect  estimation  of  chlorine, 
bromine,  and  iodine,  in  presence  of  each  other,  existing  either  in 
minerals  or  inorganic  compounds,  and  for  copper  and  zinc ;  these 
will  be  noticed  under  their  respective  heads. 

1.      Decinormal    Ammonic    Thiocyanate. 

This  solution  cannot  be  prepared  by  weighing  the  thiocyanate 
direct,  owing  to  the  deliquescent  nature  of  the  salt ;  but,  supposing 
it  could  be  weighed,  the  quantity  would  be  7 '6  gm.  per  liter; 
therefore  about  8  gm.  of  the  purified  crystals  may  be  dissolved  in 
about  a  liter  of  water  as  a  basis  for  getting  an  exact  solution,  which 
must  be  finally  adjusted  by  a  correct  decinormal  silver  solution. 

The  standard  solution  so  prepared  remains  of  the  same  strength 
for  a  very  long  period  if  preserved  from  evaporation. 

2.      Decinormal    Silver    Solution. 

This  is  the  same  as  described  in  a  preceding  section  (§  37),  and 
may  contain  free  nitric  acid  if  made  direct  from  metallic  silver. 

3.      Ferric    Indicator. 

This  may  consist  simply  of  a  saturated  solution  of  iron  alum ; 
or  may  be  made  by  oxidizing  ferrous  sulphate  with  nitric  acid, 
evaporating  with  excess  of  sulphuric  acid  to  dissipate  nitrous 


128  VOLUMETRIC   ANALYSIS.  §    40. 

fumes,  and  dissolving  the  residue  in  water  so  that  the  strength 
is  about  10  per  cent. 

5  c.c.  of  either  of  these  solutions  are  used  for  each  titration, 
which  must  always  take  place  at  ordinary  temperatures. 

4.      Pure    Nitric    Acid. 

This  must  be  free  from  the  lower  oxides  of  nitrogen,  secured  by 
diluting  the  usual  pure  acid  with  about  a  fourth  part  of  water, 
and  boiling  till  perfectly  colourless.  It  should  then  be  preserved 
in  the  dark. 

The  quantity  of  nitric  acid  used  in  the  titration  may  vary  within 
wide  limits,  and  seems  to  have  no  effect  upon  the  precision  of  the 
method. 

The  Analysis  for  Silver .-  50  c.c.  of  ^  silver  solution  are  placed  into  a 
flask,  diluted  somewhat  with  water,  and  5  c.c.  of  ferric  indicator  added, 
together  with  about  10  c.c.  of  nitric  acid.  If  the  iron  solution  should 
cause  a  yellow  colour,  the  nitric  acid  will  remove  it.  The  thiocyanate 
is  then  delivered  in  from  a  burette ;  at  first  a  white  precipitate  is  produced 
rendering  the  fluid  of  a  milky  appearance,  and  as  each  drop  of  thiocyanate 
falls  in,  it  produces  a  reddish-brown  cloud  which  quickly  disappears  on 
shaking.  As  the  point  of  saturation  approaches,  the  precipitate  becomes 
flocculent  and  settles  easily ;  finally,  a  drop  or  two  of  thiocyanate  produces 
a  faint  brown  colour  which  no  longer  disappears  on  shaking.  If  the 
solutions  are  correctly  balanced,  exactly  50  c.c.  of  thiocyanate  should  be 
required  to  produce  this  effect. 

The  colour  is  best  seen  by  holding  the  flask  so  as  to  catch  the  reflected 
light  of  a  white  wall. 


PRECISION    IN    COLOTJB    REACTIONS. 

§  40.  DUPRE  adopts  the  following  ingenious  method  for  colour 
titrations  (Analyst,  v.  123): — As  is  well  known,  the  change  from 
pale  yellow  to  red,  in  the  titration  of  chlorides  by  means  of  silver 
nitrate  with  neutral  chromate  as  indicator,  is  more  distinctly 
perceived  by  gas-light  than  by  daylight ;  and  in  the  case  of  potable 
waters,  containing  from  one  to  two  grains  of  chlorine  per  gallon,  it 
is  generally  considered  advisable  to  concentrate  by  evaporation 
previous  to  titration,  or  else  to  perform  the  titration  by  gas-light. 
The  adoption  of  the  following  simple  plan  enables  the  operator  to 
perceive  the  change  of  colour  as  sharply,  and  with  as  great  a 
certainty,  by  daylight  as  by  gas-light. 

The  water  is  placed  into  a  white  porcelain  dish  (100  c.c.  are  a 
useful  quantity),  a  moderate  amount  of  neutral  chromate  is  added 
(sufficient  to  impart  a  marked  yellow  colour  to  the  water),  but 
instead  of  looking  at  the  water  directly,  a  flat  glass  cell  containing 
some  of  the  neutral  chromate  solution  is  interposed  between  the 
eye  and  the  dish.  The  effect  of  this  is  to  neutralize  the  yellow 
tint  of  the  water ;  or,  in  other  words,  if  the  concentration  of  the 
solution  in  the  cell  is  even  moderately  fairly  adjusted  to  the  depth 


§    41.  THE    COLORIMETER.  129 

of  tint  imparted  to  the  water,  the  appearance  of  the  latter,  looked 
at  through  the  cell,  is  the  same  as  if  the  dish  were  filled  with  pure 
water.  If  now  the  standard  silver  solution  is  run  in,  still  looking 
through  the  cell,  the  first  faint  appearance  of  a  red  coloration 
becomes  strikingly  manifest;  and  what  is  more,  when  once  the 
correct  point  has  been  reached  the  eye  is  never  left  in  doubt,  how- 
ever long  we  may  be  looking  at  the  water.  A  check  experiment 
in  which  the  water,  with  just  a  slight  deficiency  of  silver,  or  excess 
of  chloride,  is  used  for  comparison  is  therefore  unnecessary. 

A  similar  plan  will  be  found  useful  in  other  titrations.  Thus, 
in  the  case  of  turmeric,  the  change  from  yellow  to  brown  is  per- 
ceived more  sharply  and  with  greater  certainty  when  looking 
through  a  flat  cell  containing  tincture  of  turmeric  of  suitable 
concentration  than  with  the  naked  eye.  The  liquid  to  be  titrated 
should,  as  in  the  former  case,  be  placed  into  a  white  porcelain  dish. 
Again,  in  estimating  the  amount  of  carbonate  of  lime  in  a 
water  by  means  of  decinormal  acid  and  cochineal,  the  exact 
point  of  neutrality  can  be  more  sharply  fixed  by  looking  through 
the  cell  filled  with  a  cochineal  solution.  In  this  case  the  following 
plan  is  found  to  answer  best.  The  water  to  be  tested — about 
250  c.c. — is  placed  into  a  flat  porcelain  evaporating  dish,  part  of 
which  is  covered  over  with  a  white  porcelain  plate.  The  water  is 
now  tinted  with  cochineal  as  usual,  and  the  sulphuric  acid  run  in, 
the  operator  looking  at  the  dish  through  the  cell  containing  the 
neutral  cochineal  solution.  At  first  the  tint  of  the  water  and  the 
tint  in  which  the  porcelain  plate  is  seen  are  widely  different ;  as 
however,  the  carbonate  becomes  gradually  neutralized,  the  two 
tints  approach  each  other  more  and  more,  and  when  neutrality  is 
reached  they  appear  identical ;  assuming  that  the  strength  of  the 
cochineal  solution  in  the  cell,  and  the  amount  of  this  solution 
added  to  the  water,  have  been  fairly  well  matched.  Working  in 
this  manner  it  is  not  difficult  (taking  ^  liter  of  water)  to  come 
within  O'l  c.c.  of  decinormal  acid  in  two  successive  experiments, 
and  the  difference  need  never  exceed  0*2  c.c.  In  the  cell  employed 
the  two  glass  plates  are  a  little  less  than  half  an  inch  apart. 

A  somewhat  similar  plan  may  be  found  useful  in  other  titrations, 
or,  in  fact,  in  many  operations  depending  on  the  perceptions  of 
colour  change. 


THE    COLORIMETER. 

§  41.  SEVERAL  methods  of  analysis  by  colour  titration  are 
given  in  the  following  pages,  and  therefore  it  is  only  appropriate 
that  any  convenient  instrument  which  may  facilitate  these  methods 
should  be  described. 

Several  varieties  of  form  have  been  devised  by  operators,  but 
the  principle  is  the  same ;  and  as  Dr.  Mills  has  given  some  con- 
siderable attention  to  the  subject,  and  his  instrument  has  found 

K 


130 


VOLUMETRIC  ANALYSIS. 


§    41. 


acceptance   with    chemists    generally,    the    following    details    are 
given. 

Mills 's  detached  colorimeter  is  made  in  two  pieces,  alike  in 
every  respect ;  one  of  these  is  represented  in  the  subjoined  figure. 
It  consists  of  a  stout  glass  tube  having  a  broad  flat  foot,  and 
graduated  into  100  equal  parts;  its  capacity  is  about  120  c.c. 
On  the  top  of  this  is  a  loosely  fitting  brass  cap, 
prolonged  downwards  so  as  to  cover  and  shade 
the  surface  of  the  liquid,  thereby  preventing 
the  appearance  of  a  dark  meniscus.  The  surface 
of  the  liquid  is  only  visible  sideways  through 
the  little  aperture  cut  out  for  that  purpose. 
The  cap  is  perforated  centrally :  and  a  short 
tube  rises  from  the  perforation.  This  tube  is 
soldered  laterally  to  a  narrower  one,  and  this 
again  to  a  small  block,  from  which  rises  a  spring 
carrying  another  small  block.  The  narrower 
tube  has,  cemented  into  it,  a  glass  tube, 
which  passes  straight  downwards,  and  reappears 
below  the  flat  surface  of  the  cap,  its  end  amply 
clearing  that  surface.  This  tube  is  coned  out- 
wards at  its  upper  extremity,  but  is  left  plain 
below.  Through  it  there  passes,  with  just 
sufficient  room  to  move,  a  rod,  bent  below 
twice  at  right  angles,  so  as  to  carry  a  flat  circular 
opal  glass  disk,  to  which  it  is  attached  by 
fusion.  These  disks  are  turned  in  the  lathe  : 
their  surfaces  should  be  polished  free  from 
scratches,  and  their  edges  show  no  bevel.  The 
rod  is  prevented  from  falling  by  the  easy 
pressure  of  a  little  half -tube,  carried  by  the  small 
block.  When  the  thumb  and  forefinger  are 
lightly  pressed  on  each  side  of  the  cap,  the  rod 
can  be  readily  moved  up  and  down,  and  will 
then  stay  in  any  position  in  which  it  may  have 
been  left.  It  is  convenient  to  cone  outwards  the  half-tube  at  both 
its  ends ;  but  only  traces  of  liquid  ever  reach  this  spot. 

The  instrument  has  two  accessories  which  are  of  considerable 
service.  These  consist  (1)  of  a  pair  of  glass  disks,  lying  at  the 
bottom  of  the  tube,  one  having  a  suitable  red,  the  other  a  green 
colour ;  there  is  thus  obtained  a  black  ground,  on  which  the  opal 
disk  is  always  seen  through  the  upper  opening.  An  annulus  of 
deeper  tint  than  a  given  observed  colour  would  otherwise  surround 
the  opal  disk,  and  tend  to  confuse  the  determination.  It  is  an 
advantage  at  times  to  use  other  colours,  and  even  to  cover  the 
opal  disk  with  a  plate  of  coloured  glass.  The  other  accessory 
is  (2)  a  black  hemispherical  button.  This  lies  loosely  on  the 
opal  disk,  as  shown  in  the  figure.  It  is  used  in  the  estimation 


Fig.  30. 


§    41.  THE    COLORIMETEK.  131 

of  turbidities  (i.e.  precipitates)  by  lowering  it  until  its  point  just 
disappears. 

In  taking  readings,  the  position  of  the  flat  surface  with  regard 
to  the  scale  is  always  the  object  to  be  ascertained ;  and  this  can  be 
done,  as  is  the  case  with  Erdmann's  float,  so  as  entirely  to  avoid 
parallax.  The  level  of  the  liquid's  surface  is  afterwards  taken; 
and  the  difference  between  the  two  readings  is  the  depth  required ; 
but  if  the  button  be  used,  the  height  of  the  button  must  be 
subtracted  from  that  difference. 

It  is,  of  course,  obvious  that  any  upward  or  downward  movement 
of  the  rod  must  alter  somewhat  the  level  of  the  surface  of  the 
liquid.  For  small  variations  thus  produced  (as,  for  example,  by 
a  depression  of  two  or  three  divisions)  no  correction  need  be  made. 
For  larger  variations  a  factor  is  easily  found  by  experiment ;  it  is 
probably  the  same  in  every  specimen  of  the  instrument,  viz.,  nearly 
O015  division  for  every  division  the  rod  is  moved.  This  correction 
is  perhaps  rather  better  than  direct  reading. 

The  colorimeter  has  been  of  late  years  more  extensively  used 
than  formerly ;  but  it  would  probably  be  much  more  widely 
employed  if  its  service  were  better  understood.  Thus,  for  example, 
a  red  liquid  like  a  solution  of  magenta  is  admirably  suited  for 
colorimetric  measurement,  it  having  a  tint  to  which  the  eye  readily 
adapts  itself.  On  the  other  hand,  it  is  rare  to  find  any  one  who 
can  accurately  estimate  yellow.  Something  thus  depends  on  the 
eye,  and  on  the  employment  of  the  same  eye.  It  must  also  be 
borne  in  mind  that  very  few  liquids  will  stand  a  dilution  of  over 
20  per  cent,  without  undergoing  chemical  change.  Thus,  a  very 
Aveak  solution  of  magenta  differs  in  actual  colour  from  a  strong  one. 
Hence  it  is  obviously  necessary  to  use  the  first  determination  as  a 
mere  approximation  ;  and,  on  that  as  a  basis,  to  alter  the  strengths 
of  the  standard  and  trial  liquid  to  equality.  A  second  determina- 
tion is  now  made,  and  a  still  closer  approximation  obtained  by  its 
means.  This  process  being  repeated  until  there  is  only  a  difference 
of  a  division  or  two  between  the  two  liquids. 

The  second  approximation  will  in  general  be  found  sufficiently 
exact.  All  dilutions  should,  as  far  as  possible,  have  the  same  age. 
With  regard  to  the  standard  tint  selected,  the  operator  has  in  this 
colorimeter  the  means  of  varying  his  standard  to  any  extent  by 
shifting  one  opal  disk ;  he  can  thus  work  at  the  particular  depth  of 
tint  which  he  finds  most  suitable  to  his  own  eye.  Steady  accuracy 
in  any  particular  measurement  can  generally  be  obtained  by  at 
most  a  few  days'  practice. 

Turbidities. — A  black  or  coloured  disk,  lowered  through  a  turbid 
liquid,  eventually  vanishes,  and  the  depth  at  which  disappearance 
takes  place  is  a  measure  of  the  amount  of  turbidity  present. 
In  this  way,  for  example,  it  is  easy  to  estimate  the  amount  of  water 
added  to  milk.  It  is  obvious,  however,  that  this  method  admits  of 

K  2 


132  VOLUMETKIC  ANALYSIS.  §    41. 

quantitative  extension  to  all  sorts  of  precipitates,  provided  we  can 
find  a  suitable  medium  to  ensure  their  suspension  as  a  turbidity, 
and  not  in  the  aggregated  state,  during  a  suitable  time. 

The  suspensory  liquid  consists  of  100  gm.  of  gelatine,  100  gin. 
at  most  of  glacial  acetic  acid,  and  1  gm.  of  salicylic  acid,  dissolved 
in  a  liter  of  distilled  water ;  this  is  clarified  with  a  little  white  of 
egg,  and  filtered  hot.  It  remains  permanently  liquid  in  the  cold, 
and  does  not  putrefy.  It  may,  if  desired,  be  charged  with  any 
special  reagent  (baric  chloride  for  instance) ;  a  volume  of  the 
mixture  can  then  be  added  to  a  volume  of  a  very  weak  standard 
sulphate,  and  also  to  a  volume  of  sulphate  of  unknown  strength  ; 
by  depressing  the  black  buttons,  the  colorimeters  determine  the 
relation  between  the  two.  The  reacting  bodies  should  in  such 
cases  be  the  same ;  thus,  hydric  sulphate  should  not  be  compared 
against  potassic  sulphate.  The  key  to  success  in  colorimetry  is,  in 
fact,  equality  of  condition. 

If  the  precipitant  should  be  alkaline,  or  an  alkaline  carbonate, 
the  gelatine  solution  should  first  be  neutralized,  and  then  mixed 
with  more  alkali  or  carbonate.  Such  solutions  as  aqueous  magnesic 
chloride  and  zinc  sulphate  can  then  be  added,  the  whole  instantly 
well  shaken,  and  the  result  compared  with  a  standard  effect  in  the 
other  tube. 

Lime  can  be  determined  by  adding  ammonia  and  ammonic  oxalate 
to  the  suspensory  liquid,  and  then  a  weak  solution  of  calcic  salt. 

There  is  probably  no  substance  incapable  of  suspension  for  more 
than  half  an  hour — a  period  sufficient  for  thirty  comparisons ;  and 
most  precipitates  will  refuse  to  fall  for  hours,  sometimes  for  days, 
together.  Traces  of  argentic  chloride  will  remain  unprecipitated  in 
this  liquid  for  months.  The  operator  has  therefore  only  to  select 
such  a  strength  of  standard  precipitate  as  shall  give  him  not  too 
great  an  amount  to  suspend,  and  an  opacity  equal  to  about  fifty 
scale-divisions.  If  the  substance  precipitated  should  be  soluble  in 
the  solution  of  gelatine,  that  solution  should  be  saturated,  before 
use,  with  the  precipitate  in  question. 

The  colorimeter  is  an  instrument  admirably  adapted  for  use  in 
comparatively  unskilled  hands,  and  especially  in  those  industrial 
analyses  where  one  class  of  product  is  constantly  tested  by  a  single- 
person. 

Directions    for    Use. 

1.  Clear  Liquids. — The  two  coloured  disks  are  put  in  first.  The  cap  is 
then  placed  on  one  of  the  tubes,  and  the  piston  pushed  down  as  far  as  it  will 
go,  the  little  window  being  over  the  scale.  A  clear  coloured  solution  of 
known  strength  is  poured  in  through  the  brass  tube  at  the  top,  until  the 
mark  100  is  exactly  reached.  The  tube  is  then  placed  on  a  table,  preferably 
behind  a  ground-glass  window,  and  the  piston  moved  to  a  position  such  that, 
on  looking  down  at  it  with  one  eye,  the  visible  depth  of  tint  is  easy  to 
remember.  The  other  tube  is  similarly  filled  with  the  solution  of  unknown 
strength,  and  placed  beside  the  first ;  its  piston  is  raised  until,  when  observed 


§   41.  THE    COLORIMETEK.  133 

with  the  same  eye,  the  depth  of  tint  in  both  tubes  appears  to  be  the  same. 
This  depth  is  taken  by  subtracting  the  scale-reading  opposite  the  piston's 
top  from  the  reading  at  the  level  of  the  surface  of  the  liquid.  The  relative 
strengths  of  the  liquids  are  inversely  as  the  depths.  Thus  the  standard 
being  50,  and  containing  2  per  cent.,  the  other  solution  reads  75;  its  strength 
was  therefore  75  :  50  :  :  2%  :  1'33°/0.  It  is  well  to  work  with  different 
depths  of  the  standard  tint,  and  take  the  mean  of  the  results.  If  the 
strengths  differ  by  more  than  10  per  cent.,  they  should  be  adjusted  by 
dilution  to  less,  and  re-determined. 

2.  Turbid  Liquids. — Milks  are  examined  by  diluting  them  100  times, 
and  comparing  them  with  a  milk  of  known  strength,  equally  diluted.  The 
comparison  is  made  by  lowering  a  black  button  through  the  liquid,  until  its 
rounded  top  just  disappears.  The  calculation  is  made  as  above.  Colourless 
metallic  solutions  are  examined  by  precipitating  them  with  some  suitable 
reagent,  and  shaking  with  an  equal  volume  of  a  10-per-cent.  acetic  solution 
of  gelatine ;  the  turbid  liquid  thus  made  is  compared  with  a  similar  prepara- 
tion of  known  strength,  by  lowering  the  black  buttons. 


134  VOLUMETRIC  ANALYSIS.  8   42. 


PART    V. 

APPLICATION   OF   THE   FOREGOING   PRINCIPLES   OF 
ANALYSIS    TO    SPECIAL   SUBSTANCES. 

ANTIMONY. 


1.      Conversion    of    Antimonious    Acid    in    Alkaline    Solution    into 
Antimonic    Acid    by    Iodine    (Mohr). 

§  42.  ANTIMONIOUS  oxide,  or  any  of  its  compounds,  is  brought 
into  solution  as  tartrate  by  tartaric  acid  and  water  ;  the  excess  of 
acid  neutralized  by  sodic  carbonate  ;  then  a  cold  saturated  solution 
of  sodic  bicarbonate  added,  in  the  proportion  of  10  c.c.  to  about 
O'l  gm.  Sb203;  to  the  clear  solution  -~$  iodine  and  starch  are 
added  until  the  blue  colour  occurs.  No  delay  must  occur  in  the 
titration  when  the  bicarbonate  is  added,  otherwise  a  portion  of  the 
metal  is  precipitated  as  antimonious  hydrate,  upon  which  the  iodine 
has  little  effect.* 

For  the  estimation  of  antimonic  acid  and  its  salts,  G.  von  Knorre 
(Zeit,  Angeiv.  CJiem.,  1888,  155)  gives  the  following  method  as 
accurate  :  — 

The  solution  of  the  salt,  strongly  acidified  with  hydrochloric  acid,  is  treated 
in  a  roomy  flask  with  strong  solution  of  sodic  sulphite,  added  gradually  in 
small  portions.  It  is  then  vigorously  boiled  until  all  SO2  is  expelled,  a  drop 
of  phenolphthalein  is  added,  then  caustic  potash  until  red  ;  this  is  in  turn 
removed  by  a  small  excess  of  tartaric  acid.  Sodic  bicarbonate  is  then  added, 
and  the  titration  with  iodine  carried  out  in  the  usual  way. 

The  colour  disappears  after  a  little  time,  therefore  the  first 
appearance  of  a  permanent  blue  is  accepted  as  the  true  measure 
of  iodine  required. 

1  c.c.  /o-  iodine  =  0-0060  gm.  Sb. 

Estimation   of   Antimony  in   presence   of   Tin    (Type   and 
Britannia  metal,    etc.). 

The  finely  divided  alloy  is  dissolved  in  strong  hydrochloric  acid 
by  heat,  adding  frequently  small  quantities  of  potassic  chlorate. 
The  liquid  is  boiled  to  remove  free  chlorine,  cooled,  a  slight  excess 

*  Dunstan  and  Boole  (Pharm.  Jour.,  Nov.  1888)  have  proved  that  the  accurate 
estimation  of  the  antimony  in  tartar  emetic  may  be  secured  by  this  method,  using  the 
precautions  above  mentioned. 


§    42.  ANTIMONY.  135 

of  strong  solution  of  potassic  iodide  added,  and  the  liberated  iodine 
estimated  by  standard  thiosulphate.  Some  operators  prefer  to 
collect  the  liberated  iodine  in  carbon  bisulphide  previous  to 
titration. 

120  Sb  liberate  253  I,  and  the  weight  of  I  found  multiplied 
by  0-475  =  Sb. 

If  iron  or  other  metal  capable  of  liberating  iodine  be  present, 
treat  the  alloy  with  nitric  acid,  and  evaporate  to  obtain  the  oxides 
of  antimony  and  tin — wash,  boil  in  hydrochloric  acid,  and  proceed 
as  before  described.  The  rationale  is,  that  antimonic  chloride  is 
reduced  to  antimonious  chloride,  while  stannic  chloride  is  not 
affected. 


2.    Oxidation  by  Potassic  Bichromate  or  Permanganate  (Kessler). 

Bichromate  or  permanganate  added  to  a  solution  of  antimonious 
chloride,  containing  not  less  than  j-  of  its  volume  of  hydrochloric 
acid  (sp.  gr.  1*12),  converts  it  into  antimonic  chloride. 

The  reaction  is  uniform  only  when  the  minimum  quantity  of  acid 
indicated  above  is  present,  but  it  ought  not  to  exceed  |-  the  volume, 
and  the  precautions  before  given  as  to  the  action  of  hydrochloric 
acid  on  permanganate  must  be  taken  into  account,  hence  it  is 
preferable  to  use  bichromate. 

Kessler  (Poggend.  Annal.  cxviii.  17)  has  carefully  experimented 
upon  this  method  and  adopts  the  following  processes. 

A  standard  solution  of  arsenious  acid  is  prepared  containing  5  gm. 
of  the  pure  acid,  dissolved  by  the  aid  of  sodic  hydrate,  neutralized 
with  hydrochloric  acid,  100  c.c.  concentrated  hydrochloric  acid 
added,  then  diluted  with  water  to  1  liter ;  each  c.c.  of  this  solution 
contains  O'OOS  gm.  As203,  and  represents  exactly  0*007253  gm. 
Sb203. 

Solutions  of  potassic  bichromate  and  ferrous  sulphate  of  known 
strength  in  relation  to  each  other,  are  prepared  in  the  usual  way ; 
and  a  freshly  prepared  solution  of  potassic  ferricyanide  used  as 
indicator. 

The  relation  between  the  bichromate  and  arsenious  solution  is 
found  by  measuring  10  c.c.  of  the  latter  into  a  beaker,  20  c.c. 
hydrochloric  acid  of  sp.  gr.  1*12,  and  from  80  to  100  c.c.  of  water 
(to  insure  uniformity  of  action  the  volume  of  HC1  must  never  be 
less  than  J  or  more  than  i) ;  the  bichromate  solution  is  then  added 
in  excess,  the  mixture  allowed  to  react  for  a  few  minutes,  and  the 
ferrous  solution  added  until  the  indicator  shows  the  blue  colour. 
To  find  the  exact  point  more  closely,  -|  or  1  c.c.  bichromate  solution 
may  be  added,  and  again  iron,  until  the  precise  ending  is  obtained. 

The  Analysis :  The  material,  free  from  organic  matter,  organic  acids,  or 
heavy  metals,  is  dissolved  in  the  proper  proportion  of  HC1,  and  titrated 
precisely  as  just  described  for  the  arsenious  solution;  the  strength  of  the 


136  VOLUMETRIC   ANALYSIS.  §    43. 

bichromate  solution  having  been  found  in  relation  to  AscO3  the  calculation 
as  respects  Sb-O3  presents  no  difficulty.  Where  direct  titration  is  not 
possible  the  same  course  may  be  adopted  as  with  arsenic  (§  43.2)  ;  namely, 
precipitation  with  H2S  and  digestion  with  mercuric  chloride. 

In  the  case  of  using  permanganate  it  is  equally  necessary  to  have 
the  same  proportion  of  HC1  present  in  the  mixture,  and  the 
standard  solution  must  be  added  till  the  rose  colour  is  permanent. 
The  permanganate  may  be  safely  used  with  J  the  volume  of  HC1, 
with  the  addition  of  some  inagnesic  sulphate,  and  as  the  double 
tartrate  of  antimony  and  potassium  can  readily  be  obtained  pure, 
and  the  organic  acid  exercises  no  disturbing  effect  in  the  titration, 
it  is  a  convenient  material  upon  which  to  standardize  the  solution. 


3.  Distillation  of  Antimonious  or  Antimonic  Sulphide  -with. 
Hydrochloric  Acid,  and  Titration  of  the  evolved  Sulphuretted 
Hydrogren  (Schneider). 

When  either  of  the  sulphides  of  antimony  is  heated  with 
hydrochloric  acid  in  Bunsen's,  Fresenius',  or  Mohr's  distilling 
apparatus  (§  35),  for  every  1  eq.  of  antimony  present  as  sulphide, 
3  eq.  of  H2S  are  liberated.  If,  therefore,  the  latter  be  estimated, 
the  quantity  of  antimony  is  ascertained.  The  process  is  best  con- 
ducted as  follows : — 

The  antimony  to  be  determined  is  brought  into  the  form  of  ter-  or  penta- 
sulphide  (if  precipitated  from  a  hydrochloric  solution,  tartaric  acid  must  be 
previously  added  to  prevent  the  precipitate  being  contaminated  with  chloride), 
which,  together  with  the  filter  containing  it,  is  put  into  the  distilling  flask 
with  a  tolerable  quantity  of  hydrochloric  acid  not  too  concentrated.  The 
absorption  tube  contains  a  mixture  of  caustic  soda  or  potash,  with  a  definite 
quantity  of  ^  arsenious  acid  solution  (§  36)  in  sufficient  excess  to  retain  all 
the  sulphuretted  hydrogen  evolved.  The  flask  is  then  heated  to  boiling,  and 
the  operation  continued  till  all  evolution  of  sulphuretted  hydrogen  has  ceased ; 
the  mixture  is  then  poured  into  a  beaker,  and  acidified  with  hydrochloric 
acid,  to  precipitate  all  the  arsenious  sulphide.  The  whole  is  then  diluted  to, 
say  300  c.c  ,  and  103  c.c.  taken  with  a  pipette,  neutralized  with  sodic  carbonate, 
some  bicarbonate  added,  and  the  titration  for  excess  of  arsenious  acid 
performed  with  ^r  iodine  and  starch,  as  directed  in  §  36.  The  separation  of 
antimony  may  generally  be  insured  by  precipitation  as  sulphide.  If  arsenic 
is  precipitated  at  the  same  time,  it  may  be  removed  by  treatment  with 
ammonic  carbonate. 

ARSENIC. 

As  =  75.     As203  =  198.     As205  =  230. 
1.      Oxidation    by    Iodine    (Mohr). 

§  43.  THE  principle  upon  which  the  determination  of  arsenious 
acid  by  iodine  is  based  is  explained  in  §  36. 

Experience  has  shown,  that  in  the  estimation  of  arsenious 
compounds  by  the  method  there  described,  it  is  necessary  to  use 


§    43.  ARSENIC.  137 

sodic  bicarbonate  for  rendering  the  solution  alkaline  as  in  the  case 
of  antimony. 

The  Analysis  :  To  a  neutral  aqueous  solution,  add  about  20  c.c.  of  saturated 
solution  of  pure  bicarbonate  to  every  O'l  gin.  or  so  of  As"2O3,  and  then  titrate 
with  y^  iodine  and  starch.  AVhen  the  solution  is  acid,  the  excess  may  be 
removed  by  neutral  sodic  carbonate,  then  the  necessary  quantity  of  bicar- 
bonate added,  and  the  titration  completed  as  before. 

The  titration  of  arsenic  acid  is  best  done  by  dissolving  the  acid  in  water, 
and  boiling  with  potassic  iodide  in  the  presence  of  hydrochloric  acid  in  large 
excess  until  all  iodine  vapours  are  dissipated.  The  AsHO4  is  completely 
reduced  to  AsHO3.  The  liquid  is  then  cooled,  sodic  carbonate  added  to 
neutrality,  then  some  bicarbonate,  and  the  arsenious  acid  titrated  with 
iodine  in  the  usual  way.  Younger  (J.  S.  C.  I.  ix.  158)  has  verified  this 
method  and  proved  that  the  reduction  is  complete  :  he  also  states  that  when 
the  boiled  solution  cools,  the  liberation  of  a  slight  amount  of  iodine  occurs, 
which  may  be  prevented  by  using  a  few  c.c.  of  glycerine.  Of  course  the 
arsenic  acid  must  contain  no  nitric  acid,  nitrates,  or  similar  interfering  bodies. 

1  c.c.  ^  iodine  =  0-00495  gin.  As203,  or  0*00575  gm.  As205. 

Titration  of  Alkaline  Arseniates. — 111  the  fourth  edition  of  this 
book  it  was  recommended,  on  the  authority  of  Barnes,  to  estimate 
the  arsenic  acid  in  commercial  arseiiiates  of  soda,  etc.,  oy  reduction 
with  sulphurous  acid  (passing  the  gas  through  the  liquid),  boiling 
off  the  excess  of  SO2,  neutralizing  with  sodic  bicarbonate,  and 
titrating  with  iodine  as  described  above.  This  method  has  not 
given  me  satisfactory  results.  The  mere  passing  the  gaseous  SO2 
through  the  liquid  does  not,  in  all  cases,  insure  the  complete 
reduction  to  arsenious  acid. 

Holthof  (Z.  a.  C.  xxii.  378)  and  McKay  (C.  N.  liii.  221—243) 
have  experimented  largely  on  this  method  of  estimating  arsenic, 
which  was  really  originally  suggested  by  Mohr,  but  never  widely 
adopted,  owing  to  the  defect  already  mentioned.  Holthof  proved 
that  various  forms  of  arsenic,  on  being  converted  into  arsenic  acid, 
would  bear  evaporation  to  dryness  with  HC1  without  loss,  and  that 
arsenic  sulphide  coidd  be  oxidized  by  strong  nitric  acid,  or  Avith 
HC1  and  KC103  to  arsenic  acid,  and  reduced  to  the  lower  state  of 
oxidation  by  copious  treatment  with  SO2,  the  method  being  to  add 
300  or  400  c.c.  of  strong  solution  of  SO2,  digest  on  the  water  bath 
for  two  hours,  then  boil  down  to  one-half,  and  when  cool  add 
sodic  bicarbonate,  and  titrate  with  iodine  and  starch. 

McKay  shortens  the  method  considerably  by  placing  the  mixture 
in  a  wTell-stoppered  bottle,  tying  down  the  stopper,  and  digesting  in 
boiling  water  for  one  hour.  At  the  end  of  that  time  the  bottle  is 
removed  and  allowed  to  cool  somewhat,  then  emptied  into  a  boiling 
flask,  diluted  with  about  double  its  volume  of  water,  and  boiled 
down  by  help  of  a  platinum  spiral  to  one-half.  The  liquid  is 
cooled,  diluted,  and  either  the  whole  or  an  aliquot  portion  titrated 
in  the  usual  way. 

For  quantities  of  material  representing  about  0*1  gm.  As,  30  c.c. 


138  VOLUMETRIC  ANALYSIS.  §    43. 

of  saturated  solution  of  SO2  will  suffice,  and  the  reduction  may 
therefore  be  made  in  a  bottle  holding  50  or  60  c.c.  (§  35).  The 
results  are  very  satisfactory.  In  the  case  of  titrating  commercial 
alkaline  arseniates,  which  often  contain  small  quantities  of 
arsenious  acid,  this  must  be  estimated  first,  and  the  amount 
deducted  from  the  total  obtained  after  reduction. 

2.      Oxidation    by    Potassic    Bichromate    (K  easier). 

This  method  is  exactly  the  same  as  is  fully  described  in  §  42  for  antimony. 

The  arsenious  compound  is  mixed  with  ^  bichromate  in  excess  in  presence 
of  hydrochloric  aci  and  water,  in  such  proportion  that  at  least  £  of  the  total 
volume  consists  of  hydrochloric  acid  (sp.  gr,  1'12). 

The  excess  of  bichromate  is  found  by  a  standard  solution  of  pure  iron,  or 
of  double  iron  salt,  with  potassic  ferricyanide  as  indicator ;  the  quantity  of 
bichromate  reduced  is,  of  course,  the  measure  of  the  quantity  of  arsenious 
converted  into  arsenic  acid. 

1  c.c.  ^j-  bichromate =0-004 9 5  gin.  As203. 

In  cases  where  the  direct  titratiou  of  the  hydrochloric  acid  solution  cannot 
be  accomplished,  the  arsenious  acid  is  precipitated  with  H-S  (with  arsenates 
at  70°C.),  the  precipitate  well  washed,  the  filter  and  the  precipitate  placed  in 
a  stoppered  flask,  together  with  a  saturated  solution  of  mercuric  chloride  in 
hydrochloric  acid  of  1*12  sp.  gr.,  and  digested  at  a  gentle  heat  until  the 
precipitate  is  white,  then  water  added  in  such  proportion  that  not  less  than  £ 
of  the  volume  of  liquid  consists  of  concentrated  HC1 ;  •£$  bichromate  is  then 
added,  and  the  titration  with  standard  ferrous  solution  completed  as  usual. 

3.      Indirect    Estimation    by    Distilling    -with    Chromic    and 
Hydrochloric    Acids    (Bunsen). 

The  principle  of  this  very  exact  method  depends  upon  the  fact, 
that  when  potassic  bichromate  is  boiled  with  concentrated  hydro- 
chloric acid,  chlorine  is  liberated  in  the  proportion  of  3  eq.  to  1  eq. 
chromic  acid  (see  §  52.2). 

If,  however,  arsenious  acid  is  present,  but  not  in  excess,  the 
chlorine  evolved  is  not  in  the  proportion  mentioned  above,  but  so 
much  less  as  is  necessary  to  convert  the  arsenious  into  arsenic  acid. 

As203  +  4C1  +  2H20= As205  +  4HC1. 

Therefore  every  4  eq.  of  chlorine,  short  of  the  quantity  yielded 
when  bichromate  and  hydrochloric  acid  are  distilled  alone,  represent 
1  eq.  arsenious  acid.  The  operation  is  conducted  in  the  apparatus 
fig.  29  or  30. 

4.      By    Precipitation    as    TJranic    Ar senate    (Bodeker). 

The  arsenic  must  exist  in  the  state  of  arsenic  acid  (As205),  and  the  process 
is  in  all  respects  the  same  as  for  the  estimation  of  phosphoric  acid,  devised 
byNeubauer,  Pincus,  and  myself  (§  69).  The  strength  of  the  uranium 
solution  may  be  ascertained  and  fixed  by  pure  sodic  or  potassic  arsenate,  or 
by  means  of  a  weighed  quantity  of  pure  arsenious  acid  converted  into  arsenic 
acid  by  evaporation  with  strong  nitric  acid,  and  neutralizing  with  alkali,  then 


HUBERT 


§  43.  AKSENIC.  ]39 

dissolved  in  acetic  acid.  The  method  of  testing  is  precisely  the  same  as  with 
phosphoric  acid  ;  the  solution  of  uranium  should  be  titrated  upon  a  weighed 
amount  of  arsenical  compound,  bearing  in  mind  here,  as  in  the  case  of  P2O5, 
that  the  titration  must  take  place  under  precisely  similar  conditions  as  to 
quantity  of  liquid,  the  amount  of  sodic  acetate  and  acetic  acid  added,  and 
the  depth  of  colour  obtained  by  contact  of  the  fluid  under  titration  with  the 
yellow  prussiate  solution  (see  §  69). 

Eoam  (C.  N.  Ixi.  219),  who  lias  had  large  experience  in  the 
examination  of  arsenical  ores,  recommends  this  method  as  being 
rapid  and  accurate,  and  carries  it  out  as  follows  : — 

1  to  1'5  gm.  of  dried  and  powdered  ore  is  boiled  to  dryness  with  20 — 25 
c.c.  of  strong  nitric  acid  ;  when  cool  about  30  c.c.  of  30%  caustic  soda 
solution  is  added  and  boiled  for  a  few  minutes ;  then  diluted,  filtered  and 
made  up  to  250  c.c.  25  c.c.  of  the  liquid  is  acidified  with  a  solution 
containing  10  per  cent,  of  sodic  acetate  in  50  per  cent,  acetic  acid,  and 
heated  to  near  boiling,  then  titrated  with  the  standard  uranium  as  usual.  For 
this  latter,  the  same  authority  recommends  what  he  terms  a  fourth  normal 
solution  of  uranium,  containing  17'1  gm.  uranic  acetate,  and  15  c.c.  glacial 
acetic  acid  made  up  to  2  liters  with  water,  1  c.c.  being  equal  to  T25  m.gm. 
As.  But  if  the  method  has  to  be  considered  accurate,  this  suggestion  can 
scarcely  be  adopted,  since  the  uranic  acetate  of  commerce  is  of  indefinite 
hydration;  and  moreover,  to  insure  exactitude,  it  is  necessary  that  the 
titration  should  be  carried  out  with  the  same  proportions  of  saline  matters, 
acetic  acid,  etc.,  as  existed  in  originally  standardizing  the  uranium.  I  there- 
fore unhesitatingly  recommend  that  the  uranium  should  be  standardized 
with  a  known  weight  of  pure  arsenic  or  arsenate  in  the  presence  of  the  same 
proportions  of  sodic  hydra te.,  acetate  of  soda,  acetic  acid,  etc.,  as  will  actually 
be  used  in  the  analysis  of  an  ore.  The  method  may  be  used  for  all  ores 
which  can  be  attacked  by  nitric  acid.  It  is  also  available  for  iron  pyrites 
containing  tolerable  quantities  of  arsenic ;  the  ferric  arsenate  being  readily 
decomposed  by  excess  of  NaHO,  thus  allowing  the  ferric  hydrate  to  be 
filtered  off  free  from  As. 

The  solution  of  arsenic  acid  must  of  course  be  free  from  metals 
liable  to  give  a  colour  with  the  indicator  and  from  phosphates. 
Alkalies,  alkaline  earths,  and  zinc  are  of  no  consequence,  but  it  is 
advisable  to  add  nearly  the  required  volume  of  uranium  to  the 
liquid  before  heating.  The  arsenic  acid  must  be  separated  from 
all  bases  which  would  yield  compounds  insoluble  in  weak  acetic 
acid. 

The  arsenetted  hydrogen  evolved  from  Marsh's  apparatus  may 
be  passed  into  fuming  HN"03,  evaporated  to  dryness,  the  arsenic 
acid  dissolved  in  water  (antimony  if  present  is  insoluble),  then 
titrated  cautiously  with  uranium  in  presence  of  free  acetic  acid  and 
sodic  acetate  as  above  described. 


5.      By    Standard    Silver    as    Arsenate. 

The  principle  of  this  method  has  been  adopted  by  Pearce 
of  the  Colorado  Smelting  Company,  and  also  by  Me  Cay  (C.  N. 
xlviii.  7).  The  authors,  however,  differ  in  the  details  of  the 
process.  The  former  prefers  to  separate  the  arsenic  as  silver 


VOLUMETRIC   ANALYSIS.  §    43. 

arsenate,  and,  estimating  the  silver  so  combined,  thence  calculate 
the  arsenic.  The  latter  uses  a  known  excess  of  standard  silver, 
and  estimates  the  combined  silver  residually. 

Pearce's  Process. — The  finely-powdered  substance  for  analysis  is  mixed 
in  a  large  porcelain  crucible  with  from  six  to  ten  times  its  weight  of  a 
mixture  of  equal  parts  of  sodic  carbonate  and  potassic  nitrate.  The  mass  is 
then  heated  with  a  gradually  increasing  temperature  to  fusion  for  a  few- 
minutes,  allowed  to  cool,  and  the  soluble  portion  extracted  by  warming  with 
water  in  the  crucible,  and  filtering  from  the  insoluble  residue.  The  arsenic 
is  in  the  filtrate  as  alkaline  arsenate.  The  solution  is  acidified  with  nitric 
acid  and  boiled  to  expel  CO2  and  nitrous  fumes.  It  is  then  cooled  to  the 
ordinary  temperature,  and  almost  exactly  neutralized  as  follows :— Place  a 
small  piece  of  litmus  paper  in  the  liquid  :  it  should  show  an  acid  reaction. 
Now  gradually  add  strong  ammonia  till  the  litmus  turns  blue,  avoiding 
a  great  excess.  Again  make  slightly  acid  with  a  drop  or  two  of  strong  nitric 
acid  ;  and  then,  by  means  of  very  dilute  ammonia  and  nitric  acid,  added  drop 
by  drop,  bring  the  solution  to  such  a  condition  that  the  litmus  paper,  after 
having  previously  been  reddened,  will,  in  the  course  of  half  a  minute, 
begin  to  show  signs  of  alkalinity.  The  litmus  paper  may  now  be  removed 
and  washed,  and  the  solution,  if  tolerably  clear,  is  ready  for  the  addition  of 
silver  nitrate.  If  the  neutralization  has  caused  much  of  a  precipitate 
(alumina,  etc.),  it  is  best  to  filter  it  off  at  once,  to  render  the  subsequent 
filtration  and  washing  of  the  arsenate  of  silver  easier. 

A  solution  of  silver  nitrate  (neutral)  is  now  added  in  slight  excess ;  and 
after  stirring  a  moment,  to  partially  coagulate  the  precipitated  arsenate, 
which  is  of  a  brick-red  colour,  the  liquid  is  filtered,  and  the  precipitate 
washed  with  cold  water.  The  filtrate  is  then  tested  with  silver  and  dilute 
ammonia,  to  see  that  the  precipitation  is  complete. 

The  object  is  now  to  determine  the  amount  of  silver  in  the  precipitate, 
and  from  this  to  calculate  the  arsenic.  The  arsenate  of  silver  is  dissolved  on 
the  filter  with  dilute  nitric  acid  (which  leaves  undissolved  any  chloride 
of  silver),  and  the  filtrate  titrated,  after  the  addition  of  ferric  sulphate,  with 
ammonic  thiocyanate  (§  39). 

From  the  formula  3  Ag2O.As205,  648  parts  Ag=150  parts  As, 
or  Ag  :  As  =  108  :  25. 

Me  Cay's  Process. — The  preliminary  fusion  is  the  same  as  in  the 
former  method,  but  after  acidulating  with  nitric  acid  and  boiling 
off  CO2,  the  liquid  is  evaporated  to  dryness  and  heated  till  no  more 
acid  fumes  are  given  off.  The  residue  is  taken  up  with  water, 
filtered,  made  up  to  a  definite  volume,  and  the  arsenic  determined 
in  the  following  manner  : — 

The  solution  of  arsenic  acid  or  arsenate  is  heated  to  boiling,  and  excess  of 
standard  silver  nitrate  run  in ;  the  liquid  is  then  stirred  briskly  until  the 
precipitate  begins  to  settle  and  the  liquid  becomes  clear,  when  the  beaker  is 
to  be  removed  from  the  flame  and  left  to  cool  to  about  37°.  Dilute  ammonia 
is  now  carefully  added  until  a  cloudiness  ceases  to  form.  The  solution 
should  be  well  stirred  before  each  successive  addition,  so  as  to  obtain  a  clear 
liquid  in  order  to  observe  the  cloud  formation  more  distinctly.  The  silver 
arsenate  is  finally  filtered  off  and  well  washed ;  the  filtrate  is  acidulated  with 
nitric  acid ;  ferric  sulphate  added ;  and  the  silver  titrated  with  ammonic 
thiocyanate  according  to  Volhard's  method  (§  39).  The  amount  of  silver 
thus  found  deducted  from  the  quantity  taken  gives  the  amount  combined  with 
the  arsenic ;  and  from  this  datum  the  quantity  of  arsenic  present  is  calculated. 


§    44.  BARIUM.  141 

Of  these  two  methods  the  preference  must  be  given  to  the  first 
on  the  score  of  accuracy,  there  being  less  probability  of  error  from 
contaminating  substances  ;  both,  however,  are  available  for  technical 
purposes. 

Owing  to  the  large  amount  of  arsenate  of  silver  formed  from 
a  small  quantity  of  arsenic  (nearly  six  times  by  weight),  it  is 
not  at  all  necessary  or  even  desirable  to  work  with  large  amounts 
of  substance.  0'5  gm.  is  usually  sufficient  for  the  determination  of 
the  smallest  quantity  of  arsenic ;  and  where  the  percentage  is  high, 
as  little  as  O'l  gm.  may  be  taken  with  advantage.  The  method 
has  been  used  with  very  satisfactory  results  on  the  sulphide  of 
arsenic  obtained  in  the  ordinary  course  of  analysis. 

Substances  such  as  molybdic  and  phosphoric  acids,  which  may 
behave  similarly  to  arsenic  under  this  treatment,  interfere,  of  course, 
with  the  method.  Antimony,  by  forming  antimordate  of  sodium, 
remains  practically  insoluble  and  without  effect. 

The  method  has  been  used  by  Me  Cay  for  the  estimation  of 
arsenic  in  the  presence  of  alkaline  earths,  as  occurring  in  some 
minerals,  with  success. 


BARIUM. 

Ba=136-8. 

§  44.  IN  a  great  number  of  instances  the  estimation  of  barium 
is  simply  the  converse  of  the  process  for  sulphuric  acid  (§  73)r 
using  either  a  standard  solution  of  sulphuric  acid  or  a  neutral 
sulphate,  in  a  known  excess,  and  finding  the  amount  by  residual 
titration. 

When  barium  can  be  separated  as  carbonate,  the  estimation 
is  made  as  in  §  17. 

Precipitation  as  Baric  Chromate. — A  decinormal  solution  of 
bichromate  for  precipitation  purposes  must  differ  from  that  used 
for  oxidation  purposes.  In  the  present  case  the  solution  is  made 
by  dissolving  7 '37  gm.  of  pure  potassic  bichromate,  and  diluting 
to  1  liter. 

The  barium  compound,  which  may  contain  alkalies,  magnesia,  strontia, 
and  lime,  is  dissolved  in  a  good  quantity  of  water,  ammonia  free  from 
carbonate  added,  heated  to  60°  or  70°  C.,  and  the  standard  bichromate  added 
cautiously,  with  shaking,  so  long  as  the  yellow  precipitate  of  baric  chromate 
is  formed,  and  until  the  clear  supernatant  liquid  possesses  a  faint  yellow 
colour.  1  c.c.  *f  solution  =  0'00684  gm.  Ba. 

Titration  of  the  Precipitate  with.  Permanganate. — In  this  case  the 
precipitate  of  baric  chromate  is  well  washed,  transferred  to  a  flask,  and  mixed 
with  an  excess  of  double  iron  salt ;  the  amount  of  iron  oxidized  by  the 
chromic  acid  is  then  estimated  by  titration  with  permanganate ;  the  quantity 
of  iron  changed  to  the  ferric  state  multiplied  by  the  factor  0'8187  =  Ba. 


142  VOLUMETRIC  ANALYSIS.  §    45. 


BISMUTH. 

BI--208. 

§  45.  THE  estimation  of  this  metal  or  its  compounds  volumet- 
rically  has  occupied  the  attention  of  Pat  tins  on  Miiir,  to  whom 
we  are  indebted  for  several  methods  of  gaining  this  end.  Two  of 
the  best  are  given  here,  namely,  (1)  precipitation  of  the  metal 
as  basic  oxalate,  and  titration  with  permanganate  ;  (2)  precipitation 
as  phosphate  with  excess  of  standard  sodic  phosphate,  and  titration 
of  that  excess  by  standard  uranic  acetate. 

1.      Titration    as    Oxalate. 

Normal  bismuth  oxalate,  produced  by  adding  excess  of  oxalic 
acid  to  a  nitric  solution  of  the  metal  when  separated  by  filtration, 
and  boiled  with  successive  quantities  of  water  for  three  or  four 
times,  is  transformed  into  basic  oxalate.  The  method  of  titration 
is  as  follows  : — 

The  solution  containing  bismuth  must  be  free  from  hydrochloric  acid,  as 
the  basic  oxalate  is  readily  soluble  in  that  acid.  A  large  excess  of  nitric 
acid  must  also  be  avoided.  Oxalic  acid  must  be  added  in  considerable 
excess.  If  the  precipitate  be  thoroughly  shaken  up  with  the  liquid,  and  the 
vessel  be  then  set  aside,  the  precipitate  quickly  settles,  and  the  supernatant 
liquid  may  be  poured  off  through  a  filter  in  a  very  short  time.  If  the 
precipitate  be  boiled  for  five  or  ten  minutes  with  successive  quantities  of 
about  50  c.c.  of  water,  it  is  quickly  transformed  into  the  basic  salt.  So  soon 
as  the  supernatant  liquid  ceases  to  show  an  acid  reaction,  the  transformation 
is  complete.  It  is  well  to  employ  a  solution  of  permanganate  so  dilute,  that 
at  least  50  c.c.  are  required  for  the  titration  (^  strength  suffices) .  The  basic 
oxalate  may  be  dissolved  in  dilute  sulphuric  acid  in  place  of  hydrochloric ; 
it  is  more  soluble,  however,  in  the  latter  acid.  If  the  solution  contains  but 
little  hydrochloric  acid,  there  is  no  danger  of  chlorine  being  evolved  during 
the  process  of  titration. 

In  applying  this  process  to  the  estimation  of  bismuth  in  a  solution 
containing  other  metals,  it  is  necessary,  if  the  solution  contain  substances 
capable  of  acting  upon,  or  of  being  acted  on  by  permanganate,  to  separate 
the  bismuth  from  the  other  metals  present.  This  is  easily  done  by 
precipitating  in  a  partially  neutralized  solution  with  much  warm  water  and 
a  little  ammonic  chloride.  The  precipitate  must  be  dissolved  in  nitric  acid, 
and  the  liquid  boiled  down  once  or  twice  with  addition  of  the  same  acid  in 
order  to  expel  all  hydrochloric  acid,  before  precipitating  as  oxalate.  The 
liquid  should  contain  just  sufficient  nitric  acid  to  prevent  precipitation  of 
the  basic  nitrate  before  oxalic  acid  is  added.  1  molecule  oxalic  acid  corresponds 
to  1  atom  bismuth,  or  126  =  208. 

A  shorter  method,  based  on  the  same  reactions,  has  been  arranged 
by  Muir  and  Robbs  (J.  C.  S.  I.  xli.  1).  In  this  case,  however, 
the  double  oxalate  of  potassium  and  bismuth  is  the  compound 
obtained,  the  excess  of  oxalate  of  potash  being  determined 
residually.  Reis  (Bericlite,  xiv.  1172)  has  shown  that  when 
normal  potassic  oxalate  is  added  to  a  solution  of  bismuth  nearly 
free  from  mineral  acid,  but  containing  acetic  acid,  a  double  salt  of 


§    45.  BISMUTH.  143 

the  formula  Bi2  (C204)3,  K2C204  is  precipitated.  In  applying  this 
process  for  the  estimation  of  bismuth  in  mixtures,  it  is  necessary 
to  separate  the  metal  as  oxychloride,  and  that  it  should  be  obtained 
in  solution  as  nitrate  with  a  small  excess  of  nitric  acid.  This  is 
done  by  evaporating  off  the  greater  part  of  the  free  acid,  allowing 
just  sufficient  to  remain  that  the  bismuth  may  remain  in  solution 
while  hot.  A  large  excess  of  acetic  acid  is  then  added,  it  is  made 
up  to  a  definite  measure,  and  an  aliquot  portion  taken  for  titration. 
The  solution  of  normal  potassic  oxalate  standardized  by  perman- 
ganate must  not  be  added  in  great  excess.  It  is  well,  therefore,  to 
deliver  it  into  the  bismuth  liquid  from  a  burette  until  the 
precipitation  is  apparently  complete,  then  add  a  few  extra  c.c.,  and 
allow  to  remain  for  some  time  with  shaking.  It  is  then  filtered 
through  a  dry  filter,  a  measured  portion  taken,  and  the  residual 
oxalic  acid  found  by  permanganate. 


2.     Precipitation    as    Phosphate. 

The  necessary  standard  solutions  are — 

(a)  Standard  sodic  phosphate  containing  3 5 '8  gm.  per  liter. 
1  c.c.  =  0-0071  gm.  P205. 

(}))  Standard  uranic  acetate,  corresponding  volume  for  volume 
with  the  above,  when  titrated  with  an  approximately  equal  amount 
of  sodic  acetate  and  free  acetic  acid. 

Success  depends  very  much  upon  identity  of  conditions,  as  is 
explained  in  §  69. 

The  bismuth  to  be  estimated  must  be  dissolved  in  nitric  acid  ;  bases  other 
than  the  alkalies  and  alkaline  earths  must  be  absent.  The  absence  of  those 
acids  which  interfere  with  the  determination  of  phosphoric  acid  by  the 
uranium  process  (non-volatile,  and  reducing  organic  acids,  sulphuretted 
hydrogen,  hydriodic  acid,  etc.)  must  be  assured.  As  bismuth  is  readily 
separated  from  other  metals,  with  the  exception  of  antimony  and  tin,  by 
addition  of  much  warm  water  and  a  little  ammonic  chloride  to  feebly  acid 
solutions,  a  separation  of  the  bismuth  from  those  other  metals  which  are 
present  should  precede  the  process  of  estimation.  If  alkalies  or  alkaline 
earths  be  alone  present,  the  separation  may  be  dispensed  with.  The  pre- 
cipitated bismuth  salt  is  to  be  washed,  dissolved  in  a  little  strong  nitric  acid, 
and  the  solution  boiled  down  twice  with  addition  of  a  little  more  nitric  acid, 
in  order  to  remove  the  whole  of  the  hydrochloric  acid  present. 

Such  a  quantity  of  a  tolerably  concentrated  solution  of  sodic  acetate  is 
added  as  shall  insure  the  neutralization  of  the  nitric  acid,  and  therefore  the 
presence  in  the  liquid  of  free  acetic  acid.  If  a  precipitate  form,  a  further 
addition  of  sodic  acetate  must  be  made.  The  liquid  is  heated  to  boiling ;  a 
measured  volume  of  the  sodic  phosphate  solution  is  run  in ;  the  boiling  is 
continued  for  a  few  minutes  ;  the  liquid  is  passed  through  a  ribbed  filter,  the 
precipitate  being  washed  repeatedly  with  hot  water ;  and  the  excess  of  phos- 
phoric acid  is  determined  in  the  filtrate  by  titration  with  uranium.  If  the 
filtered  liquid  be  received  in  a  measuring  flask,  which  is  subsequently  filled 
to  the  mark  with  water,  and  if  the  inverted  uranium  method  be  then 
employed,  the  results  are  exceedingly  accurate.  This  method  is  especially  to 
be  recommended  in  the  estimation  of  somewhat  large  quantities  of  bismuth, 
since  it  is  possible  that  in  such  cases  a  large  amount  of  sodic  acetate  will 


144  VOLUMETRIC    ANALYSIS.  §    46. 

have  been  used,  which,  as  is  well  known,  has  a  considerable  disturbing  effect 
on  the  reaction  of  the  indicator. 

If  the  bismuth  solution  contain  a  large  excess  of  nitric  acid,  it  is  better  to 
neutralize  nearly  with  sodic  carbonate  before  adding  sodic  acetate  and  titrating. 

Fuller  details  of  both  the  above  processes  are  contained  in  /.  C.  S. 
1877  (p.  674)  and  1878  (p.  70). 

BROMINE. 

Br=80. 

§  46.  THIS  element,  or  its  imoxidized  compounds,  can  be 
estimated  precisely  in  the  same  way  as  chlorine  by  •£$  silver  solution 
(§  37),  or  alkalimetrically  as  in  §  28,  or  by  sulphocyanate  (§  39), 
but  these  methods  are  seldom  of  any  avail,  since  the  absence  of 
chlorine  or  its  combinations  is  a  necessary  condition  of  accuracy. 

Bromine  in  aqueous  solution,  or  as  gas,  may  be  estimated  by 
absorption  with  solution  of  potassic  iodide,  in  many  cases  by  mere 
digestion,  and  in  other  cases  by  distillation,  in  any  of  the  forms  of 
apparatus  given  in  §  35,  and  the  operation  is  carried  out  precisely 
as  for  chlorine  (§  50).  1  eq.  1  =  1  eq.  Br.  or  I  found  x  0'63  =  Br. 

A  process  for  the  estimation  of  bromine  in  presence  of  chlorine 
is  still  much  wanted  in  the  case  of  examining  kelp  liquors,  etc. 
Heine  (Journ.  f.  pract.  Cliem.  xxxvi.  184)  uses  a  colour  method 
in  which  the  bromine  is  liberated  by  free  chlorine,  absorbed  by 
ether,  and  the  colour  compared  with  an  ethereal  solution  of  bromine 
of  known  strength.  Fehling  states  that  with  care  the  process 
gives  fairly  accurate  results.  It  is  of  course  necessary  to  have  an 
approximate  knowledge  of  the  amount  of  bromine  present  in  any 
given  solution. 

Reimann  (AnnaL  d.  CJtem.  u.  Pliarm.  cxv.  140)  adopts  the 
following  method,  which  gives  tolerably  accurate  results,  but 
requires  skill  and  practice. 

The  neutral  bromine  solution  is  placed  in  a  stoppered  vessel, 
together  with  a  globule  of  chloroform  about  the  size  of  a  hazel  nut. 
Chlorine  water  of  known  strength  is  then  added  cautiously  from 
a  burette,  protected  from  bright  light,  in  such  a  way  as  to  insure 
first  the  liberation  of  the  bromine,  which  colours  the  chloroform 
orange  yellow ;  then  more  chlorine  water,  until  the  yellowish  white 
colour  of  chloride  of  bromine  occurs  (KBr  + 2Cl=KCl  +  BrCl). 

The  operation  may  be  assisted  by  making  a  weak  solution  of 
potassic  chromate,  of  the  same  colour  as  a  solution  of  chloride  of 
bromine  in  chloroform,  to  serve  as  a  standard  of  comparison. 

The  strength  of  the  chlorine  water  is  ascertained  by  potassic 
iodide  and  —5-  hyposulphite.  2  eq.  Cl=l  eq.  Br. 

In  examining  mother-liquors  containing  organic  matter,  they 
must  be  evaporated  to  dryness  in  presence  of  free  alkali,  ignited,, 
extracted  with  water;  then  neutralized  with  hydrochloric  acid 
before  titrating  as  above. 


§    46.  BROMINE.  145 

Cavazzi  (Gazz.  Cliim.  Ital.  xiii.  174)  gives  a  method  which 
answers  well  for  estimating  bromine  in  small  quantity,  when  mixed 
with  large  proportions  of  alkaline  chlorides.  It  is  based  on  the 
fact  that,  when  such  a  mixture  is  heated  to  100°  C.  with  baric 
peroxide  and  sulphuric  acid,  the  whole  of  the  bromine  is  liberated 
with  a  mere  trace  of  chlorine ;  the  bromine  so  evolved  is  absorbed 
in  any  convenient  apparatus,  such  as  fig.  29,  p.  117.  The  dis- 
tillation is  made  in  a  350  c.c.  flask  with  double-bored  stopper ;  one 
bore  contains  an  open  tube  reaching  to  the  bottom  of  the  flask,  the 
other  carries  the  delivery  tube  which  is  connected  with  the  (J  tubes. 
The  first  (J  tube  is  empty;  the  second  contains  20  c.c.  of  a 
standard  solution  of  arsenious  acid  in  hydrochloric  acid,  containing 
0-005  gin.  As203  in  each  c.c.,  and  is  connected  with  an  aspirator. 
The  apparatus  is  arranged  so  that  the  flask  and  empty  (J  tube  are 
immersed  in  boiling  water,  the  vapours  of  H202  are  thus  decomposed, 
and  the  stream  regulated  by  the  aspirator. 
The  requisites  used  by  the  author  are — 
Baric  peroxide,  containing  about  63%  BaO2. 
Dilute  sulphuric  acid  1  :  2. 

Arsenious  acid  dissolved  in  dilute  hydrochloric  acid,  5  gm.  of 
pure  As203  per  liter. 

Standard  permanganate,  3 '55  gm.  per  liter. 

It  was  found  that  the  relative  strengths  of  the  arsenic  and 
permanganate  solutions,  when  titrated  together,  diluted,  and  boiling, 
were,  18*2  c.c.  of  the  latter- to  20  c.c.  of  the  former.  Therefore 
1  c.c.  of  permanganate  by  calculation  =  0'00888  gm.  Br. 

The  author  found  that  treating  2  gm.  of  KC1  in  the  apparatus, 
without  bromine,  always  gave  a  faint  trace  of  Cl,  so  that  only 
18  c.c.  of  permanganate  were  required  for  the  20  c.c.  of  arsenic, 
instead  of  18 '2  c.c. ;  and  this  he  regards  as  a  constant  for  that 
quantity  of  material.  The  examples  of  analysis  with  from  0'05  to 
0'2  gm.  KBr,  and  all  with  the  correction  of  0'2  c.c.,  are  satisfactory. 
Norman  McCulloch  (C.  N.  Ix.  259)  has  described  a  method, 
devised  by  himself,  for  the  rapid  and  accurate  estimation  of  bromine, 
in  presence  of  iodine  or  chlorine,  in  any  of  the  ordinary  commercial 
forms  or  chemical  combinations,  free  from  oxidizing  and  reducing 
agents  and  metals  forming  bromides,  insoluble  in  hydrochloric 
acid.  The  author's  explanation  of  the  principles  upon  which 
the  method  is  based  is  complicated  and  voluminous,  for  which  the 
reader  is  referred  to  the  original  article.  I  have  not  been  able  to 
verify  the  method,  but  as  the  author  is  known  to  have  practical 
experience,  as  well  as  theoretical  knowledge,  a  short  summary  is 
given  here. 

The  requisites  described  by  the  author  are — 
Standard  permanganate,  31*9  grains  of  the  salt  in  10,000  grains 
of  water  (or  3*19  gm.  per  liter). 

Standard  potassic  iodide,  82'78  grains  of  KI  in  10,000  grains  of 
water  (or  8 '278  gm.  per  liter). 

L 


146  VOLUMETRIC  ANALYSIS.  §   46. 

The  solutions  should  agree  volume  for  volume,  but  it  is  preferable 
to  verify  them  by  dissolving  3-5  grains  of  iodine  in  caustic  soda, 
in  a  5-oz.  stoppered  bottle,  adding  HC1  in  good  excess,  cooling, 
then  adding  the  permanganate  from  a  burette,  until  nearly  colour- 
less. A  little  chloroform  as  indicator  is  then  added,  and  the 
permanganate  cautiously  run  in,  with  shaking,  until  the  violet 
colour  of  the  iodine  is  discharged,  owing  to  production  of  IC1, 
due  to  the  reaction  of  Cl  liberated  by  the  permanganate  from 
HC1. 

The  iodine  equivalent  of  the  permanganate  is  calculated  to 
bromine  by  the  factor  x  0*6713,  and  each  decem  of  permanganate 
should  represent  about  0*04  grain  Er  (or  each  c.c.  O004 
gm.  Br). 

The  other  reagents  are  purified  chloroform,  made  by  adding 
some  permanganate,  then  HC1  till  colour  is  discharged,  then  a  little 
KI  and  the  I  so  liberated  again  discharged  with  permanganate, 
finally  the  chloroform  is  washed  free  from  all  acid. 

A  three  per  cent  solution  of  hydrocyanic  acid,  made  by  decom- 
posing a  solution  of  pure  potassic  cyanide,  with  excess  of  HC1,  and 
adding  permanganate  till  a  faint  pink  colour  remains.  600  grains 
of  KCN  in  13  J  ounces  of  water  (or  40  gm.  in  400  c.c.)  with 
2J  ounces  of  HC1  (or  70  c.c.)  will  give  such  a  solution.  Owing  to 
its  poisonous  nature  great  caution  must  be  used  in  making  this 
solution,  and  to  avoid  as  much  as  possible  the  evolution  of  prussic 
acid  the  temperature  must  be  kept  down  by  ice,  or  a  freezing 
mixture  of  nitre  and  sal  ammoniac.  If  the  cyanide  contains,  as  is 
often  the  case,  some  alkaline  carbonate,  this  should  be  removed 
previously  by  Bad,  as  otherwise  CO2  will  be  liberated  and  a  loss 
of  HCN  occur,  finally  the  cool  solution  is  rendered  faintly  pink 
with  some  permanganate. 

Solution  of  manganous  chloride,  made  by  dissolving  half  a  pound 
of  MnCl2  +  4H20  in  4  oz.  of  warm  water  (or  500  gm.  in  250  c.c.). 
This  solution  is  used  to  prevent  the  liberation  of  free  chlorine 
from  the  HC1  in  the  analysis. 

The  Analysis :  The  weighed  bromide,  containing  from  1  to  3  grains  of 
Br  (0'05  to  0'15  gm.),  is  dissolved  in  half  an  ounce  (15  c.c.)  of  water  in  a  5  oz. 
stoppered  bottle,  and  about  an  ounce  (30  c.c.)  of  the  manganese  solution 
added ;  permanganate  is  then  run  in  excess  of  the  required  quantity,  and  the 
bottle  cooled  rapidly  to  50°  F.  (10°  C.)  by  ice  or  a  freezing  mixture.  When 
cooled,  the  bottle  is  shaken  by  a  rotary  motion,  and  about  half  an  ounce 
(15  c.c.)  of  moderately  strong  HC1  slowly  added,  with  motion  of  the  bottle 
to  dissolve  the  manganic  hydroxide,  3  to  6  dm.  (2 — 4  c.c.)  of  hydro- 
cyanic solution  are  then  delivered  in,  the  bottle  closed  and  returned  to  the 
cooling  mixture  for  about  half  an  hour.  The  liquid  is  then  titrated  with 
the  standard  potassic  iodide,  until  nearly  decolorized  from  the  decomposition 
of  the  manganic  chloride,  and  then  slightly  coloured  from  liberation  of  free  I. 
Lastly,  the  slight  excess  of  iodide  is  estimated  by  adding  a  little  chloroform, 
and  the  titration  finished  with  permanganate.  The  bromine  is  calculated  by 
taking  the  difference  between  the  amounts  of  bromine,  represented  by  total 
permanganate  and  iodide  used.  If  iodine  is  present  it  is  of  course  recorded 


§  47.  CADMIUM.  147 

as  bromine,  and  its  amount,  if  required,  must  be  ascertained  by  some  other 
method  capable  of  its  estimation  in  the  presence  of  bromine. 

The  author  gives  several  very  good  results  with  pure  sodic 
bromide,  an  example  of  which  may  be  given.  Each  measure  of 
permanganate  =  0-03 9 2  Br.  1*032  grain  Br  was  taken,  and  40'6 
measures  of  permanganate  with  14*3  measures  of  iodide  used,  then 
40-6  -  14-3  =  26-3  which  multiplied  by  0'0392  =  1-031  Br. 


CADMIUM. 
Cd- 111-6 

§  47.  THIS  metal  may  be  estimated,  as  is  the  case  with  many 
others,  by  precipitation  as  sulphide,  and  decomposing  the  sulphide 
with  a  ferric  salt,  the  iron  being  reduced  to  the  ferrous  state  in 
proportion  to  the  amount  of  sulphide  present. 

Follenius  has  found  that  when  cadmium  is  precipitated  as 
sulphide  in  acid  liquids,  the  precipitate  is  apt  to  be  contaminated 
with  salts  other  than  sulphide  to  a  small  extent.  The  separation 
as  sulphide  is  best  made  by  passing  H2S  into  the  hot  liquid  which 
contains  the  cadmium,  and  which  should  be  acidified  with  10  per 
cent,  of  concentrated  sulphuric  acid  by  volume.  From  hydrochloric 
acid  solutions  the  metal  is  only  completely  separated  by  IPS  when 
the  hot  solution  contains  not  more  than  5  per  cent,  of  acid  of 
sp.  gr.  I'll,  or  14  per  cent,  if  the  liquid  is  cold. 

Ferric  chloride  is  to  be  preferred  for  the  decomposition  of  the 
cadmium  sulphide,  and  the  titration  is  carried  out  precisely  as  in 
the  case  of  zinc  (§  78.2). 

P.  von  Berg  (Z.  a.  C.  xxvi.  23)  gives  a  good  technical  process 
for  the  estimation  of  either  cadmium  or  zinc  as  sulphides,  by 
means  of  iodine,  as  follows : — 

The  washed  sulphide  of  zinc  or  cadmium  is  allowed  to  drain  upon  the 
filter,  and  then  transferred,  together  with  the  filter,  to  a  stoppered  flask 
containing  800  c.c.  of  water  deprived  of  air  by  boiling  and  the  passage  of 
carbonic  acid  gas.  The  whole  is  well  shaken  to  break  up  the  precipitate  and 
bring  it  into  the  most  finely  divided  condition  possible,  so  that  the  sulphide 
may  not  be  protected  from  the  action  of  the  iodine  by  separated  sulphur. 
A  moderate  quantity  of  hydrochloric  acid  is  added,  there  being  no  necessity 
to  entirely  dissolve  the  sulphide,  and  then  an  excess  of  iodine  solution  of 
known  strength.  The  residual  free  iodine  is  then  titrated  with  thiosulphate 
without  loss  of  time.  The  whole  operation,  from  the  transference  of  the 
sulphide  to  the  flask  to  the  final  titration,  occupies  about  five  minutes,  and 
gives  results  varying  between  98' 8  and  100'2  per  cent.  The  reaction  proceeds 
according  to  the  equation,  ZnS+2HCl+2l=ZnCl2+2HI+S. 

Cadmium  may  also  be  estimated,  when  existing  as  sulphate  or 
nitrate,  by  precipitation  as  oxalate,  and  titration  of  the  washed 
precipitate  by  permanganate.  The  details  are  carried  out  precisely 
as  in  the  case  of  estimating  zinc  as  oxalate  (§  78). 

L  2 


148  VOLUMETRIC   ANALYSIS.  §    48. 

CALCIUM. 

Ca=40. 

1  c.c.  j^j-  permanganate          =  0-0028  gm.  CaO 

-  0-0050  gm.  CaCO3 
=  0-0086  gm.  CaSO4  +  2H20 
„      normal  oxalic  acid  =  0'0280  gm.  CaO 

Cryst.  oxalic  acid  x  0'444      =  CaO 

Double  iron  salt  x  0-07143  =  CaO 

§  48.  THE  estimation  of  calcium  alkalimetrically  lias  already  been 
given  (§  17),  but  that  method  is  of  limited  application,  unless  calcic 
oxalate,  in  which  form  Ca  is  generally  separated  from  other  bases, 
be  converted  into  carbonate  or  oxide  by  ignition,  and  thus 
determined  with  normal  •  nitric  acid  and  alkali.  This  and  the 
following  method  by  Hemp  el  are  as  exact  in  their  results  as  the 
determination  by  weight ;  and  where  a  series  of  estimations  have 
to  be  made,  the  method  is  very  convenient. 

Titration  with  Permanganate. — The  readiness  with  which  calcium 
can  be  separated  as  oxalate  facilitates  the  use  of  this  method,  so 
that  it  can  be  applied  successfully  in  a  great  variety  of  instances. 
It  is  not  necessary  here  to  enter  into  detail  as  to  the  method  of 
precipitation  ;  except  to  say,  that  it  may  occur  in  either  ammoniacal 
or  weak  acetic  acid  solution ;  and  that  it  is  absolutely  necessary  to 
remove  all  excess  of  ammonic  oxalate  from  the  precipitate  by 
washing  with  warm  water  previous  to  titration. 

"When  the  clean  precipitate  is  obtained,  a  hole  is  made  in  the  filter,  and 
the  bulk  of  the  precipitate  is  washed  through  the  funnel  into  a  flask ;  the 
filter  is  then  treated  with  small  quantities  of  hot  dilute  hydrochloric  acid, 
and  again  washed  into  the  flask.  Hydrochloric  acid  in  moderate  quantity 
may  be  safely  used  for  the  solution  of  the  oxalate,  since  there  is  not  the 
danger  of  liberating  free  chlorine  which  exists  in  the  case  of  iron  (Fleischer, 
Titrirmethode,  p.  76). 

When  the  precipitate  is  completely  dissolved,  the  solution  is  freely  diluted 
with  water,  and  further  acidified  with  sulphuric  acid,  warmed  to  70°  or  80°, 
and  the  standard  permanganate  cautiously  delivered  into  the  liquid  with 
constant  agitation  until  a  faint  permanent  pink  tinge  occurs,  precisely  as  in 
the  case  of  standardizing  permanganate  with  oxalic  acid  (§  30.2c). 

In  all  cases  where  a  clean  oxalate  precipitate  can  be  obtained, 
such  as  mineral  waters,  manures,  etc.,  very  exact  results  are  obtain- 
able ;  in  fact,  quite  as  accurate  as  by  the  gravimetric  method. 
Ample  testimony  on  this  point  is  given  by  Fresenius,  Mohr, 
Hempel,  and  others. 

Tucker  (Iron,  Nov.  16,  1878)  has  given  the  results  of  many 
experiments  made  by  him  upon  mixtures  of  Ca  with  abnormal 
proportions  of  iron,  magnesia,  alumina,  etc. ;  and  even  here  the 
numbers  obtained  did  not  vary  more  than  2  to  3  per  cent,  from  the 
truth.  In  the  case  of  large  proportions  of  these  substances  it  will 


§    49.  CALCIUM,    CERIUM,   CHLORINE.  149 

be  preferable  to  re-precipitate  the  oxalate,  so  as  to  free  it  from 
adhering  contaminations  previous  to  titration. 

Tucker  recommends  the  method  for  the  rapid  estimation  of  Ca 
in  furnace  slags,  etc.,  by  dissolving  in  aqua  regia,  without  filtering, 
precipitating  with  ammonic  oxalate,  and  then  filtering,  washing- 
well,  and  titrating  as  usual.  If  the  slag  contain  much  manganese 
or  iron  they  should  first  be  removed. 

indirect  Titration. — In  the  case  of  calcic  salts  soluble  in  water  and 
of  tolerably  pure  nature,  the  estimation  by  permanganate  can  be 
made  by  adding  to  the  solution  a  measured  excess  of  normal  oxalic 
acid,  neutralizing  with  ammonia  in  slight  excess,  and  heating  to 
boiling,  so  as  to  rapidly  separate  the  precipitate.  The  mixture  is 
then  cooled,  diluted  to  a  measured  volume,  filtered  through  a  dry 
filter,  and  an  aliquot  portion  titrated  with  permanganate  after 
acidifying  with  sulphuric  acid  as  usual.  A  great  variety  of  calcium 
salts  may  be  converted  into  oxalic  by  a  short  or  long  treatment 
with  oxalic  acid  or  ammonic  oxalate,  including  calcic  sulphate, 
phosphate,  tartrate,  citrate,  etc. 

CERIUM. 

Ce=  141-2. 

§  49.  THE  most  exact  method  of  estimating  this  metal  is  by 
precipitating  as  cerous  oxalate,  then  drying  the  precipitate,  and 
strongly  igniting  in  an  open  crucible,  so  as  to  convert  it  into  eerie 
oxide. 

Stolba  (Z.  a.  C.  xix.  194)  states  that  the  moist  oxalate  may  be 
titrated  precisely  as  in  the  case  of  calcic  oxalate  with  permanganate, 
and  with  accurate  results.  K"o  examples  or  details,  however,  are 
given. 

CHLORINE. 

01  =  35-37. 

1  c.c.  or  1  dm.  -^  silver  solution  =  O003537  gm.  or  0-03537  grn. 

Cl. 

=  0-005837  gm.  or  0'05837  grn. 
NaCl. 

§  50.  THE  powerful  affinity  existing  between  chlorine  and  silver 
in  solution,  and  the  ready  precipitation  of  the  resulting  chloride, 
seem  to  have  led  to  the  earliest  important  volumetric  process  in 
existence,  viz.,  the  assay  of  silver  by  the  wet  method  of  Gay 
Lussac.  The  details  of  the  process  are  more  particularly  described 
under  the  article  relating  to  the  assay  of  silver  (§  70);  the  deter- 
mination of  chlorine  is  just  the  converse  of  the  process  there 
described,  and  the  same  precautions,  and  to  a  certain  extent  the 
same  apparatus,  are  required. 


150  VOLUMETRIC  ANALYSIS.  §    50. 

The  solutions  required,  however,  are  systematic,  and  for  exactness 
and  convenient  dilution  are  of  decinormal  strength,  as  described  in 
§  37.  In  many  cases  it  is  advisable  to  possess  also  centinormal 
solutions,  made  by  diluting  100  c.c.  of  •£$  solution  to  1  liter. 


1.     Direct    Precipitation    with    g    Silver. 

Yery  weak  solutions  of  chlorides,  such  as  drinking  waters,  are  not  easily 
examined  for  chlorine  by  direct  precipitation,  unless  they  are  considerably 
concentrated  by  evaporation  previous  to  treatment,  owing  to  the  fact  that, 
unless  a  tolerable  quantity  of  chloride  can  be  formed,  it  will  not  collect 
together  and  separate  so  as  to  leave  the  liquid  clear  enough  to  tell  on  the 
addition  of  fresh  silver  whether  a  distinct  formation  of  chloride  occurs. 
The  best  effects  are  produced  when  the  mixture  contains  chlorine  equal  to 
from  H  to  2  gm.  of  salt  per  100  c.c.  ,  Should  the  proportion  be  much  less 
than  this,  the  difficulty  of  precipitation  may  be  overcome  by  adding  a 
quantity  of  freshly  precipitated  chloride,  made  by  mixing  equal  volumes  of 
TIT  salt  and  silver  solution,  shaking  vigorously,  pouring  off  the  clear  liquid, 
and  adding  the  chloride  to  the  mixture  under  titration.  The  best  vessel  to 
use  for  the  trial  is  a  well-stoppered  round  white  bottle,  holding  100  to  150 
c.c.,  and  fitting  into  a  paper  case,  so  as  to  prevent  access  of  strong  light 
during  the  analysis.  Supposing,  for  instance,  a  neutral  solution  of  potassic 
chloride  requires  titration,  20  or  30  c.c.  are  measured  into  the  shaking 
bottle,  a  few  drops  of  strong  nitric  acid  added  (free  acid  must  always  be 
present  in  direct  precipitation),  and  a  round  number  of  c.c.  of  silver  solution 
added  from  the  burette.  The  bottle  is  placed  in  its  case,  or  may  be  enveloped 
in  a  dark  cloth  and  vigorously  shaken  for  half  a  minute,  then  uncovered, 
and  gently  tapped  upon  a  table  or  book,  so  as  to  start  the  chloride  downward 
from  the  surface  of  the  liquid  where  it  often  swims.  A  quick  clarification 
indicates  excess  of  silver.  The  nearer  the  point  of  exact  counterbalance  the 
more  difficult  to  obtain  a  clear  solution  by  shaking,  but  a  little  practice  soon 
accustoms  the  eye  to  distinguish  the  faintest  precipitate. 

In  case  of  overstepping  the  balance  in  any  trial,  it  is  only 
necessary  to  add  to  the  liquid  under  titration  a  definite  volume  of 
Y^J-  salt  solution,  and  finish  the  titration  in  the  same  liquid, 
deducting,  of  course,  the  same  number  of  c.c.  of  silver  as  has  been 
added  of  salt  solution. 

Fuller  details  and  precautions  are  given  in  §  70. 


2.     Precipitation  by  JQ  Silver  in  Neutral  Solution  with  Chromate 
Indicator  (see  §  37,  2  b). 

3.     Titration  with  JQ  Sulphocyanate  (see  §  39). 

This  method  requires  some  little  practice  to  ensure  accurate 
results,  owing  to  the  fact  that  silver  chloride  slowly  decomposes 
silver  sulphocyanate. 

In  cases  where  the  amount  of  chlorine  is  approximately  known,  the 
material  is  dissolved  in  300  c.c.  or  so  of  water;  5  c.c.  of  ferric  indicator 
(§  39.3)  and  10  c.c.  of  nitric  acid  (§  39.4)  are  added ;  then  •&  silver  in 
moderate  excess  delivered  in  from  the  burette  with  constant  agitation.  The 


§    51.  CHLORINE.  151 

flask  is  then  brought  under  the  sulphocyanate  burette,  and  the  solution 
delivered  in  with  a  constant  gentle  movement  of  the  liquid  until  a  permanent 
light-brown  colour  appears.  The  immediate  mixing  of  the  solutions  is 
necessary  in  order  to  prevent  the  solvent  effect  of  the  concentrated  sulpho- 
cyanate. 

If  the  amount  of  chlorine  is  totally  unknown,  the  method  of 
procedure  is  as  follows  : — 

Dilute  the  solution  and  add  the  indicator  and  acid  as  above ;  but  during 
the  addition  of  the  silver  solution,  add  from  a  burette,  ready  filled  with 
sulphocyauate,  a  drop  or  two  from  time  to  time.  So  long  as  there  is  chlorine 
present  the  dark  red  colour  disappears  slowly  and  gradually ;  but  when  the 
colour  produced  by  a  fresh  drop  goes  off  at  once  on  agitation,  and  the  liquid 
appears  of  a  pure  milk  white,  the  silver  will  be  in  excess.  The  titration  is 
then  completed  as  above.  The  volume  of  sulphocyanate  used,  including  the 
amount  used  during  the  addition  of  the  silver,  deducted  from  the  T^  silver, 
will  show  the  volume  of  the  latter  necessary  for  precipitating  the  chlorine 
present. 


4.    By  Distillation  and  Titration  with.  Th.iosulph.ate  or  Arsenite. 

In  cases  where  chlorine  is  evolved  direct  in  the  gaseous  form  or 
as  the  representative  of  some  other  body  (see  §  35),  a  very  useful 
absorption  apparatus  is  shown  in  fig  29.  The  little  flask  a  is  used 
as  a  distilling  vessel,  connected  with  the  bulb  tubes  by  an  india- 
rubber  joint;*  the  stoppers  for  the  tubes  are  also  of  the  same 
material,  the  whole  of  which  should  be  cleansed  from  sulphur  by 
boiling  in  weak  alkali.  A  fragment  of  solid  magnesite  may  with 
advantage  be  added  to  the  acid  liquid  in  the  distilling  flask ;  in 
all  other  respects  the  process  is  conducted  exactly  as  is  described 
in  §  35. 

This  apparatus  is  equally  well  adapted  to  the  absorption  of 
ammonia  or  other  gases,  and  possesses  the  great  recommendation 
that  there  is  scarcely  a  possibility  of  regurgitation. 

Mohr's  apparatus  (fig.  30)  is  also  equally  serviceable  for  this 
method. 


CHLORINE    GAS    AND    BLEACHING    COMPOUNDS. 

1  c.c.  — j  arsenious  or  thiosulphate  solution  =  0*003537  gm.  Cl. 
1  liter  of  chlorine  at  0°C.,  and  760  m.m.,  weighs  3'167  gm. 

§  51.  CHLORINE  water  may  be  titrated  with  thiosulphate  by 
adding  a  measured  quantity  of  it  to  a  solution  of  potassic  iodide, 
then  delivering  the  thiosulphate  from  a  burette  till  the  colour  of 
the  free  iodine  has  disappeared ;  or  by  using  an  excess  of  the 
reducing  agent,  then  starch,  and  titrating  residually  with  •-$  iodine. 
When  arsenious  solution  is  used  for  titration,  the  chlorine  water  is 
delivered  into  a  solution  of  sodic  carbonate,  excess  of  arsenic 

••India-rubber  and  specially  vulcanized  rubber  is  open  to  some  objection  in  these 
analyses,  and  apparatus  is  now  readily  to  be  had  with  glass  connections. 


152  VOLUMETRIC  ANALYSIS.  §    51. 

added,  then  starch  and  —^  iodine  till  the  colour  appears,  or  the 
iodized  starch-paper  may  be  used  (§36). 

Bleaching-  Powder. — The  chief  substance  of  importance  among 
the  compounds  of  hypochlorous  acid  is  the  so-called  chloride  of 
lime.  The  estimation  of  the  free  chlorine  contained  in  it  presents 
no  difficulty  when  arsenious  solution  is  used  for  titration. 

Commercial  bleaching  powder  consists  of  a  mixture  in  variable 
proportions  of  calcic  hypochlorite  (the  true  bleaching  agent),  calcic 
chloride,  and  hydrate ;  and  in  some  cases  the  preparation  contains 
considerable  quantities  of  chlorate,  due  to  imperfect  manufacture. 
In  such  cases  Bun  sen's  method  of  analysis  gives  inaccurate 
results,  the  chlorate  being  recorded  as  a  bleaching  agent,  whereas 
it  is  not  so.  It  is  generally  valued  and  sold  in  this  country  by  its 
percentage  of  chlorine.  In  France  it  is  sold  by  degrees  calculated 
from  the  volume  of  gaseous  chlorine:  100°  French  =  31  '78  per 
cent.  English. 

1.      Titration    by    Arsenious    Solution. 

The  first  thing  to  be  done  in  determining  the  value  of  a  sample 
of  bleaching  powder  is  to  bring  it  into  solution,  which  is  best 
managed  as  follows : — 

The  sample  is  well  and  quickly  mixed,  and  7'17  gm.  weighed,  put  into  a 
mortar,  a  little  water  added,  and  the  mixture  rubbed  to  a  smooth  cream ; 
more  water  is  then  stirred  in  with  the  pestle,  allowed  to  settle  a  little  while, 
then  poured  off  into  a  liter  flask ;  the  sediment  again  rubbed  with  water, 
poured  off,  and  so  on  repeatedly,  until  the  whole  of  the  chloride  has  been 
conveyed  into  the  flask  without  loss,  and  the  mortar  washed  quite  clean. 
The  flask  is  then  filled  to  the  mark  with  water,  well  shaken,  and  50  c.c.  of 
the  milky  liquid  taken  out  with  a  pipette,  emptied  into  a  beaker,  and  the  -£& 
arsenious  solution  delivered  in  from  a  burette  until  a  drop  of  the  mixture 
taken  out  with  a  glass  rod,  and  brought  in  contact  with  the  prepared  starch- 
paper  (§  36)  gives  no  blue  stain. 

The  starch-paper  may  be  dispensed  with  by  adding  arsenious  solution  in 
excess,  then  starch,  and  titrating  residually  with  ^V  iodine  till  the  blue 
colour  appears.  The  number  of  c.c.  of  arsenic  used  shows  direct  percentage 
of  available  chlorine. 

A  more  rapid  method  can  be  adopted  in  cases  where  a  series  of  samples 
has  to  be  tested,  as  follows : — 4'95  gm.  of  pure  arsenious  acid  are  finely 
powdered  and  dissolved  by  the  aid  of  a  gentle  heat  in  about  15  c.c.  of 
glycerine,  then  diluted  with  water  to  1  liter;  25  c.c.  are  measured  into  a 
flask,  and  1  c.c.  of  indigo  solution  added.  The  turbid  solution  of  bleaching 
powder  is  poured  into  a  suitable  burette,  and  before  it  has  time  to  settle  is 
delivered  with  constant  shaking  into  the  blue  arsenious  solution  until  the 
colour  is  just  discharged;  the  percentage  of  chlorine  is  then  found  by  a  slight 
calculation. 

2.     Bun  sen's    Method. 

10  or  20  c.c.  of  the  chloride  of  lime  solution,  prepared  as  above,  are 
measured  into  a  beaker,  and  an  excess  of  solution  of  potassic  iodide  added ; 
the  mixture  is  then  diluted  somewhat,  acidified  with  hydrochloric  acid,  and 


§    51.  BLEACHING   POWDER.  153 

the  liberated  iodine  titrated  with  T^-  thiosulphate  and  starch  ;  1  eq.  iodine  so 
found  represents  1  eq.  chlorine. 

This  is  an  exceedingly  ready  method  of  estimating  chlorine,  hut  in  cases 
where  calcic  chlorate  is  present,  it  records  the  chlorine  in  it,  as  well  as  that 
existing  as  hypochlorite ;  but  as  the  chlorate  is  of  no  value  in  bleaching,  it 
is  always  preferable  to  analyze  bleaching  powder  by  means  of  arsenious 
solution.  The  amount  of  chlorate  can  always  be  found  by  taking  the 
difference  between  the  two  methods. 


3.     Gasometric    Process. 

This  method  has  been  devised  by  Lunge  (Bericlite  xix.  868, 
also  /.  S.  C.  I.  ix.  22)  and  is  both  accurate  and  rapid.  The 
instrument  used  for  the  analysis  is  preferably  the  new  gas 
volumeter,  with  patent  tap  and  bulb  (see  Part  VII.),  which  permits 
the  use  of  a  larger  weight  of  the  sample  than  the  ordinary  50  c.c. 
nitrometer.  In  both  instruments  for  this  class  of  analysis  ordinary 
tap  water  may  be  used,  instead  of  mercury,  with  equally  accurate 
results. 

The  reagent  used  for  the  decomposition  of  the  bleach  is 
hydrogen  peroxide,  and  the  reaction  is  CaOCl2  +  H202=CaCl2-f- 
H20  +  02.  Lunge's  directions  are  as  follows  : — 


1  fr- 


it is  not  necessary  to  know  the  exact  composition  of  the  hydrogen  peroxide, 
but  as  it  is  desirable  not  to  employ  too  large  an  excess  of  it  in  this  case,  it  is 
best  to  estimate  its  percentage  by  a  preliminary  test  occupying  but  a  few 
minutes,  in  which  a  certain  volume  of  H2O2  is  decomposed  by  an  excess  of 
bleach  solution  (the  inverse  of  the  titration  of  the  latter).  This  need  be 
done  only  quite  roughly.  For  the  analysis  of  chloride  of  lime  the  hydrogen 
peroxide  must  be  diluted  before  use  so  as  not  to  give  out  more  than  7  c.c.  of 
oxygen  per  c.c.,  and  it  must  be  made  alkaline  by  means  of  caustic  soda 
solution  up  to  the  point  where  a  flocculent  precipitate  appears.  The  alkaline 
reaction  ought  to  be  quite  distinct,  but  any  great  excess  of  alkali  should  be 
avoided.  It  is  not  necessary  to  shake  much,  and  the  reading  ought  to  be 
made  quickly,  say  five  minutes  after  mixing  the  liquids,  otherwise  the  results 
will  be  too  high  owing  to  the  gradual  evolution  of  more  oxygen  from  the 
alkaline  liquid.  It  might  be  thought  that  muddy  solutions,  such  as  are 
regularly  employed  in  testing  commercial  bleaching  powder,  would  yield  less 
reliable  results,  the  solid  matter  favouring  the  evolution  of  oxygen  from 
H2O2  otherwise  than  through  the  action  of  CaOCl2 ;  but  this  is  not  so ; 
muddy  solutions  can  be  tested  by  the  nitrometer  just  as  well  as  clear  bleach 
liquors,  provided  the  time  of  five  minutes  is  not  exceeded.  As  the  reaction 
does  not  produce  a  sensible  change  of  temperature,  that  time  will  quite 
suffice,  provided  that  the  operator  has  avoided  raising  the  temperature  of  the 
flask  in  manipulating  it,  which  he  can  do  by  handling  it  always  by  the  neck 
with  his  thumb  and  forefinger  only. 

In  order  to  find  the  percentage  of  available  chlorine  by  weight,  that  is, 
the  English  chlorometrical  degrees,  it  should  be  borne  in  mind  that  every 
c.c.  of  gas  evolved,  reduced  to  0°  and  760  mm.,  represents  0'003167  gm,  of 
chlorine.  Hence,  if  the  quantity  of  bleach  employed  is  =  1  gm.  (for 
instance,  by  dissolving  20  gm.  in  500  c.c.  of  water,  and  employing  25  c.c. 
of  the  solution  for  each  test),  each  c.c.  of  gas  is  =  0'3167  per  cent,  of 
available  chlorine  in  the  bleach.  This  involves  the  use  of  a  bulb  nitrometer 
holding  140  c.c.  If  only  a  50  c.c.  instrument  is  at  hand,  it  will  be  necessary 
to  take,  say,  5  c.c.  of  the  first-mentioned  bleach  solution,  in  which  case  every 


154  VOLUMETRIC  ANALYSIS.  §    52. 

c.c.  of  gas  represents  5x0*3167-=  1*58  per  cent,  of  chlorine.  The  most  con- 
venient way  is  to  dissolve  7*917  gm.  of  bleach  in  250  c.c.  of  water,  and 
employing  10  c.c.  of  the  solution  for  each  test,  when  each  c.c.  of  oxygen 
evolved  will  directly  indicate  1  per  cent,  of  available  chlorine,  and  a  50  c.c. 
nitrometer  should  be  used. 

The  general  method  of  manipulating  the  nitrometer  is  described 
in  Part  VII. 


CHLORATES,    IODATES,    AND    BROMATES. 

Chloric  anhydride,  C1205 =150*74.     lodic  anhydride,  I205=333. 
Eromic  anhydride,  Br205=239*5. 

The  compounds  of  chloric,  iodic,  and  bromic  anhydrides  may  all 
be  determined  by  distillation  or  digestion  with  excess  of  hydro- 
chloric acid;  with  chlorates  the  quantity  of  acid  must  be  con- 
siderably in  excess. 

In  each  case  1  eq.  of  the  respective  anhydrides  taken  as  mono- 
basic, or  their  compounds,  liberates  6  eq.  of  chlorine,  and  conse- 
quently 6  eq.  of  iodine  when  decomposed  in  the  digestion  flask. 
In  the  case  of  distillation,  however,  iodic  and  bromic  acids  only 
set  free  4  eq.  iodine,  while  iodous  and  bromous  chlorides  remain  in 
the  retort.  In  both  these  cases  digestion  is  preferable  to  distillation. 

Example :  0*2043  gin.  pure  potassic  chlorate,  equal  to  the  sixth  part  of 
ioooo  eq.,  was  decomposed  by  digestion  with  potassic  iodide  and  strong 
hydrochloric  acid  in  the  bottle  shown  in  fig.  28.  After  the  reaction  was 
complete,  and  the  bottle  cold,  the  stopper  was  removed,  and  the  contents 
washed  out  into  a  beaker,  starch  added,  and  103  c.c.  •&  thiosulphate  delivered 
in  from  the  burette ;  then  again  23*2  c.c.  of  T^-  iodine  solution,  to  reproduce 
the  blue  colour ;  this  latter  was  therefore  equal  to  2*32  c.c.  ^V  iodine,  which 
deducted  from  the  103  c.c.  thiosulphate  gave  100'68  c.c.,  which  multiplied  by 
the  factor  0'002043,  gave  0*2056  gm.  instead  of  0*2043  gm. 

CHROMIUM. 

Cr=52*4. 
1.      Reduction    by    Iron. 

§  52.  THE  estimation  of  chromates  is  very  simply  and  success- 
fully performed  by  the  aid  of  ferrous  sulphate,  being  the  converse 
of  the  process  devised  by  Penny  for  the  estimation  of  iron 
(see  §  33). 

The  best  plan  of  procedure  is  as  follows  : — 

A  very  small  beaker  or  other  convenient  vessel  is  partly  or  wholly  filled,  as 
may  be  requisite,  with  perfectly  dry  and  granular  double  sulphate  of  iron  and 
ammonia ;  the  exact  weight  then  taken  and  noted.  The  chromium  com- 
pound is  brought  into  solution,  not  too  dilute,  acidified  with  sulphuric  acid, 
and  small  quantities  of  the  iron  salt  added  from  time  to  time  with  a  dry  spoon, 
taking  care  that  none  is  spilled,  until  the  mixture  becomes  green,  and  the 
iron  is  in  excess,  best  known  by  a  small  drop  being  brought  in  contact  with  a 
drop  of  red  prussiate  of  potash  on  a  white  plate ;  if  a  blue  colour  appears  at 


§    52.  CHROMIUM.  155 

the  point  of  contact,  the  iron  is  in  excess.  It  is  necessary  to  estimate  this 
excess,  which  is  most  conveniently  done  by  T*^  bichromate  being  added  until 
the  blue  colour  produced  by  contact  with  the  red  prussiate  disappears.  The 
vessel  containing  the  iron  salt  is  again  weighed,  the  loss  noted ;  the  quantity 
of  the  salt  represented  by  the  T^  bichromate  deducted  from  it,  and  the 
remainder  multiplied  by  the  factor  required  by  the  substance  sought. 
A  freshly  made  standard  solution  of  iron  salt  may  be  used  in  place  of  the 
dry  salt. 

Example  :  0'5  gm.  pure  potassic  bichromate  was  taken  for  analysis,  and  to 
its  acid  solution  4' 15  gm.  double  iron  salt  added.  3*3  c.c.  of  T^-  bichromate 
were  required  to  oxidize  the  excess  of  iron  salt ;  it  was  found  that  0'7  gm.  of 
the  salt  =  17'85  c.c.  bichromate,  consequently  3'3  c.c.  of  the  latter  were  equal 
to  0'12985  gm.  iron  salt ;  this  deducted  from  the  quantity  originally  used 
left  4-02015  gm.,  which  multiplied  by  0'1255  gave  0'504  gm.  instead  of 
0'5  gm. 

In  the  case  of  lead  chromate  being  estimated  in  this  way,  it  is 
best  to  mix  both  the  chromate  and  the  iron  salt  together  in  a 
mortar,  rubbing  them  to  powder,  adding  hydrochloric  acid,  stirring 
well  together,  then  diluting  with  water  and  titrating  as  before. 
Where  pure  double  iron  salt  is  not  at  hand,  a  solution  of  iron  wire 
in  sulphuric  acid,  freshly  made,  and  of  ascertained  strength,  may  be 
used. 

2.   Estimation  of  Chromates  by  Distillation  with  Hydrochloric  Acid. 

When  chromates  are  boiled  with  an  excess  of  strong  hydrochloric 
acid  in  one  of  the  apparatus  (fig.  29  or  30),  every  1  eq.  of  chromic 
acid  liberates  3  eq.  chlorine.  For  instance,  with  potassic  bichromate 
the  reaction  may  be  expressed  as  follows — 

K2O207  +  14HC1=2KC1  +  Cr2Cl6  +  7H20  +  6C1. 

If  the  liberated  chlorine  is  conducted  into  a  solution  of  potassic 
iodide,  3  eq.  of  iodine  are  set  free,  arid  can  be  estimated  by  —^ 
arsenite  or  thiosulphate.  3  eq.  of  iodine  so  obtained =37 9 '5 
represent  1  eq.  chromic  acid =100 '40.  The  same  decomposition 
takes  place  by  mere  digestion,  as  described  in  §  35. 

3.      Chrome    Iron    Ore. 

The  ore  varies  in.  quality,  some  samples  being  very  rich,  while 
others  are  very  poor,  in  chromium.  In  all  cases  the  sample  is  to 
be  first  of  all  brought  into  very  fine  powder.  About  a  gram  is 
rubbed  tolerably  fine  in  a  steel  mortar,  then  finished  fractionally 
in  an  agate  mortar. 

Christomanos  recommends  that  the  coarse  powder  should  be 
ignited  for  a  short  time  on  platinum  previous  to  powdering  with 
the  agate  mortar ;  after  that  it  should  be  sifted  through  the  finest 
material  that  can  be  used,  and  the  coarser  particles  returned  to  the 
mortar  for  regrinding. 

Previous  to  analysis  it  should  be  again  ignited,  and  the  analysis 
made  on  the  dry  sample. 


156  VOLUMETEIC  ANALYSIS.  §    52. 

(a)  O'Neill's  Process. — The  very  finely  powdered  ore  is  fused  with 
ten  times  its  weight  of  potassic  bisulphate  for  twenty  minutes,  taking  care 
that  it  does  not  rise  over  the  edge  of  the  platinum  crucible ;  when  the  fusion 
is  complete,  the  molten  mass  is  caused  to  flow  over  the  sides  of  the  crucible, 
so  as  to  prevent  the  formation  of  a  solid  lump,  and  the  crucible  set  aside  to 
cool.     The  mass  is  transferred  to  a  porcelain  dish,  and  lixiviated  with  warm 
water  until  entirely  dissolved  (no  black  residue  must  occur,  otherwise  the 
ore  is  not  completely  decomposed)  ;  sodic  carbonate  is  then  added  to  the 
liquid  until  it  is  strongly  alkaline ;  it  is  then  brought  on  a  filter,  washed 
slightly,  and  the    filter  dried.      When  perfectly  dry,   the    precipitate  is 
detached  from  the  filter  as  much  as  possible ;  the  filter  burned  separately  ; 
the  ashes  and  precipitate  mixed  with  about  twelve  times  the  weight  of  the 
original  ore,  of  a  mixture  of  two  parts  potassic  chlorate  and  three  parts 
sodic  carbonate,  and  fused  in  a  platinum  crucible  for  twenty  minutes  or  so ; 
the  resulting  mass  is  then  treated  with  boiling  water,  filtered,  and  the  filtrate 
titrated  for  chromic  acid  as  in  §  52.1. 

The  ferric  oxide  remaining  on  the  filter  is  titrated,  if  required, 
by  any  of  the  methods  described  in  §§  59  and  60. 

(b)  Britten's  Process. — Reduce  the  mineral  to  the  finest  state  of 
division  possible  in  an  agate  mortar.     "Weigh  oif  0*5'  gin.,  and  add  to  it 
4  gm.  of  flux,  previously  prepared,  composed  of  one  part  potassic  chlorate 
and  three  parts  soda-lime ;  thoroughly  mix  the  mass  by  triturating  in  a 
porcelain  mortar,  and  then  ignite  in  a  covered  platinum  crucible  at  a  bright- 
red  heat  for  an  hour  and  a  half  or  more.     20  minutes  is  sufficient  with  the 
gas  blowpipe.     The  mass  will  not  fuse,  but  when  cold  can  be  turned  out  of 
the  crucible  by  a  few  gentle  taps,  leaving  the  interior  of  the  vessel  clean 
and  bright.     Triturate  in  the  mortar  again  and  turn  the  powder  into  a  tall 
4-oz.  beaker,  and  add  about  20  c.c.  of  hot  water,  and  boil  for  two  or  three 
minutes;    when  cold,  add  15  c.c.  of  HC1,  and  stir  with  a  glass  rod,  till 
the  solid  matter,  with  the  exception  probably  of  a  little  silica  in   flakes, 
becomes  dissolved.     Both  the  iron  and  chromium  will  then  be  in  the  highest 
state  of  oxidation — Fe2O3  and  Cr2O3.    Pour  the  fluid  into  a  white  porcelain 
dish  of  about  20-oz.  capacity,  and  dilute  with  washings  of  the  beaker  to 
about  3  oz.     Immediately  after,  also,  add  cautiously  1  gm.  of  metallic  iron 
of  known  purity,  or  an  equivalent  quantity  of  double  iron  salt,  previously 
dissolved  in  dilute  sulphuric  acid,  and  further  dilute  with  cold  water  to 
about  5  oz.,  to  make  up  the  volume  in  the  dish  to  about  8  oz.,  then  titrate 
with  T^-  permanganate  the  amount    of    ferrous    oxide    remaining.     The 
difference  between  the  amount  of  iron  found  and  of  the  iron  weighed  will 
be  the  amount  oxidized  to  sesquioxide  by  the  chromic  acid.     Every  one  part 
so  oxidized  will  represent  0'320  of  Cr  or  0'4663  of  sesquioxide,  Cr2O3,  in 
which  last  condition  the  substance  usually  exists  in  the  ore. 

If  the  amount  of  iron  only  in  the  ore  is  to  be  determined,  the  process  is 
still  shorter.  After  the  fluxed  mineral  has  been  ignited  and  reduced  to 
powder,  as  already  directed,  dissolve  it  by  adding  first,  10  c.c.  of  hot  water 
and  applying  a  gentle  heat,  and  then  15  c.c.  of  HC1,  continuing  the  heat  to 
incipient  boiling  till  complete  decomposition  has  been  effected;  cool  by 
immersing  the  tube  in  a  bath  of  cold  water,  add  pieces  of  pure  metallic  zinc 
sufficient  to  bring  the  iron  to  the  condition  of  protoxide  and  the  chromium 
to  sesquioxide,  and  apply  heat  till  small  bubbles  of  hydrogen  cease,  and  the 
zinc  has  become  quite  dissolved ;  then  nearly  fill  the  tube  with  cold  water, 
acidulated  with  one-tenth  of  sulphuric  acid,  and  pour  the  contents  into  the 
porcelain  dish,  add  cold  water  to  make  up  the  volume  to  about  8  oz.,  and 
complete  the  operation  with  standard  permanganate  or  bichromate. 

(c)     Sell's  Process. — This  method  is  described  in  J.  C.  S.  1879 


§    53.  COBALT.  157 

(p.  292),  and  is  carried  out  by  first  fusing  the  finely  ground  ore 
with  a  mixture  of  sodic  bisulphate  and  fluoride  in  the  proportion 
of  1  moL  bisulphate,  and  2  mol.  fluoride,  and  subsequent 
titration  of  the  chromic  acid  by  standard  thiosulphate  and  iodine. 

Prom  O'l  to  0'5  gm.  of  the  ore  is  placed  on  the  top  of  ten  times  its  weight 
of  the  above-mentioned  mixture  in  a  large  platinum  crucible,  and  ignited  for 
fifteen  minutes ;  an  equal  weight  of  sodic  bisulphate  is  then  added  and  well 
incorporated  by  fusion,  and  stirring  with  a  platinum  wire ;  then  a  further 
like  quantity  of  bisulphate  added  in  the  same  way.  When  complete 
decomposition  has  occurred,  the  mass  is  boiled  with  water  acidulated  with 
sulphuric  acid,  and  the  solution  diluted  to  a  definite  volume  according  to  the 
quantity  of  ore  originally  taken. 

To  insure  the  oxidation  of  all  the  chromium  and  iron  previous  to  titration, 
a  portion,  or  the  whole,  of  the  solution  is  heated  to  boiling,  and  permanganate 
added  until  a  permanent  red  colour  occurs.  Sodic  carbonate  is  then  added 
in  slight  excess,  and  sufficient  alcohol  to  destroy  the  excess  of  permanganate  ; 
the  manganese  precipitate  is  then  filtered  off,  and  the  clear  solution  titrated 
with  ^  thiosulphate  and  iodine. 

The  author  states  that  the  analysis  of  an  ore  by  this  method 
may  be  accomplished  in  one  hour  and  a  half. 

For  the  oxidation  of  salts  of  chromium,  the  same  authority 
recommends  boiling  with  potash  or  sodic  carbonate,  to  which 
a  small  quantity  of  hydrogen  peroxide  is  added  for  15  minutes. 

For  the  preliminary  fusion  and  oxidation  of  chrome  iron  ore, 
Dittmar  recommends  a  mixture  of  two  parts  borax  glass,  and  one 
and  a  half  part  each  of  sodic  and  potassic  carbonate.  These  are 
fused  together  in  a  platinum  crucible  until  all  effervescence  ceases, 
then  poured  out  into  a  large  platinum  basin  or  upon  a  clean  iron 
plate  to  cool,  broken  up,  and  preserved  for  use. 

Ten  parts  of  this  mixture  is  used  for  one  part  of  chrome  ore, 
and  the  fusion  made  in  a  platinum  crucible,  closed  for  the  first  five 
minutes,  then  opened  for  about  forty  minutes,  frequently  stirring 
with  a  platinum  wire,  and  using  a  powerful  Buns  en  flame. 

The  gas  blowpipe  hastens  this  method  considerably. 


COBALT. 

Co  =  59. 
Estimation  by  Mercuric   Oxide  and  Permanganate   (Winkler). 

§  53.  IF  an  aqueous  solution  of  cobaltous  chloride  or  sulphate  be 
treated  with  moist  finely  divided  mercuric  oxide,  no  decomposition 
ensues,  but  on  the  addition  of  permanganate  to  the  mixture, 
hydrated  cobaltic  and  manganic  oxides  are  precipitated.  It  is 
probable  that  no  definite  formula  can  be  given  for  the  reaction, 
and  therefore  practically  the  working  effect  of  the  permanganate  is 
best  established  by  a  standard  solution  of  cobalt  of  known  strength, 
say  metallic  cobalt  dissolved  as  chloride,  or  neutral  cobaltous 
sulphate. 


158  VOLUMETRIC  ANALYSIS.  §    53. 

The  Analysis :  The  solution,  free  from  any  great  excess  of  acid,  is  placed 
in  a  flask,  diluted  to  about  200  c.c.,  and  a  tolerable  quantity  of  moist  mer- 
quric  oxide  (precipitated  from  the  nitrate  or  perchloride  by  alkali  and  washed) 
added.  Permanganate  from  a  burette  is  then  slowly  added  to  the  cold  solution 
with  constant  shaking  until  the  rose  colour  appears  in  the  clear  liquid  above 
the  bulky  brownish  precipitate. 

The  appearance  of  the  mixture  is  somewhat  puzzling  at  the 
beginning,  but  as  more  permanganate  is  added  the  precipitate 
settles  more  freely,  and  the  end  as  it  approaches  is  very  easily 
distinguished.  The  final  ending  is  when  the  rose  colour  is 
persistent  for  a  minute  or  two;  subsequent  bleaching  must  not 
be  regarded. 

The  actual  decomposition  as  between  cobaltous  sulphate  and 
permanganate  may  be  formulated  thus — 

GCoSO4  +  5H20  +  2MnK04  =  K2S04  +  5H2S04  +  3Co203  +  2Mn02 

but  as  this  exact  decomposition  cannot  be  depended  upon  in  all  the 
mixtures  occurring,  it  is  not  possible  to  accept  systematic  numbers 
calculated  from  normal  solutions. 

Solutions  containing  manganese,  phosphorus,  arsenic,  active 
chlorine  or  oxygen  compounds,  or  organic  matter,  cannot  be  used 
in  this  estimation;  moderate  quantities  of  nickel  are  of  no 
consequence. 

Norman  McCulloch  (C.  N.  lix.  51)  has  proved  that  cobaltic 
oxide,  as  cobalticyanide,  is  a  stable  compound,  and  makes  use  of 
this  fact  to  establish  a  process  which  gives  very  good  results,  by 
conversion  of  cobaltocyanide  to  the  higher  state  of  oxidation,  the 
estimation  of  the  oxygen  being  the  measure  of  the  cobalt  itself. 
The  method  is  exact  in  the  presence  of  nickel,  manganese,  lead, 
arsenic,  zinc,  antimony,  uranium,  etc.,  but  not  in  that  of  iron  or 
copper. 

The  standard  solutions  required  are  the  ordinary  ~  potassic 
bichromate,  1  c.c.  of  which  represents  0*0059  gm.  or  1  dm.  0'059 
grn.  of  Co,  and  an  acid  solution  of  ammonio-ferrous  sulphate, 
whose  strength  is  known  by  titration  with  the  bichromate.  There 
is  also  required  a  5  per  cent,  solution  of  pure  potassic  cyanide,  and 
a  solution  of  nickel  sulphate. 

The  apparatus  required  may  be  simply  a  12-oz.  flask,  fitted  with 
two-hole  stopper,  one  for  a  thistle  funnel  and  the  other  as  an 
escape  for  vapour.  The  mouth  of  the  funnel  should  be  somewhat 
constricted,  and  the  lower  end  must  dip  beneath  the  surface  of  the 
liquid  in  the  flask. 

The  Analysis  :  The  standard  bichromate  and  cyanide  solutions  are  conveyed 
in  their  proper  quantities  to  the  flask  above  described,  a  few  drops  of  ammonia 
added  for  subsequent  neutralization  of  any  free  acid  in  solution  to  be  tested, 
and  the  whole  diluied,  if  necessary,  to  a  convenient  bulk  with  water. 

The  amount  of  bichromate  taken  need  not  greatly  exceed  the  theoretical 
requirement  for  the  greatest  probable  quantity  of  cobalt  to  be  estimated,  but, 


§    53.  COBALT.  159 

with  the  cyanide,  an  allowance  is  made  also  for  the  conversion  to  soluble 
double  cyanides  of  such  other  metals  as  may  be  present.  ^ 

The  cork  and  thistle-funnel  are  now  placed  in  position,  and  the  solution 
boiled  to  expel  air  from  the  flask.  The  hot  solution  to  be  tested,  of  con- 
venient bulk  and  not  too  acid,  and  free,  of  course,  from  oxidizing  or  reducing 
constituents,  is  now  added,  and  the  ensuing  reaction  is  instantaneously 
complete. 

After  this  stage  the  continued  use  of  the  cork  and  thistle-funnel  is 
necessary  only  in  presence  of  manganese. 

The  contents  of  the  flask  are  now  cautiously  treated  with  excess  of  a 
moderately  warm  concentrated  solution  of  ammonic  chloride,  and  the 
ebullition  sustained  for  about  ten  minutes  longer  to  expel  volatile  cyanide 
(an  operation  conducted  in  acid  chamber  or  in  a  draught  of  air  to  carry  off 
poisonous  fumes). 

It  now  remains,  preceding  the  estimation  of  non-reduced  chromic  acid 
with  ferrous  salt,  to  throw  down  soluble  cobaltocyanide  and  decompose 
potassium-nickel  cyanide  by  the  addition  of  nickel  sulphate.  This  is  to 
prevent  the  subsequent  formation  of  ferrous  cobaltocyanide  and  double 
cyanide  of  iron  and  nickel  respectively — compounds  difficultly  soluble  in 
dilute  acid — and,  consequently,  low  results.  To  effect  the  above  precipitation, 
a  weight  of  nickel  is  required  at  least  equal  to  that  of  the  nickel  and  cobalt 
existing  in  the  contents  of  the  flask,  but  if  such  acids  as  arsenic  and  phosphoric 
are  present  more  is  needed,  as  their  precipitation  is  involved.  Simply,  the 
solution  of  nickel  is  added  until  no  further  precipitate  is  formed,  or  until  the 
precipitate  settles  in  a  peculiar  manner,  to  be  known  by  experience ;  great 
excess  of  nickel  is  thus  avoided,  which  would  tend  to  interfere  with  the 
ferricyanide  reaction  in  the  subsequent  operation. 

The  contents  of  the  flask  are  now  poured  into  excess  of  a  hot  aqueous 
solution  of  standard  ferrous  salt  contained  in  a  basin,  acidified  with  a  few 
drops  of  hydrochloric  acid,  and  titrated  with  bichromate  in  usual  way. 

The  cobalt  is  calculated  by  multiplying  the  difference  between  the  number 
of  c.c.  or  dm.  of  bichromate  taken  at  the  outset  of  the  estimation  and  that 
found  at  the  completion  by  0'0059  or  0'059  respectively,  and  correcting  this 
by  a  slight  allowance  for  reducing  action  of  the  potassic  cyanide  and  its 
impurities  on  the  chromate.  In  the  author's  case  this  correction  was  taken 
from  experiment,  and  it  was  deemed  sufficiently  near  to  accept  the  reducing 
action  of  the  cyanide  as  simply  proportionate  to  the  quantity  of  this  reagent 
used  in  the  estimation,  although  it  is  not  altogether  independent  of  the 
proportion  and  amount  of  the  bichromate,  the  degree  of  dilution,  length  of 
time  of  boiling,  etc.  The  result  showed  that  100  dm.  of  the  bichromate  boiled 
for  a  few  minutes  with  its  own  bulk  of  the  cyanide,  and  then  for  about  ten 
minutes  more  with  addition  of  excess  of  ammonic  chloride,  lost  in  value  to 
the  extent  of  about  one  decem,  which  was  deducted  from  the  amount  of 
bichromate  reduced  by  the  cobaltocyanide  in  such  estimations,  using  the 
above  bulk  of  cyanide,  a  fifth  of  this  for  25  or  30  dm.,  and  so  on.  It  is,  of 
course,  advisable,  where  the  highest  accuracy  is  desired,  to  determine  the 
necessary  correction  by  a  blank  experiment,  and  duplicating  also  the 
approximate  quantity  of  cobalt. 

It  is  best  to  separate  iron  as  well  as  copper,  and  in  the  case  of  a  cobalt  ore 
the  author  would  dissolve  the  sample  in  aqua-regia,  and  evaporate  to  dryness. 
The  nitric  acid  would  then  be  destroyed  by  two  or  three  evaporations  to 
dryness  with  hydrochloric  acid,  and  the  copper  precipitated  from  the  solution 
of  the  residue  by  sulphuretted  hydrogen.  In  the  filtrate  from  sulphide  the 
iron  would  be  separated  by  the  acetate  of  soda  method,  and  the  iron 
precipitate  re-dissolved  and  re-precipitated  in  a  similar  way  to  separate  any 
small  portion  of  cobalt.  The  combined  filtrates  from  the  acetate  precipitates 
would  be  evaporated  to  convenient  bulk,  and  the  excess  of  acid  neutralized 
by  caustic  or  carbonated  soda.  The  solution  so  obtained  would  then  be  added 
to  suitable  amounts  of  bichromate  and  cyanide,  as  described  above. 


160  VOLUMETRIC   ANALYSIS.  §    54 

Examples :  I1 14  grain  Co  taken  and  25*4  dm.  respectively  of  bichromate 
and  cyanide  used.  The  volume  of  bichromate  reduced,  allowing  for  the 
correction,  was  19'2  dm.  =  1*13  grn.  Co.  Again,  T14  Co  and  2'28  Ni  taken, 
25  c.c.  of  bichromate  and  50  c.c.  of  cyanide  used,  the  volume  of  the  former 
reduced  was  19'1  dm.  =  l'12  grn.  Co.  Equally  good  results  were  obtained 
with  mixtures  of  manganese',  lead,  arsenic,  etc. 


COPPER. 

Cu  =  63. 

Factors. 

1  c.c.  TNQ  solution  =  0-0063  gin.  Cu. 
Iron  x  1-1 25         =  Cu. 
Double  Iron  Salt  x  0-1607  =  Cu. 

1.    Reduction  by  Grape  Sugar  and  subsequent  titration  with  Ferric 
Chloride  and  Permanganate  (Schwarz). 

§  54.  THIS  process  is  based  upon  the  fact  that  grape  sugar 
precipitates  cuprous  oxide  from  an  alkaline  solution  of  the  metal 
containing  tartaric  acid  ;  the  oxide  so  obtained  is  collected  and 
mixed  with  ferric  chloride  and  hydrochloric  acid.  The  result  is 
the  following  decomposition  : — 

Cu20  +  Fe2Cl6  +  2HC1  =  2CuCl2  +  2FeCl2  +  H20. 

Each  equivalent  of  copper  reduces  one  equivalent  of  ferric  to  ferrous 
chloride,  which  is  estimated  by  permanganate  with  due  precaution. 
The  iron  so  obtained  is  calculated  into  copper  by  the  requisite  factor. 

The  Analysis :  The  weighed  substance  is  brought  into  solution  by  nitric 
or  sulphuric  acid  or  water,  in  a  porcelain  dish  or  flask,  and  most  of  the  acid 
in  excess  saturated  with  sodic  carbonate;  neutral  potassic  tartrate  is  then 
added  in  not  too  large  quantity,  and  the  precipitate  so  produced  dissolved  to 
a.  clear  blue  fluid  by  adding  caustic  potash  or  soda  in  excess ;  the  vessel  is 
next  heated  cautiously  to  about  50°  C.  in  the  water  bath,  and  sufficient 
grape  sugar  added  to  precipitate  the  copper  present ;  the  heating  is  continued 
until  the  precipitate  is  of  a  bright  red  colour,  and  the  upper  liquid  is 
brownish  at  the  edges  from  the  action  of  the  alkali  on  the  sugar :  the  heat 
must  never  exceed  90°  C.  "When  the  mixture  has  somewhat  cleared,  the 
upper  fluid  is  poured  through  a  moistened  filter,  and  afterwards  the  precipitate 
brought  on  the  same,  and  washed  with  hot  water  till  thoroughly  clean ;  the 
precipitate  which  may  adhere  to  the  dish  or  flask  is  well  washed,  and  the 
filter  containing  the  bulk  of  the  protoxide  put  with  it,  and  an  excess  of 
solution  of  ferric  chloride  (free  from  nitric  acid  or  free  chlorine)  added, 
together  with  a  little  sulphuric  acid ;  the  whole  is  then  warmed  and  stirred 
until  the  cuprous  chloride  is  all  dissolved.  It  is  then  filtered  into  a  good- 
sized  flask,  the  old  and  new  filters  being  both  well  washed  with  hot  water,  to 
which  at  first  a  little  free  sulphuric  acid  should  be  added,  in  order  to  be 
certain  of  dissolving  all  the  oxide  in  the  folds  of  the  paper.  The  entire 
solution  is  then  titrated  with  permanganate  in  the  usual  way;  Bichromate 
may  also  be  used,  but  the  end  of  the  reaction  is  not  so  distinct  as  usual,  from 
the  turbidity  produced  by  the  presence  of  copper. 


§  54  COPPEK.  161 

2.      Reduction    by    Zinc    and    subsequent    titration    -with    Ferric 
Chloride    and    Permanganate    (Fleitmann). 

The  metallic  solution,  free  from  nitric  acid,  bismuth,  or  lead,  is 
precipitated  with  clean  sticks  of  pure  zinc ;  the  copper  collected, 
washed,  and  dissolved  in  a  mixture  of  ferric  chloride  and  hydro- 
chloric acid :  a  little  soclic  carbonate  may  be  added  to  expel  the 
atmospheric  air.  The  reaction  is — 

Cu  +  Fe2Cl6=CuCl2  +  2FeCl2. 

When  the  copper  is  all  dissolved,  the  solution  is  diluted  and 
titrated  with  permanganate;  56  Fe=31'5  Cu. 

If  the  original  solution  contains  nitric  acid,  bismuth,  or  lead, 
the  decomposition  by  zinc  must  take  place  in  an  ammoniacal 
solution,  from  which  the  precipitates  of  either  of  the  above  metals 
have  been  removed  by  filtration ;  the  zinc  must  in  this  case  be 
iinely  divided  and  the  mixture  warmed.  The  copper  is  all 
precipitated  when  the  colour  of  the  solution  has  disappeared.  It 
is  washed  first  with  hot  water,  then  with  weak  HC1  and  water  to 
remove  the  zinc,  again  with  water,  and  then  dissolved  in  the  acid 
and  ferric  chloride  as  before. 

3.      Estimation    as    Cuprous    Iodide    (E.     O.    Brown). 

This  process  is  based  on  the  fact  that  when  potassic  iodide  is 
mixed  with  a  salt  of  copper  in  acid  solution,  cuprous  iodide  is 
precipitated  as  a  dirty  white  powder,  and  iodine  set  free.  If  the 
latter  is  then  immediately  titrated  with  thiosulphate  and  starch, 
the  corresponding  quantity  of  copper  is  found. 

The  solution  of  the  metal,  if  it  contain  nitric  acid,  is  evaporated 
with  sulphuric  acid  till  the  former  is  expelled,  or  the  nitric  acid  is 
neutralized  with  sodic  carbonate,  and  acetic  acid  added ;  the  sulphate 
solution  must  be  neutral,  or  only  faintly  acid  ;  excess  of  acetic 
acid  is  of  no  consequence,  but  iron  or  arsenic  acid  must  be  absent, 
as  they  sensibly  affect  the  amount  of  iodine  set  free. 

It  is  always  preferable  to  get  rid  of  all  free  mineral  acids  and 
work  only  with  free  acetic  acid. 

Westmorland  (J".  S.  C.  I.  v.  51),  who  has  had  very  large 
•experience  in  examining  a  variety  of  copper  products,  strongly 
recommends  this  process  for  the  estimation  of  copper  in  its  various 
•ores.  The  metal  may  very  conveniently  be  separated  from  a  hot 
sulphuric  acid  solution  by  sodic  thiosulphate :  this  gives  a  flocculent 
precipitate  of  subsulphide  mixed  with  sulphur,  which  filters  readily, 
and  can  be  washed  with  hot  water.  Arsenic  and  antimony,  if 
present,  are  also  precipitated;  tin,  zinc,  iron,  nickel,  cobalt,  and 
manganese  are  not  precipitated.  On  igniting  the  precipitate  most 
of  the  arsenic  and  the  excess  of  sulphur  is  expelled,  an  impure 
subsulphide  of  copper  being  left.  Sulphuretted  hydrogen  may  of 
course  be  used  instead  of  the  thiosulphate,  but  its  use  is  objection- 

M 


162  VOLUMETRIC   ANALYSIS.  §    54. 

able  to  many  operators.  Kick  copper  ores,  matts,  or  precipitates, 
are  dissolved  in  appropriate  solvents,  and  a  quantity  representing 
about  0'5  gm.  Cu  taken  for  analysis.  The  metal  is  separated 
either  with  thiosulphate  or  H2S,  the  sulphide  dissolved  in 
nitric  acid,  evaporated  with  sulphuric  acid  to  separate  lead, 
diluted,  filtered,  sodic  carbonate  added  in  excess,  and  then 
acetic  acid  to  acid  reaction.  Cupreous  pyrites,  burnt  ores,  etc.,  are 
taken  in  larger  quantity,  according  to  their  contents  of  copper,  and 
treated  in  the  same  way  ;  or  they  may  be  calcined,  dissolved  in  HC1, 
the  ferric  salt  reduced  by  boiling  with  sodic  sulphide,  and  H2S 
passed  through  the  cold  solution :  the  precipitated  sulphides  are 
then  treated  as  before. 

Standardizing  the  Thiosulphate  Solution. — This  is  best  done  on 
pure  electrotype  copper,  dissolved  first  in  nitric  acid,  boiling  to 
expel  nitrous  fumes,  diluting,  neutralizing  with  sodic  carbonate  till 
a  precipitate  occurs,  then  adding  acetic  acid  till  clear.  The  liquid 
is  then  made  up  to  a  definite  volume,  and  a  quantity  equal  to  about 
0*5  gm.  Cu  taken  in  a  flask  or  beaker,  a  few  crystals  of  potassic 
iodide  added,  and  when  dissolved  the  thiosulphate  is  run  in  from 
a  burette  until  the  free  iodine  is  nearly  removed,  add  then  some 
starch,  and  finish  the  titration  in  the  usual  way.  The  thiosulphate 
will  of  course  need  to  be  checked  occasionally,  as  it  is  not 
permanent. 

If  strictly  -^  thiosulphate  is  used,  each  c.c.  =0*0063  gm.  Cu. 

4.    Estimation   by   Potassic    Cyanide    (Parkes   and   C.    Mohr). 

This  well-known  and  much-used  process  for  estimating  copper 
depends  upon  the  decoloration  of  an  ammoniacal  solution  of  copper 
by  potassic  cyanide.  The  reaction  (which  is  not  absolutely  uniform 
with  variable  quantities  of  ammonia)  is  such  that  a  double  cyanide 
of  copper  and  ammonia  is  formed ;  cyanogen  is  also  liberated,  which 
reacts  on  the  free  ammonia,  producing  urea,  oxalate  of  urea, 
ammonic  cyanide  and  formate  (Liebig).  Owing  to  the  influence 
exercised  by  variable  quantities  of  ammonia,  or  its  neutral  salts, 
upon  the  decoloration  of  a  copper  solution  by  the  cyanide,  it  has 
been  suggested  by  Beringer  to  substitute  some  other  alkali  for 
neutralizing  the  free  acid  in  the  copper  solution  other  than 
ammonia.  The  suggestion  has  been  adopted  by  Da  vies  (C.  N. 
Iviii.  131)  and  by  Fessenden  (C.  N.  Ixi.  131),  who  both 
recommend  sodic  carbonate.  My  own  experiments  completely 
confirm  their  statement  that  none  of  the  irregularity  common  to 
variable  quantities  of  ammonia  or  its  salts  occurs  with  soda  or 
potash.  Suppose  for  example  that  copper  has  been  separated  as 
sulphide,  and  brought  into  solution  by  nitric  acid,  the  free  nitro- 
sulphuric  acid  is  neutralized  with  Na2C03,  and  an  excess  of  it 
added  to  redisr.olve  the  precipitate.  The  cyanide  solution  is  then 
cautiously  ran  into  the  light  blue  solution  until  the  colour  is  just 


§  54.  COPPEK.  163 

discharged.  My  own  experience  is,  that  it  is  impossible  to 
redissolve  the  whole  of  the  precipitate  without  using  a  very  large 
excess  of  soda ;  but  there  is  no  need  to  add  such  an  excess,  as 
the  precipitate  easily  dissolves  when  the  cyanide  is  added. 
I  have  used  a  modification  of  this  method,  which  gives  excellent 
results,  viz.,  to  neutralize  the  acid  copper  solution  either  with 
]S"a2C03  or  ISraHO,  add  a  trifling  excess,  and  then  1  c.c.  of 
ammonia  0'960  sp.  gr. ;  a  deep  blue  clear  solution  is  at  once  given, 
Avhich  permits  of  very  sharp  end-reaction  with  the  cyanide. 

J.  J.  and  C.  Beringer  (C.  N.  xlix.  iii.)  have  already  adopted 
the  method  of  neutralizing  the  acid  copper  solution  with  soda, 
then  adding  ammonia,  but  the  proportion  they  recommend  is  larger 
than  necessary. 

In  standardizing  the  cyanide,  it  is  advisable  to  arrange  so  that 
copper  is  precipitated  with  soda  exactly  as  in  the  titration  of 
a  copper  ore;  that  is  to  say,  free  nitric  or  nitro-sulphuric  acid 
should  be  added,  then  neutralized  with  slight  excess  of  soda, 
cleared  with  1  c.c.  of  ammonia,  then  titrated  with  cyanide.  Large 
quantities  of  nitrate  or  sulphate  of  soda  or  potash,  however,  make 
very  little  difference  in  the  quantity  of  cyanide  used. 

It  has  generally  been  thought  that  where  copper  and  iron  occur  together, 
it  is  necessary  to  separate  the  latter  before  using  the  cyanide.  F.  Field, 
however,  has  stated  that  this  is  not  necessary  (C.  N.  i.  25) ;  and  I  can  fully 
endorse  his  statement  that  the  presence  of  the  suspended  ferric  oxide  is  no 
hindrance  to  the  estimation  of  the  copper ;  in  fact,  it  is  rather  an  advantage, 
as  it  acts  as  an  indicator  to  the  end  of  the  process. 

"While  the  copper  is  in  excess,  the  oxide  possesses  a  purplish-brown  colour, 
but  as  this  excess  lessens,  the  colour  becomes  gradually  lighter,  until  it  is 
orange  brown.  If  it  be  now  allowed  to  settle,  which  it  does  very  rapidly,  the 
clear  liquid  above  will  be  found  nearly  colourless.  A  little  practice  is  of 
course  necessary  to  enable  the  operator  to  hit  the  exact  point. 

It  is  impossible  to  separate  the  ferric  oxide  by  filtration  without 
leaving  some  copper  in  it,  and  no  amount  of  washing  will  remove 
it.  For  example,  10  c.c.  of  a  copper  solution  with  10  c.c.  of  ferric 
solution  were  directly  titrated  with  cyanide  after  treatment  with 
^aHO  in  slight  excess  and  1  c.c.  of  ammonia.  The  cyanide 
required  was  12  c.c.  Another  10  c.c.  of  the  same  copper  and  iron 
solutions  were  then  precipitated  with  soda  and  ammonia  in  same 
proportions.  This  gave  a  complete  solution  of  the  copper  with  the 
ferric  oxide  suspended  in  it.  The  solution  was  filtered,  and  the 
ferric  oxide  well  washed  with  hot  water,  then  the  filtrate  cooled  and 
titrated  with  cyanide,  9*5  c.c.  only  being  required.  On  treating  the 
ferric  oxide  on  the  filter  with  nitric  acid,  neutralizing  with  NaHO 
and  NH3  in  proper  proportions  exactly,  2*5  c.c.  of  cyanide  were 
required,  showing  that  the  ferric  oxide  had  retained  20  per  cent, 
of  the  copper. 

I  strongly  recommend  that  operators  who  have  to  deal  with 
copper  determinations  upon  samples  containing  much  iron,  should 

M  2 


164  VOLUMETBIC  ANALYSIS.  §    54. 

practise  the  use  of  the  cyanide  method  in  the  presence  of  the  iron, 
and  accustom  their  eyes  to  the  exact  colour  which  the  ferric  oxide 
takes  when  the  titration  is  finished,  always,  however,  with  this 
proviso,  that  the  cyanide  solution  is  standardized  upon  a  known 
weight  of  copper  in  the  presence  of  a  moderate  amount  of  iron. 

The  solution  of  potassic  cyanide  should  be  titrated  afresh  at 
intervals  of  a  few  days.  Further  details  of  this  process  are  given 
in  §  54.8. 

5.      Estimation    as    Sulphide    (Pelouze). 

It  is  first  necessary  to  have  a  solution  of  pure  copper  of  known 
strength,  which  is  best  made  by  dissolving  39'523  gin.  of  pure 
cupric  sulphate  in  1  liter  of  water ;  each  c.c.  will  contain 
0-01  gm.  Cu. 

Precipitation  in  Alkaline  Solution. — This  process  is  based  on  the 
fact  that  if  an  ammoniacal  solution  of  copper  is  heated  to  from  40° 
to  80°  C.,  and  a  solution  of  sodic  sulphide  added,  the  whole  of 
the  copper  is  precipitated  as  oxysulphide,  leaving  the  liquid 
colourless.  The  loss  of  colour  indicates,  therefore,  the  end  of  the 
process,  and  this  is  its  weak  point.  Special  practice,  however,  will 
enable  the  operator  to  hit  the  exact  point  closely. 

Example :  A  measured  quantity  (say  50  c.c.)  of  standard  solution  of  copper 
is  freely  supersaturated  with  caustic  ammonia,  and  heated  till  it  begins  to 
boil.  The  temperature  will  not  be  higher  than  80°  C,  in  consequence  of  the 
presence  of  the  ammonia  ;  it  is  always  well,  however,  to  use  a  thermometer. 
The  sodic  sulphide  is  delivered  cautiously  from  a  Mohr's  burette,  until  the 
last  traces  of  blue  colour  have  disappeared  from  the  clear  liquid  above  the 
precipitate.  The  experiment  is  repeated,  and  if  the  same  result  is  obtained, 
the  number  of  c.c.  or  dm.  required  to  precipitate  the  amount  of  copper 
contained  in  50  c.c.  or  dm.=0'5  gm.  or  5  grn.  respectively,  is  marked  upon 
the  alkaline  sulphide  bottle.  As  the  strength  of  the  solution  gradually 
deteriorates,  it  must  be  titrated  afresh  every  day  or  two.  Special  regard 
must  be  had  to  the  temperature  of  the  precipitation,  otherwise  the  accuracy 
of  the  process  is  seriously  interfered  with. 

Casamaj  or  (C.  N.  xlv.  167)  uses  instead  of  ammonia  the  alkaline 
tartrate  solution  same  as  for  Fehling,  adding  a  slight  excess  so  as 
to  make  a  clear  blue  solution.  The  addition  of  the  sulphide  gives 
an  intense  black  brown  precipitate,  which  is  stirred  vigorously  till 
clear.  The  copper  sulphide  agglomerates  into  curds,  and  the 
reagent  is  added  until  no  further  action  occurs  with  a  drop  of 
the  sodic  sulphide.  This  modification  can  also  be  used  for  lead. 
PbSO4  is  easily  soluble  in  the  tartrate  solution,  and  can  be  estimated 
by  the  sodic  sulphide  in  the  same  way  as  copper. 

The  colour  of  the  solution  is  not  regarded,  but  the  clotty 
precipitate  of  sulphide,  which  is  easily  cleared  by  vigorous  stirring. 
Very  good  results  may  be  gained  by  this  modification. 

Copper  can  also  be  first  separated  by  glucose,  or  as  sulphocyanate 
(Rivot),  then  dissolved  in  HNO3,  and  treated  with  the  tartrate. 


§  54.  COPPER.  165 

Precipitation  in  Acid  Solution. — The  copper  solution  is  placed 
in  a  tall  stoppered  flask  of  tolerable  size  (400  or  500  c.c.),  freely 
acidified  with  hydrochloric  acid,  then  diluted  with  about  200  c.c. 
of  hot  water. 

The  alkaline  sulphide  is  then  delivered  in  from  a  burette^ 
the  stopper  replaced,  and  the  mixture  well  shaken  •  the  precipitate 
of  copper  sulphide  settles  readily,  leaving  the  supernatant  liquid 
clear ;  fresh  sulphide  solution  is  then  at  intervals  added  until  no 
more  precipitate  occurs.  The  calculation  is  the  same  as  in  the  case 
of  alkaline  precipitation,  but  the  copper  is  precipitated  as  pure 
sulphide  instead  of  oxysulphide. 

6.      Estimation    by    Stannous    Chloride    (Weil). 

This  process  is  based  on  the  fact,  that  a  solution  of  a  cupric  salt 
in  large  excess  of  hydrochloric  acid  at  a  boiling  heat  shows,  even 
when  the  smallest  trace  is  present,  a  greenish-yellow  colour.  If  to 
such  a  solution  stannous  chloride  is  added  in  minute  excess,  a 
colourless  cuprous  chloride  is  produced,  and  the  loss  of  colour 
indicates  the  end  of  the  process. 

2CuCl2  +  SnCl2  -  Cu2Cl2  +  SnCl4. 

The  change  is  easily  distinguishable  to  the  eye,  but  should  any 
doubt  exist  as  to  whether  stannous  chloride  is  in  excess,  a  small 
portion  of  the  solution  may  be  tested  with  mercuric  chloride.  Any 
precipitate  of  calomel  indicates  the  presence  of  stannous  chloride. 

The  tin  solution  is  prepared  as  described  in  §  33.2. 

A  standard  copper  solution  is  made  by  dissolving  pure  cupric 
sulphate  in  distilled  water,  in  the  proportion  of  39 '523  gm.  per 
liter  =10  gm.  of  Cu. 

Process  for  Copper  alone. — 10  c.c.  of  the  copper  solution =0'1  gm.  of 
Cu  are  put  into  a  white-glass  flask,  25  c.c.  of  pure  strong  hydrochloric  acid 
added,  placed  on  a  sand-bath  and  brought  to  boiling  heat ;  the  tin  solution  is 
then  quickly  delivered  in  from  a  burette  until  the  colour  is  nearly  destroyed, 
finally  a  drop  at  a  time  till  the  liquid  is  as  colourless  as  distilled  water.  No 
oxidation  will  take  place  during  the  boiling,  owing  to  the  flask  being  filled 
with  acid  vapours. 

A  sample  of  copper  ore  is  prepared  in  the  usual  way  by  treatment  with 
nitric  acid,  which,  is  afterwards  removed  by  evaporating  with  sulphuric  acid. 
Silica,  lead,  tin,  silver,  or  arsenic,  are  of  no  consequence,  as  when  the  solution 
is  diluted  with  water  to  a  definite  volume,  the  precipitates  of  these  substances 
settle  to  the  bottom  of  the  measuring  flask,  and  the  clear  liquid  may 
be  taken  out  for  titration.  In  case  antimonic  acid  is  present  it  will  be 
reduced  with  the  copper,  but  on  exposing  the  liquid  for  a  night  in  an  open 
basin,  the  copper  will  be  completely  re-oxidized  but  not  the  antimony; 
a  second  titration  will  then  show  the  amount  of  copper. 

Process  for  Ores  containing-  Copper  and  Iron. — In  the  case  of  copper 
ores  where  iron  is  also  present,  the  quantity  of  tin  solution  required  will  of 
course  represent  both  the  iron  and  the  copper.  In  this  case  a  second  titration 
of  the  original  solution  is  made  with  zinc  and  permanganate,  and  the  quantitv 


166  VOLUMETRIC   ANALYSIS.  §    54. 

so  found  is  deducted  from  the  total  quantity ;  the  amount  of  tin  solution 
corresponding  to  copper  is  thus  found. 

Example :  A  solution  was  prepared  from  10  gm.  of  ore  and  diluted  to 
250  c.c. :  10  c.c.  required  2675  c.c.  of  tin  solution  whose  strength  was 
16'2  c.c.  for  O'l  gm.  of  Cu. 

10  c.c.  of  ore  solution  were  diluted,  warmed,  zinc  and  platinum  added  till 
reduction  was  complete,  and  the  solution  titrated  with  permanganate  whose 
quantity  =  0-0809  gm.  of  Fe. 

The  relative  strength  of  the  tin  solution  to  iron  is  18'34  c.c.  =  0'l  gm. 
of  Fe:  thus— 

63  :  56         =0'1     :     O'OSSS. 

therefore  O'l  gm.  of  Cu  =  0'OSS8  gm.  of  Fe=16'2  c.c.  of  SnCP 
whence    0'0888     :     0'1  =  16'2     :     18'34 
thus         0*0809  Fe  (found  above)  =  14*837  c.c.  of  SnCl2 
O'l     :     0-0809=18-34     :     14'837  hence 

Iron  and  copper  =    26'750  c.c.  SnCl2 

Subtract  for  iron          =    14'837 

Leaving  for  copper  11'913 

10  c.c.  of  ore  solution  therefore  contained  16'2  :  O'l  :  :  ir913  =  0'0735  gm. 
of  Cu,  and  as  10  gm.  of  ore  =  250  c.c.  contained  T837  gm.  of  Cu=  18"37  per 
cent.    Analysis  by  weight  as  a  control  gave  18'34  per  cent.  Cu. 
Fe  volumetrically  20'25  per  cent.,  by  weight  20'10  per  cent. 

The  method  is  specially  adapted  to  the  analysis  of  fahl-ores. 

Process  for  Ores  containing  Nickel  or  Cobalt. — The  ore  is  dissolved 
in  nitric  or  nitro-hydrochloric  acid,  then  nearly  neutralized  with  sodic 
carbonate,  diluted  with  cold  water,  and  freshly  precipitated  baric  carbonate 
and  some  ammonic  chloride  added;  the  whole  is  well  mixed  together, 
producing  a  precipitate  containing  all  the  copper  and  iron,  while  the  nickel 
or  cobalt  remains  in  solution ;  the  precipitate  is  first  washed  by  decantation, 
collected  on  a  filter,  well  washed,  then  dissolved  in  hydrochloric  acid,  and 
titrated  with  stannous  chloride  as  before  described. 

Method  for  Copper,  Iron,  and  Antimony. — The  necessary  solutions 
are : — (1)  Standard  copper.  19'667  gm.  of  copper  sulphate  are  dissolved 
in  water  to  500  c.c.  (2)  A  similar  solution  containing  7"867  gm.  of  copper 
sulphate.  (3)  Standard  tin  solution.  4'5  to  5  gm.  of  stannous  chloride, 
and  230  gm.  of  HC1,  are  made  up  to  500  c.c.  with  water.  This  solution  is 
standardized  with  No.  1,  10  c.c.  of  which  solution  should  be  mixed  with 
25  c.c.  hydrochloric  acid,  boiled,  and  the  tin  solution  to  be  standardized  run 
in  until  the  green  colour  disappears. 

Estimation  of  Copper. — 5  gm.  of  substance  are  dissolved  in  HC1  or 
H2SO4,  and  made  up  to  250  c.c.  10  c.c.  of  this  solution  are  taken,  25  c.c. 
HC1  added,  and  then  titrated  as  above. 

Estimation  of  Iron. — When  there  are  2|  vols.  of  free  HC1  to  1  vol.  of 
the  ferric  solution  no  indicator  is  necessary,  and  the  standard  tin  solution  is 
run  in  until  the  iron  solution  is  colourless ;  in  this  way  the  quantity  of  iron 
is  obtained  in  terms  of  copper.  Of  solutions  containing  2  gm.  of  the  sample 
in  250  c.c.,  10  c.c.  are  evaporated  in  a  porcelain  capsule,  with  10  c.c.  of  the 
copper  solution  (No.  2) ;  to  the  concentrated  mixed  solution  large  excess 
(about  75  c.c.)  of  HC1  is  added,  and  this  is  titrated  with  the  tin  solution  as 
before.  Of  course  the  tin  required  for  the  copper  used  must  be  deducted. 
The  copper  is  used  as  an  indicator,  and  is  not  required  with  substances  con- 
taining more  than  2  per  cent,  of  iron. 


§  54  COPPER.  167 

Estimation  of  Iron  and  Copper.— 5  gm.  of  ore  in  250  c.c.  Titrate  as 
before  directed.  In  another  10  c.c.  of  solution,  precipitate  the  copper  with 
.zinc,  filter,  reconvert  the  ferrous  into  ferric  salt  by  means  of  permanganate, 
and  titrate  the  iron  again. 

Estimation  of  Antimony. — In  making  up  the  250  c.c.  in  this  case,  it  is 
necessary  to  use  aqueous  solution  of  tartaric  acid  to  prevent  precipitation  of 
antimony.  The  solution  of  antimonic  chloride  is  mixed  with  No.  1  copper 
solution  and  a  large  excess  of  HC1,  then  titrated ;  the  c.c.  of  standard  tin 
solution  used  indicates  the  sum  of  the  Cu  and  Sb.  If  the  mixed  solution  of 
cuprous  and  antimonious  chloride  is  allowed  to  remain  some  hours  the  Cu 
becomes  re-oxidized,  but  the  Sb  does  not,  therefore  a  second  titration  gives 
the  quantity  of  Cu  only ;  this  is  scarcely  required  when  the  strength  and 
quantity  of  copper  solution  added  is  known. 

Antimony,  Copper,  and  Iron,  when  together  in  same  sample,  are  thus 
t  determined.  5  gm.  substance  is  dissolved  in  nitric  acid,  evaporated  down, 
and  filtered.  The  filtrate  contains  iron  and  copper,  which  are  determined  as 
above  directed.  The  precipitate  contains  all  the  antimony ;  it  is  dissolved  in 
HC1,  treated  with  permanganate,  and  the  antimonic  chloride  determined  as 
directed. 

This  process  depends  on  the  reducing  action  of  stannous  chloride.  It  is 
therefore  necessary  to  get  rid  of  extraneous  oxidizing  influences,  such  as 
free  chlorine,  nitric  acid,  or  excess  of  permanganate,  etc.,  before  titration ; 
this  is  effected  by  evaporating  to  dryness,  taking  up  with  hydrochloric  acid, 
and  repeating,  until  the  solution  or  vapour  evolved  on  boiling  ceases  to  turn 
iodized  starch-paper  blue. 

7.      Volhard's    method. 

The  necessary  standard  solutions  are  described  in  §  39.  Each  c.c. 
of  ~j  thiocyanate  represents  0'0063  gm.  Cu. 

The  Analysis :  The  copper  in  sulphuric  or  nitric  acid  solution  is  evaporated 
to  remove  excess  of  acid,  or  if  the  acid  is  small  in  quantity  neutralized  with 
sodic  carbonate,  washed  into  a  300  c.c.  flask,  and  enough  aqueous  solution  of 
SO2  added  to  dissolve  the  traces  of  basic  carbonate  and  leave  a  distinct  smell 
of  SO2.  Heat  to  boiling,  and  run  in  from  a  burette  the  thiocyanate  until  the 
addition  produces  no  change  of  colour,  add  3  or  4  c.c.,  and  note  the  entire 
quantity,  allow  to  cool,  fill  to  mark,  and  shake  well.  100  c.c.  are  then  filtered 
through  a  dry  filter,  10  c.c.  of  ferric  indicator  with  some  nitric  acid  added, 
then  titrated  with  •£$•  silver  till  colourless ;  then  again  thiocyanate  till  the 
reddish  colour  occurs.  The  volume  of  silver  solution,  less  the  final  correction 
with  thiocyanate,  deducted  from  the  original  thiocyanate,  will  give  the 
volume  of  the  latter  required  to  precipitate  the  copper. 

The  process  is  not  accurate  in  presence  of  Fe,  Ag,  Hg,  Cl,  I  or  Br. 


8.    Technical    Examination    of    Copper    Ores    (Steinbeck's 
Process). 

In  1867  the  Directors  of  the  Mansfield  Copper  Mines  offered  a 
premium  for  the  best  method  of  examining  these  ores,  the  chief 
conditions  being  tolerable  accuracy,  simplicity  of  working,  and  the 
possibility  of  one  operator  making  at  least  eighteen  assays  in  the  day. 

The  fortunate  competitor  was  Dr.  Steinbeck,  whose  process 
satisfied  completely  the  requirements.  The  whole  report  is  con- 


168 


VOLUMETRIC  ANALYSIS. 


§    54. 


tained  in  Z.  a.  C.  viii.  1,  and  is  also  translated  in  C.  N.  xix.  181. 
The  following  is  a  condensed  resume  of  the  process,  the  final 
titration  of  the  copper  being  accomplished  by  potassic  cyanide  as  in 
§  54.4.  A  very  convenient  arrangement  for  filling  the  burette 
with  standard  solution  where  a  series  of  analyses  has  to  be  made, 
and  the  burette  continually  emptied,  is  shown  in  fig.  33  :  it  may 
be  refilled  by  simply  blowing  upon  the  surface  of  the  liquid. 


Fig.  33. 

(a)  The  extraction  of  the  Copper  from  the  Ore. — 5  gm.  of  pulverized 
ore  are  put  into  a  flask  with  from  40  to  50  c.c.  of  crude  hydrochloric  acid 
(specific  gravity  1*16),  whereby  all  carbonates  are  converted  into  chlorides, 
while  carbonic  acid  is  expelled.  After  a  while  there  is  added  to  the  fluid  in 
the  flask  6  c.c.  of  a  special  nitric  acid,  prepared  by  mixing  equal  bulks  of 
water  and  pure  nitric  acid  of  1'2  sp.  gr.  As  regards  certain  ores,  however, 
specially  met  with  in  the  district  of  Mansfield,  some,  having  a  very  high 
percentage  of  sulphur  and  bitumen,  have  to  be  roasted  previous  to  being- 
subjected  to  this  process ;  and  others,  again,  require  only  1  c.c.  of  nitric  acid 
instead  of  6.  The  flask  containing  the  assay  is  digested  on  a  sand-bath  for 


§54.  COPPEK.  169 

half  an  hour,  and  the  contents  boiled  for  about  fifteen  minutes ;  after  which 
the  whole  of  the  copper  occurring  in  the  ore,  and  all  other  metals,  are  in 
solution  as  chlorides.  The  blackish  residue,  consisting  of  sand  and  schist, 
has  been  proved  by  numerous  experiments  to  be  either  entirely  free  from 
copper,  or  to  contain  at  the  most  only  O'Ol  to  0'03  per  cent. 

(b)  Separation  of  the  Copper. — The  solution  of   metallic  and  earthy 
chlorides,  and  some  free  HC1,  obtained  as  just  described,  is  separated  by 
filtration  from  the  insoluble  residue,  and  the  fluid  run  into  a  covered  beaker 
of  about  400  c.c.  capacity.     In  this  beaker  a  rod  of  metallic  zinc,  weighing 
about  50   gm.,  has  been  previously  placed,  fastened  to  a  piece  of  stout 
platinum  foil.     The  zinc  to  be  used  for  this  purpose  should  be  as  much  as 
possible  free  from  lead,  and  at  any  rate  should  not  contain  more  than  from 
O'l  to  03  per  cent,  of  the  latter  metal.     The  precipitation  of  the  copper  in 
the  metallic  state  sets  in  already  during  the   filtration  of   the  warm  and 
concentrated  fluid,  and  is,  owing  especially  also  to  the  entire  absence  of 
nitric  acid,  completely  finished  in  from  half  to  three  quarters  of  an  hour  after 
the  beginning  of  the  filtration.    If  the  fluid  be  tested  with  SH2,  no  trace 
of  copper  can  or  should  be  detected ;  the  spongy  metal  partly  covers  the 
platinum  foil,  partly  floats  about  in  the  liquid,  and  in  case  either  the  ore 
itself  or  the  zinc  applied  in  the  experiment  contained  lead,  small  quantities 
of  that  metal  will  accompany  the  precipitated  copper.    After  the  excess  of 
zinc  (for  an  excess  must  always  be  employed)  has  been  removed,  the  metal  is 
repeatedly  and  carefully  washed  by  decantation  with  fresh  water,  and  care 
taken  to  collect  together  every  particle  of  the  spongy  mass. 

(c)  Estimation  of  the  precipitated  Copper. — To  the  spongy  metallic 
mass  in  the  beaker  glass,  wherein  the  platinum  foil  is  left,  since  some  of  the 
metal  adheres  to  it,  8  c.c.  of  the  special  nitric  acid  are  added,  and  the  copper 
dissolved  by  the  aid  of  moderate  heat  in  the  form  of  cupric  nitrate,  which, 
in  the  event  of  any  small  quantity  of  lead  being  present,  will  of  course  be 
contaminated  with  lead. 

When  copper  ores  are  dealt  with  containing  above  6  per  cent,  of  copper, 
which  may  be  approximately  estimated  from  the  bulk  of  the  spongy  mass  of 
precipitated  metal,  16  c.c.  of  nitric  acid,  instead  of  8,  are  applied  for 
dissolving  the  metal.  The  solution  thus  obtained  is  left  to  cool,  and  next 
mixed,  immediately  before  titration  with  potassic  cyanide,  with  10  c.c.  of 
special  solution  of  liquid  ammonia,  prepared  by  diluting  1  volume  of  liquid 
ammonia  (sp.  gr.  0'93)  with  2  volumes  of  distilled  water. 

The  titration  with  cyanide  is  conducted  as  described  in  §  54.4. 

In  the  case  of  such  ores  as  yield  over  6  per  cent,  of  copper,  and  when  a 
double  quantity  of  nitric  acid  has  consequently  been  used,  the  solution  is 
diluted  with  water,  and  made  to  occupy  a  bulk  of  100  c.c. ;  this  bulk  is  then 
exactly  divided  into  two  portions  of  50  c.c.  each,  and  each  of  these  separately 
mixed  with  10  c.c.  of  ammonia,  and  the  copper  therein  volumetrically 
determined.  The  deep  blue  coloured  solution  only  contains,  in  addition  to 
the  copper  compound,  ammonic  nitrate ;  any  lead  which  might  have  been 
dissolved  having  been  precipitated  as  hydrated  oxide,  which  does  not  interfere 
with  the  titration  with  cyanide.  The  solution  of  the  last-named  salt  is  so 
arranged,  that  1  c.c.  thereof  exactly  indicates  0'005  gm.  of  copper.  Since, 
for  every  assay,  5  gm.  of  ore  have  been  taken,  1  c.c.  of  the  titration  fluid  is 
equal  to  O'l  per  cent,  of  copper,  it  hence  follows  that,  by  multiplying  the 
number  of  c.c.  of  cyanide  solution  used  to  make  the  blue  colour  of  the 
copper  solution  disappear  by  O'l,  the  percentage  of  copper  contained  in  the 
ore  is  immediately  ascertained. 

Steinbeck  tested  this  method  specially,  in  order  to  see  what 
influence  is  exercised  thereupon  by  (1)  ammonic  nitrate,  (2)  caustic 


170  VOLUMETRIC   ANALYSIS.  §    54 

ammonia,  (3)  lead.  The  copper  used  for  the  experiments  for  this 
purpose  was  pure  metal,  obtained  by  galvanic  action,  and  was 
ignited  to  destroy  any  organic  matter  which  might  accidentally 
adhere  to  it,  and  next  cleaned  by  placing  it  in  dilute  nitric  acid. 
5  gm.  of  this  metal  were  placed  in  a  liter  flask,  and  dissolved  in 
266 '6  c.c.  of  special  nitric  acid,  the  flask  gently  heated,  and,  after 
cooling,  the  contents  diluted  with  water,  and  thus  brought  to  a 
bulk  of  1000  c.c.  30  c.c.  of  this  solution  were  always  applied  to 
titrate  one  and  the  same  solution  of  cyanide  under  all  circumstances. 
When  5  gm.  of  ore,  containing  on  an  average  3  per  cent,  of  copper, 
are  taken  for  assay,  that  quantity  of  copper  is  exactly  equal  to 
0-150  gm.  of  the  chemically  pure  copper.  The  quantity  of  nitric 
acid  taken  to  dissolve  5  gm.  of  pure  copper  (266 '6  c.c.)  was 
purposely  taken,  so  as  to  correspond  with  the  quantity  of  8  c.c.  of 
special  nitric  acid  which  is  applied  in  the  assay  of  the  copper 
obtained  from  the  ore,  and  this  quantity  of  acid  is  exactly  met 
with  in  30  c.c.  of  the  solution  of  pure  copper. 

The  influence  of  double  quantities  of  ammonic  nitrate  and  free 
caustic  ammonia  (the  quantity  of  copper  remaining  the  same)  is 
shown  as  follows  : — 

(a)  30  c.c.  of  the  normal  solution  of  copper,  containing  exactly  O'ISO  gm. 
of  copper,  were  rendered  alkaline  with  10  c.c.  of  special  ammonia,  and  were 
found  to  require,  for  entire  decoloration,  29'8  c.c.  of  cyanide.  A  second 
experiment,  again  "with  30  c.c.  of  copper  solution,  and  otherwise  under 
identically  the  same  conditions,  required  29'9  c.c.  of  cyanide.  The  average 
is  29'85  c.c. 

(5)  "When  to  30  c.c.  of  the  copper  solution,  first  8  c.c.  of  special  nitric 
acid  are  added,  and  then  20  c.c.  of  special  ammonia  instead  of  only  8,  whereby 
the  quantity  of  free  ammonia  and  of  ammonic  nitrate  is  double  what  it  was 
in  the  case  of  a,  there  is  required  of  the  same  cyanide  30'3  c.c.  to  produce 
decoloration.  A  repetition  of  the  experiment,  exactly  under  the  same 
conditions,  gave  30'4  c.c.  of  the  cyanide ;  the  average  is,  therefore,  30'35  c.c. 
The  difference  amounts  to  only  0'05  per  cent,  of  copper,  which  may  be 
allowed  for  in  the  final  calculation. 

When,  however,  larger  quantities  of  ammoniacal  salts  are  present 
in  the  fluid  to  be  assayed  for  copper,  by  means  of  cyanide,  and 
especially  when  ammonic  carbonate,  sulphate,  and,  worse  still, 
chloride  are  simultaneously  present,  these  salts  exert  a  very  dis- 
turbing influence.*  The  presence  of  lead  in  the  copper  solution 
to  be  assayed  has  the  effect  of  producing,  on  the  addition  of  10  c.c. 
of  normal  ammonia,  a  milkiness  with  the  blue  tint ;  but  this  does 
not  at  all  interfere  with  the  estimation  of  the  copper  by  means 
of  the  cyanide,  provided  the  lead  be  not  in  great  excess ;  and  a 
slight  milkiness  of  the  solution  even  promotes  the  visibility  of  the 
approaching  end  of  the  operation. 

*  I  have  retained  this  technical  process  in  its  original  form,  notwithstanding  the  use 
of  ammonia,  because  it  is  systematic,  and  the  results  obtained  by  it  are  all  comparable 
among  themselves.  Of  course  soda  or  potash  may  be  used  in  place  of  ammonia,  if  the 
cyanide  is  standardized  with  tbem. 


§  54.  COPPEK.  171 

Steinbeck  purposely  made  some  experiments  to  test  this  point, 
and  his  results  show  that  a  moderate  quantity  of  lead  has  no 
influence. 

Experiments  were  also  carefully  made  to  ascertain  the  influence 
of  zinc,  the  result  of  which  showed  that  up  to  5  per  cent,  of  the 
copper  present,  the  zinc  had  no  disturbing  action;  but  a  considerable 
variation  occurred  as  the  percentage  increased  above  that  proportion. 
Care  must  therefore  always  be  taken  in  washing  the  spongy  copper 
precipitated  from  the  ore  solution  by  means  of  zinc. 

The  titratioii  must  always  take  place  at  ordinary  temperatures, 
since  heating  the  ammoniacal  solution  while  under  titration  to  40° 
or  45°  C.  considerably  reduces  the  quantity  of  cyanide  required. 

9.     Estimation   of    Copper   by   Colour   Titration. 

This  method  can  be  adopted  with  very  accurate  results,  as  in  the 
case  of  iron,  and  is  available  for  slags,  poor  cupreous  pyrites, 
waters,  etc.  (see  Carnelly,  C.  N.  xxxii.  308). 

The  reagent  used  is  the  same  as  in  the  case  of  iron,  viz.,  potassic 
ferrocyanide,  which  gives  a  purple-brown  colour  with  very  dilute 
solutions  of  copper.  This  reaction,  however,  is  not  so  delicate  as 
it  is  with  iron,  for  1  part  of  the  latter  in  13,000,000  parts  of  water 
can  be  detected  by  means  of  potassic  ferrocyanide ;  while  1  part 
of  copper  in  a  neutral  solution,  containing  ammonic  nitrate,  can 
only  be  detected  in  2,500,000  parts  of  water.  Of  the  coloured 
reactions  which  copper  gives  with  different  reagents,  those  with 
sulphuretted  hydrogen  and  potassic  ferrocyanide  are  by  far  the 
most  delicate,  both  showing  their  respective  colours  in  2,500,000 
parts  of  water. 

Of  the  two  reagents  sulphuretted  hydrogen  is  the  more  delicate ; 
but  potassic  ferrocyanide  has  a  decided  advantage  over  sulphuretted 
hydrogen  in  the  fact  that  lead,  when  not  present  in  too  large 
quantity,  does  not  interfere  with  the  depth  of  colour  obtained, 
whereas  to  sulphuretted  hydrogen  it  is,  as  is  well  known,  very 
sensitive. 

And  though  iron  if  present  would,  without  special  precaution 
being  taken,  prevent  the  determination  of  copper  by  means  of 
ferrocyanide ;  yet,  by  the  method  as  described  below,  the  amounts 
of  these  metals  contained  together  in  a  solution  can  be  estimated 
by  this  reagent. 

Ammonic  nitrate  renders  the  reaction  much  more  delicate ;  other 
salts,  as  ammonic  chloride  and  potassic  nitrate,  have  likewise  the 
same  effect. 

The  method  of  analysis  consists  in  the  comparison  of  the 
purple-brown  colours  produced  by  adding  to  a  solution  of  potassic 
ferrocyanide — first,  a  solution  of  copper  of  known  strength; 
and,  secondly,  the  solution  in  which  the  copper  is  to  be 
determined. 


172  VOLUMETRIC   ANALYSIS.  §    54. 

The  solutions  and  materials  required  are  as  follows  : — 

(1)  Standard  Copper  solution. — Prepared  by  dissolving  0*395gm. 
of  pure  CuSO4,  5H20  in  one  liter  of  water.     1  c.c.  =  O'l  m.gm.  Cu. 

(2)  Solution  of  Ammonic  nitrate. — Made  by  dissolving  100  gni. 
of  the  salt  in  one  liter  of  water. 

(3)  Potassic  ferrocyanide  solution. — 1   :  25. 

(4)  Two  glass  cylinders  holding  rather  more  than  150  c.c.  each, 
the  point  equivalent  to  that  volume  being  marked  on  the  glass. 
They  must  both  be  of  the  same  tint,  and  as  colourless  as  possible. 
Instead  of  these  the  colorimeter  may  be  used. 

A  burette,  graduated  to  y1^  c.c.  for  the  copper  solution ;  a  5  c.c. 
pipette  for  the  ammonic  nitrate ;  and  a  small  tube  to  deliver  the 
ferrocyanide  in  drops. 

The  Analysis :  Five  drops  of  the  potassic  ferrocyanide  are  placed  in  each 
cylinder,  and  then  a  measured  quantity  of  the  neutral  solution  in  which 
the  copper  is  to  be  determined  is  placed  into  one  of  them,  and  both  filled 
up  to  the  mark  with  distilled  water,  5  c.c.  of  the  ammonic  nitrate  solution 
added  to  each,  and  then  the  standard  copper  solution  ran  gradually  into 
the  other  till  the  colours  in  both  cylinders  are  of  the  same  depth,  the 
liquid  being  well  stirred  after  each  addition.  The  number  of  c.c.  used  are 
then  read  off.  Each  c.c.  corresponds  to  O'l  m.gm.  of  copper,  from  which 
the  amount  of  copper  in  the  solution  in  question  can  be  calculated. 

The  solution  in  which  the  copper  is  to  be  estimated  must  be 
neutral ;  for  if  it  contain  free  acid  the  latter  lessens  the  depth  of 
colour,  and  changes  it  from  a  purple-brown  to  an  earthy  brown.  If 
it  should  be  acid,  it  is  rendered  slightly  alkaline  with  ammonia, 
and  the  excess  of  the  latter  got  rid  of  by  boiling.  The  solution 
must  not  be  alkaline,  as  the  brown  coloration  is  soluble  in  ammonia 
and  decomposed  by  potash  or  soda ;  if  it  be  alkaline  from  ammonia, 
this  is  remedied  as  before  by  boiling  it  off;  while  free  potash  or 
soda,  should  they  be  present,  are  neutralized  by  an  acid,  and  the 
latter  by  ammonia. 

Lead,  when  present  in  not  too  large  quantity,  has  little  or  no 
effect  on  the  accuracy  of  the  method.  The  precipitate  obtained  on 
adding  potassic  ferrocyanide  to  a  lead  salt  is  white  ;  and  this,  except 
when  present  in  comparatively  large  quantity  with  respect  to  the 
copper,  does  not  interfere  with  the  comparison  of  the  colours. 

When  copper  is  to  be  estimated  in  a  solution  containing  iron,  the 
following  method  is  adopted  : — 

A  few  drops  of  nitric  acid  are  added  to  the  solution  in  order  to  oxidize  the 
iron,  the  liquid  evaporated  to  a  small  bulk,  and  the  iron  precipitated  by 
ammonia.  Even  when  very  small  quantities  of  iron  are  present,  this  can  bo 
done  easily  and  completely  if  there  be  only  a  very  small  quantity  of  fluid. 
The  precipitate  of  ferric  oxide  is  then  filtered  off,  washed  once,  dissolved  in 
nitric  acid,  and  re-precipitated  by  ammonia,  filtered  and  washed.  The  iron 
precipitate  is  now  free  from  copper,  and  in  it  the  iron  can  be  estimated  by 
dissolving  in  nitric  acid,  making  the  solution  nearly  neutral  with  ammonia, 
and  determining  the  iron  by  the  method  in  §  60.4.  The  filtrate  from  the 
iron  precipitate  is  boiled  till  the  ammonia  is  completely  driven  off,  and  the 
copper  estimated  in  the  solution  so  obtained  as  already  described. 


§    55.  CYANOGEN.  1*73 

"When  the  solution  containing  copper  is  too  dilute  to  give  any 
coloration  directly  with  ferrocyanide,  a  measured  quantity  of  it 
must  be  evaporated  to  a  small  bulk,  and  filtered  if  necessary  ; 
and  if  it  contain  iron,  also  treated  as  already  described. 

In  the  determination  of  copper  and  iron  in  water,  for  which  the 
method  is  specially  applicable,  a  measured  quantity  is  evaporated 
to  dryness  with  a  few  drops  of  nitric  acid,  ignited  to  get  rid  of  any 
organic  matter  that  might  colour  the  liquid,  dissolved  in  a  little 
boiling  water  and  a  drop  or  two  of  nitric  acid;  if  it  is  not  all 
soluble  it  does  not  matter.  Ammonia  is  next  added  to  precipitate 
the  iron,  the  latter  filtered  off,  washed,  re-dissolved  in  nitric  acid, 
and  again  precipitated  by  ammonia,  filtered  off,  and  washed.  The 
iiltrate  is  added  to  the  one  previously  obtained,  the  iron  estimated 
in  the  precipitate,  and  the  copper  in  the  united  filtrates. 

CYANOGEN. 


1  c.c.  ~  silver  solution  =  0*0052  gm. 

Cyanogen. 
-  0-0054  gm. 

Hydrocyanic  acid. 
=  0-01302  gm. 

Potassic  cyanide. 
„       iodine  solution   =  0  '003255  gm. 

Potassic  cyanide. 

1.     By   Standard   Silver   Solution    (Liebig). 

§  55.  THIS  ready  and  accurate  method  of  estimating  cyanogen 
in  prussic  acid,  alkaline  cyanides,  etc.,  was  discovered  by  Lie  big, 
and  is  fully  described  in  Ann.  der  Cliem.  und  Pliarm.  Ixxvii.  102. 
It  is  based  on  the  fact,  that  when  a  solution  of  silver  nitrate  is 
added  to  an  alkaline  solution  containing  cyanogen,  with  constant 
stirring,  no  permanent  precipitate  of  silver  cyanide  occurs  until  all 
the  cyanogen  has  combined  with  the  alkali  and  the  silver,  to  form 
a  soluble  double  salt  (in  the  presence  of  potash,  for  example, 
KCy,  AgCy).  If  the  slightest  excess  of  silver,  over  and  above  the 
quantity  required  to  form  this  combination,  be  added,  a  permanent 
precipitate  of  silver  cyanide  occurs,  the  double  compound  being 
destroyed.  If,  therefore,  the  silver  solution  be  of  known  strength, 
the  quantity  of  cyanogen  present  is  easily  found  ;  1  eq.  of  silver  in 
this  case  being  equal  to  2  eq.  cyanogen. 

So  fast  is  this  double  combination,  that,  when  sodic  chloride  is 
present,  no  permanent  precipitate  of  silver  chloride  occurs,  until  the 
quantity  of  silver  necessary  to  form  the  compound  is  slightly  over- 
stepped. 

Siebold,  however,  has  pointed  out  that  this  process,  in  the  case 


174  VOLUMETRIC   ANALYSIS.  §    55. 

of    free  hydrocyanic  acid,   is  liable  to  serious  errors  unless  the 
following  precautions  are  observed  : — 

(a)  The  solution  of  sodic  or  potassic  hydrate  should  be  placed  in  the 
beaker  first,  and  the  hydrocyanic  acid  added  to  it  from  a  burette  dipping 
into  the  alkali.    If,  instead  of  this,  the  acid  is  placed  in  the  beaker  first,  and 
the  alkaline   hydrate   added   afterwards,  there  may  be  a  slight   loss  by 
evaporation,  which  becomes  appreciable  whenever  there  is  any  delay  in  the 
addition  of  the  alkali. 

(b)  The  mixture  of  hydrocyanic  acid  and  alkali  should  be  largely  diluted 
with  water  before  the  silver  nitrate  is  added.     The  most  suitable  proportion 
of  water  is  from  ten  to  twenty  times  the  volume  of  the  officinal  or  of 
Scheele's  acid.    "With  such  a  degree  of  dilution,  the  final  point  of  the 
reaction  can  be  observed  with  greater  precision. 

(c)  The  amount  of  alkali  used  should  be  as  exactly  as  possible  that 
required  for  the  conversion  of  the  hydrocyanic  acid  into  alkaline  cyanide, 
as  an  insufficiency  or  an  excess  both  affect  the  accuracy  of  the  result.    It  is 
advisable  to  make  first  a  rough  estimation  with  excess  of  soda  as  a  guide, 
then  finish  with  a  solution  as  neutral  as  possible. 

Caution. — In  using  the  pipette  for  measuring  hydrocyanic  acid, 
it  is  advisable  to  insert  a  plug  of  cotton  wool,  slightly  moistened 
with  silver  nitrate,  into  the  upper  end,  so  as  to  avoid  the  danger  of 
inhaling  any  of  the  acid ;  otherwise  it  is  decidedly  preferable  to 
weigh  it. 

Example  with  Potassic  Cyanide :  The  quantity  of  this  substance  necessary 
to  be  taken  for  analysis,  so  that  each  c.c.  or  dm.  shall  be  equal  to  1  per  cent, 
of  the  pure  cyanide,  is  1'30  gm.  or  13'0  grn.  13  grains,  therefore,  of  the 
commercial  article  were  dissolved  in  water,  no  further  alkali  being  necessar}', 
and  54  dm.  ^  silver  required  to  produce  the  permanent  turbidity.  Hie 
sample  therefore  contained  54  per  cent,  of  real  cyanide. 

2.     By   Standard  Mercuric   Chloride    (Hannay). 

This  convenient  method  is  fully  described  by  the  author  (J.  C.  S. 
1878,  245),  and  is  well  adapted  for  the  technical  examination  of 
commercial  cyanides,  etc.,  giving  good  results  in  the  presence  of 
cyanates,  sulphocyanates,  alkaline  salts,  and  compounds  of  ammonia 
and  silver. 

The  standard  solution  of  mercury  is  made  by  dissolving  13 '5 3  7 
gm.  HgCl2  in  water,  and  diluting  to  a  liter.  Each  c.c.  =  0*00651  gm. 
of  potassic  cyanide  or  0'0026  gm.  Cy. 

The  Analysis .-  The  cyanide  is  dissolved  in  water,  and  the  beaker  placed 
upon  black  paper  or  velvet ;  ammonia  is  then  added  in  moderate  quantity,, 
and  the  mercuric  solution  cautiously  added  with  constant  stirring  until  a 
bluish-white  opalescence  is  permanently  produced.  With  pure  substances 
the  reaction  is  very  delicate,  but  not  so  accurate  with  impure  mixtures 
occurring  in  commerce. 

3.     By  Iodine    (Fordos   and   G-elis). 

This  process,  which  is  principally  applicable  to  alkaline  cyanides, 
depends  on  the  fact,  that  when  a  solution  of  iodine  is  added  to  one 


§    56.  FEREOCYANIDES.  175 

of  potassic  cyanide,  the  iodine  loses  its  colour  so  long  as  any 
undecomposed  cyanide  remains.  The  reaction  may  be  expressed 
by  the  following  formula  :  — 


Therefore,  2  eq.  iodine  represent  1  eq.  cyanogen  in  combination;  so 
that  1  c.c.  of  —  iodine  expresses  the  half  of  ^^3  eq.  cyanogen 
or  its  compounds.  The  end  of  the  reaction  is  known  by  the 
yellow  colour  of  the  iodine  solution  becoming  permanent. 

Commercial  cyanides  are,  however,  generally  contaminated  with 
caustic  or  monocarbonate  alkalies,  which  would  equally  destroy 
the  colour  of  the  iodine  as  the  cyanide  ;  consequently  these  must 
be  converted  into  bicarbonates,  best  done  by  adding  carbonic  acid 
water  (ordinary  soda  water). 

Example  :  5  gm.  of  potassic  cyanide  were  weighed  and  dissolved  in  500  c.c. 
water;  then  10  c.c.  (=0'1  gm.  cyanide)  taken  with  a  pipette,  diluted  with 
about  -j  liter  of  water,  100  c.c.  of  soda  water  added,  then  ^  iodine  delivered 
from  the  burette  until  the  solution  possessed  a  slight  but  permanent  yellow 
colour  ;  25'5  c.c.  were  required,  which  multiplied  by  0'003255  gave  0'08300 
gm.  instead  of  O'l  gm.,  or  83  per  cent,  real  cyanide.  Sulphides  must  of 
course  be  absent. 

4.     By  JQ   Silver   and   Chromate   Indicator. 

Vielhaber  (Arch.  Pliarm.  [3]  xiii.  408)  has  shown  that  weak 
solutions  of  prussic  acid,  such  as  bitter-almond  water,  etc.,  may  be 
readily  titrated  by  adding  magnesic  hydrate  suspended  in  water 
until  alkaline,  adding  a  drop  or  two  of  chromate  indicator,  and 
delivering  in  ~  silver  until  the  red  colour  appears,  as  in  the  case 
of  titrating  chlorides.  1  c.c.  silver  solution  =  0  '0027  gm.  HCy. 

This  method  may  be  found  serviceable  in  the  examination  of 
opaque  solutions  of  hydrocyanic  acid,  such  as  solutions  of  bitter- 
almond  oil,  etc.  ;  but  of  course  the  absence  of  chlorine  must  be 
insured,  or,  if  present,  the  amount  must  be  allowed  for. 

It  is  preferable  to  add  the  HCy  to  a  mixture  of  magnesia  and 
chromate,  then  immediately  titrate  Avith  silver. 


FERRO-    AND    FERRI-CYANIDES. 
Potassic    Ferrocyanide. 


Metallic  iron  x        7  '541  =  Crystallized  Potassic  ferrocyanide. 

Double  iron  salt       x        1-077=  „  „  „ 

1.      Oxidation    to    Ferricyanide    by    Permanganate    (De    Ha  en). 

§  56.     THIS  substance  may  be  estimated  by  potassic  permanga- 
nate, which  acts  by  converting  it  into  red  prussiate.     The  process 


1*76  VOLUMETEIC  ANALYSIS.  §    56. 

is  easy  of  application,  and  the  results  accurate.  A  standard 
solution  of  pure  ferrocyanide  should  be  used  as  the  basis  upon 
which  to  work,  but  can,  however,  be  dispensed  with,  if  the  operator 
chose  to  calculate  the  strength  of  his  permanganate  upon  iron  or  its 
compounds.  If  the  permanganate  is  decinormal,  there  is  of  course 
very  little  needed  for  calculation  (1  eq.  =  422  must  be  used  as  the 
systematic  number,  and  therefore  1  c.c.  of  y^-  permanganate  is 
equal  to  0*0422  gm.  of  yellow  prussiate).  The  standard  solution 
of  pure  ferrocyanide  contains  20  gm.  in  the  liter  :  each  c.c.  will 
contain  0-02  gm. 

The  Analysis  :  10  c.c.  of  the  standard  prussiate  solution  are  put  into  a 
white  porcelain  dish  or  beaker  standing  on  white  paper,  and  250  c.c.  or  so  of 
water  added ;  it  is  then  acidified  pretty  strongly  with  sulphuric  acid,  and  the 
permanganate  delivered  from  the  burette  until  a  pure  uranium  yellow  colour 
appears ;  it  is  then  cautiously  added  until  the  faintest  pink  tinge  occurs. 

Ferrocyanides  in  Alkali  waste. — Acidulate  the  solution  with 
HC1,  and  add  strong  bleaching  powder  solution  with  agitation  until 
a  drop  of  the  liquid  gives  no  blue  colour  with  ferric  indicator.  The 
liquid  is  then  titrated  with  a  solution  of  cupric  sulphate,  standardized 
on  pure  potassic  ferrocyanide,  using  dilute  ferrous  sulphate  as 
indicator;  as  soon  as  no  more  blue  or  grey  colour  occurs,  but 
a  faint  reddening,  the  process  is  ended. 

Ferrocyanides  in  Gas  Liquor. — 250  c.c.  are  evaporated  to  dryness, 
dissolved  in  water,  the  solution  filtered,  and  prussian  blue  precipitated 
by  ferric  chloride.  The  blue  is  filtered  off,  washed,  and  decomposed 
with  caustic  soda.  The  ferric  hydroxide  so  obtained  is,  after  filtering, 
washing,  and  dissolving  in  dilute  H2S04  reduced  with  zinc,  and 
titrated  with  permanganate.  Fe  x  5 '07  =  (NH4)4FeCy6. 


POTASSIC    FEBRICYANIDE. 

K6Cy12Fe2=658. 

Metallic  iron  x        5 '88          =  Potassic  ferricyanide. 

Double  iron  salt  x        1-68          =        ,,  „ 

^  Thiosulphate  x        0'0329      = 

2.      By    Iodine    and    Thiosulphate. 

This  salt  can  be  estimated  either  by  reduction  to  ferrocyanide 
and  titration  with  permanganate  or  bichromate  as  above,  or  by 
Lenssen's  method,  which  is  based  upon  the  fact,  that  when 
potassic  iodide  and  ferricyanide  are  mixed  with  tolerably  concen- 
trated hydrochloric  acid,  iodine  is  set  free. 

K6Fe2Cy12  +  2KI  =  2K4Cy6Fe  + 12 
the  quantity  of  which  can  be  estimated  by  ~  thiosulphate  and 


uy£ft 

§56.  SULPHOCYANIDES.  177 

starch.  This  method  does  not,  however,  give  the  most  satis- 
factory results,  owing  to  the  variation  produced  by  working 
with  dilute  or  concentrated  solutions.  C.  Mohr's  modification 
(see  Zinc,  §  78.1)  is,  however,  more  accurate,  and  is  as  follows  : — 
The  ferricyanide  is  dissolved  in  a  convenient  quantity  of  water, 
potassic  iodide  in  crystals  added,  together  with  hydrochloric  acid 
in  tolerable  quantity,  then  a  solution  of  pure  zinc  sulphate  in 
excess ;  after  standing  a  few  minutes  to  allow  the  decomposition  to 
perfect  itself,  the  excess  of  acid  is  neutralized  by  sodic  carbonate,  so 
that  the  latter  slightly  predominates. 

At  this  stage  all  the  zinc  ferricyanide  first  formed  is  converted 
into  the  ferrocyanide  of  that  metal,  and  an  equivalent  quantity  of 
iodine  set  free,  which  can  at  once  be  titrated  with  -f$  thiosulphate 
and  starch,  and  with  very  great  exactness.  1  c.c.  -^  thiosulphate 
=  0*0329  gm.  potassic  ferricyanide. 

The  mean  of  five  determinations  made  by  Mohr  gave  100*21 
instead  of  100. 

Another  method  consists  in  boiling  with  excess  of  potash,  then 
cooling,  and  adding  H202  till  the  colour  is  yellow.  The  excess  of 
the  peroxide  is  then  boiled  off,  H2S04  added,  and  titrated  with 
permanganate. 

3.      Reduction    of   Ferri-    to    Ferro-cyanide. 

This  process  is,  of  course,  necessary  when  the  determination  by 
permanganate  has  to  be  made,  and  is  best  effected  by  boiling  the 
weighed  ferricyanide  with  an  excess  of  potash  or  soda,  and  adding 
small  quantities  of  concentrated  solution  of  ferrous  sulphate  until 
the  precipitate  which  occurs  possesses  a  blackish  colour  (signifying 
that  the  magnetic  oxide  is  formed).  The  solution  is  then  diluted 
to  a  convenient  quantity,  say  300  c.c.,  well  mixed  and  filtered 
through  a  dry  filter;  50  or  100  c.c.  may  then  be  taken,  sulphuric 
acid  added,  and  titrated  with  permanganate  as  before  described. 

Other  soluble  ferro-  or  ferri-cyanides  may  be  examined  in  the  same 
way  as  the  potassium  salts,  and  if  insoluble,  they  may  generally 
be  converted  into  the  latter  by  boiling  with  strong  caustic  potash. 

SULPHOCYANIDES. 

For  the  estimation  of  sulphocyanic  acid  in  combination  with  the 
alkaline  or  earthy  bases,  Barnes  and  Liddle  (/.  S.  C.  I.  ii.  122) 
have  devised  a  method  which  is  easy  of  application,  and  gives  good 
technical  results.  It  is  not,  however,  available  for  gas  liquors. 

The  method  depends  upon  the  fact  that  when  a  solution  of 
a  cupric  salt  is  added  to  a  solution  of  a  sulphocyanide  in  presence 
of  a  reducing  agent,  as  sodic  bisulphite,  the  insoluble  cuprous  salt 
of  sulphocyanic  acid  is  precipitated,  the  end  of  the  reaction  being 
ascertained  by  a  drop  of  the  solution  in  the  flask  giving  a  brown 

N 


178  VOLUMETRIC  ANALYSIS.  §    57. 

colouration  when  brought  in  contact  with  a  drop  of  ferrocyanide. 
The  following  reactions  take  place  :  — 

2CuS04  +  2KSCN  +  Na2S03  +  IPO  = 
Cu2S2C2N2  +  K2S04  +  21STaHS04 
and 


The  following  solutions  are  required  :  — 

1.  A  standard  solution  of  Cupric  sulphate  containing  6*2375 
gm.  per  liter,  1  c.c.  of  which  is  equivalent  to  0*00145  gm.  SON. 

2.  A  solution  of  Sodic  bisulphite  of  specific  gravity  1  '3. 

3.  A  solution  of  Potassic  ferrocyanide  (1   :  20). 

The  Analysis  :  About  3  gm.  of  the  sample  are  weighed  from  a  stoppered 
tube  into  a  liter  flask,  dissolved  in  water,  and  made  up  to  the  mark.  After 
well  mixing,  25  c.c.  are  measured  into  a  flask,  about  3  c.c.  of  the  bisulphite 
added,  and  the  whole  boiled.  Whilst  this  is  heating  a  burette  is  filled  with 
the  copper  solution,  and  a  white  porcelain  slab  is  dotted  over  with  the 
ferrocyanide.  When  the  liquid  in  the  flask  has  reached  the  boiling  point, 
20  c.c.  of  the  copper  solution  are  run  in,  well  shaken,  the  precipitate  allowed 
to  settle  for  about  a  minute,  a  drop  is  taken  out  by  means  of  a  glass  rod,  and 
brought  in  contact  with  a  drop  of  ferrocyanide,  and  should  no  brown 
colouration  appear,  more  of  the  copper  solution  is  run  in,  say  1  c.c.  at  a 
time,  and  again  tested.  This  is  continued  until  a  drop  gives  an  immediate 
colour.  By  this  means  an  approximation  to  the  truth  is  obtained.  It  will 
be  observed,  during  a  titration,  that  the  mixed  drops,  after  standing  for  a 
minute,  or  even  less,  produce  a  brown  tint.  It  is  of  the  utmost  importance 
that  the  colouration  be  immediate. 

A  second  25  c.c.  of  the  sulphocyanide  solution  are  run  into  a  clean  flask, 
the  bisulphite  added,  and  boiled  as  before. 

Suppose  that  in  the  first  experiment,  after  an  addition  of  27  c.c.  of  copper 
solution,  no  colour  was  formed  with  ferrocyanide,  but  that  28  c.c.  gave  an 
immediate  colour  ;  then  in  the  second  experiment  27  c.c.  are  run  in  at  once, 
and  the  liquid  is  again  tested,  when  no  colour  should  appear.  The  copper 
solution  is  then  run  in  drop  by  drop  until  there  is  a  slight  excess  of  copper, 
as  proved  by  the  delicate  reaction  with  the  ferrooyanide.  The  second 
experiment  is  thus  rendered  more  exact  by  the  experience  gained  in  the  first. 

GOLD. 

Au  =  196-5. 
1  c.c.  or  1  dm.  normal  oxalic  acid  =  0*0655  gm.  or  0*655  grn.  Gold. 

§  57.  THE  technical  assay  of  gold  for  coining  purposes  is 
invariably  performed  by  cupellation.  Terchloride  of  gold  is, 
however,  largely  used  in  photography  and  electro-gilding,  and 
therefore  it  may  be  necessary  sometimes  to  ascertain  the  strength 
of  a  solution  of  the  chloride,  or  its  value  as  it  occurs  in  commerce. 

If  to  a  solution  of  gold  in  the  form  of  chloride  (free  from  nitric 
acid)  an  excess  of  oxalic  acid  be  added,  in  the  course  of  from 
eighteen  to  twenty-four  hours  all  the  gold  will  be  precipitated  in 
the  metallic  form,  while  the  corresponding  quantity  of  oxalic  acid 


§  58.  IODINE.  179 

lias  been  dissipated  in  the  form  of  carbonic  acid ;  if,  therefore,  the 
quantity  of  oxalic  acid  originally  added  be  known,  and  the  excess, 
after  complete  precipitation  of  the  gold,  be  found  by  permanganate, 
the  amount  of  gold  will  be  obtained. 

Example:  A  15-grain  tube  of  the  chloride  of  gold  of  commerce  was 
dissolved  in  water,  and  the  solution  made  up  to  300  decems.  20  dm.  of 
normal  oxalic  acid  were  then  added,  and  the  flask  set  aside  for  twenty-four 
liours  in  a  warm,  dark  place ;  at  the  end  of  that  time  the  gold  had  settled, 
and  the  supernatant  liquid  was  clear  and  colourless.  100  dm.  were  taken 
out  with  a  pipette,  and  titrated  with  •£$  permanganate,  of  which  25  dm.  were 
required;  this  multiplied  by  3  gives  75  dm.  =  7' 5  dm.  normal  oxalic  acid, 
which  deducted  from  the  20  dm.  originally  added,  left  12'5  dm.;  this 
multiplied  by  i  the  equivalent  of  gold  (1  eq.  of  gold  chloride  decomposing 
3  eq.  oxalic  acid)=0'655  gave  8' 195  grn.  metallic  gold,  or  multiplied  by  101 
(=  i.  eq.  AuCP)  gave  12*625  grn. ;  the  result  was  84  per  cent,  of  chloride  of 
gold  instead  of  100. 

IODINE. 
1  =  126-5. 

1.      By    Distillation. 

§  58.  FREE  iodine  is  of  course  very  readily  estimated  by  solution 
in  potassic  iodide,  and  titration  with  starch  and  •£$  thiosulphate, 
as  described  in  §  34.* 

Combined  iodine  in  haloid  salts,  such  as  the  alkaline  iodides, 
must  be  subjected  to  distillation  with  hydrochloric  acid,  and  some 
other  substance  capable  of  assisting  in  the  liberation  of  free  iodine, 
which  is  received  into  a  solution  of  potassic  iodide,  and  then 
titrated  with  ^  thiosulphate  in  the  ordinary  way.  Such  a 
substance  presents  itself  best  in  the  form  of  ferric  oxide,  or  some 
of  its  combinations ;  if,  therefore,  hydriodic  acid,  or  what  amounts 
to  the  same  thing,  an  alkaline  iodide,  be  mixed  with  an  excess  of 
ferric  oxide  or  chloride,  and  distilled  in  the  apparatus  shown  in 
fig.  29  or  30,  the  following  reaction  occurs  : — 

Fe203  +  2IH  =  2FeO  +  H20  + 12. 

The  best  form  in  which  to  use  the  ferric  oxide  is  iron  alum. 

The  iodide  and  iron  alum  being  brought  into  the  little  flask, 
fig.  30,  sulphuric  acid  of  about  1/3  sp.  gr.  is  added,  and  the 
cork  carrying  the  still  tube  inserted.  This  tube  is  not  carried  into 
the  solution  of  potassic  iodide  in  this  special  case,  but  within  a 
short  distance  of  it ;  and  the  end  must  not  be  drawn  out  to  a  fine 
point,  as  there  represented,  but  cut  off  straight.  The  reason  for 

*  I  would  here  again  impress  upon  the  operator's  notice  that  it  is  of  great  importance 
to  ascertain  the  exact  strength  of  the  standard  solutions  of  iodine  and  thiosulphate  as 
compared  with  each  other.  Both  solutions  constantly  undergo  an  amount  of  change 
depending  upon  the  temperature  at  which  they  are  kept,  their  exposure  to  light,  etc., 
and  therefore  it  is  absolutely  necessary,  to  ensure  exactness  in  the  multifarious  analyses 
which  can  be  made  by  the  aid  of  these  two  reagents,  to  verify  their  agreement  by 
weighing  a  small  portion  of  pure  dry  iodine  at  intervals,  and  titrating  it  with  the 
standard  thiosulphate. 

N    2 


180  VOLUMETRIC  ANALYSIS.  §    58. 

this  arrangement  is,  that  it  is  not  a  chlorine  distillation  for  the 
purpose  of  setting  iodine  free  from  the  iodide  solution,  as  is  usually 
the  case,  but  an  actual  distillation  of  iodine,  which  would  speedily 
choke  up  the  narrow  point  of  the  tube,  and  so  prevent  the  further 
progress  of  the  operation. 

As  the  distillation  goes  on,  the  steam  washes  the  condensed 
iodine  out  of  the  tube  into  the  solution  of  iodide,  which  must  be 
present  in  sufficient  quantity  to  absorb  it  all.  When  no  more- 
violet  vapours  are  to  be  seen  in  the  flask,  the  operation  is  ended  ; 
but  to  make  sure,  it  is  well  to  empty  the  solution  of  iodine  out 
of  the  condensing  tube  into  a  beaker,  and  put  a  little  fresh  iodide 
solution  with  starch  in,  then  heat  the  flask  again;  the  slightest 
traces  of  iodine  may  then  be  discovered  by  the  occurrence  of  the 
blue  colour  when  cooled.  In  case  this  occurs  the  distillation 
is  continued  a  little  while,  then  both  liquids  mixed,  and  titrated 
with  -^j-  thiosulphate  as  usual. 

In  a  note  on  page  151  it  is  stated  that  the  rubber  joints  to  the 
special  apparatus  of  Fresenius,  Bunsen,  or  M;ohr  for  iodine 
distillations  are  objectionable.  Topf  avoids  this  by  fitting  his 
apparatus  together,  so  that  although  rubber  is  used,  the  reagents 
do  not  come  in  contact  with  it  (Z.  a  C.  xxvi.  293). 

Another  form  of  apparatus  designed  by  Stortenbeker  (Z.  a  C. 
xxix.  273)  is  shown  in  fig.  34,  in  which  rubber  joints  are 
entirely  dispensed  with,  and  glass  connections  used.  The  con- 
nection between  the  distilling  tube  and  the  absorbing  apparatus  is 
a  water  joint,  the  tube  resting  in  a  socket  kept  wet  with  water, 
the  chloride  of  calcium  tube  is  filled  with  glass  pearls,  moistened 
with  concentrated  solution  of  potassic  iodide,  and  the  connection 
with  the  absorbing  apparatus  is  ground  in  like  an  ordinary  stopper. 
The  absorbing  bulbs  are  immersed  in  water  to  the  middle  of  the 
bulbs,  and  the  iodide  solution  filled  to  the  lower  end  of  them. 


Fig.  34. 


§    58.  IODINE.  181 

Ferric  chloride  may  be  used  instead  of  the  iron  alum,  but  it 
must  be  free  from  nitric  acid  or  active  chlorine  (best  prepared 
from  dry  Fe203  and  HC1). 

The  iodides  of  silver,  mercury,  and  copper  cannot  be  accurately 
analyzed  in  this  way,  but  must  be  specially  treated.  They  should 
be  dissolved  in  the  least  possible  quantity  of  sodic  thiosulphate 
solution,  and  precipitated  boiling  with  sodic  sulphide,  then  filtered ; 
the  filtrate  contains  the  whole  of  the  iodine  free  from  metal.  The 
filtrate  is  evaporated  to  dryness  and  ignited,  then  dissolved  in 
water,  and  distilled  with  a  good  excess  of  ferric  salt  (Mensel, 
Z.  a.  C.  xii.  137). 

2.     Mixtures   of   Iodides,    Bromides,    and   Chlorides. 

Donath  (Z.  a.  C.  xix.  19)  has  shown  that  iodine  may  be 
accurately  estimated  by  distillation  in  the  presence  of  other  halogen 
salts,  by  means  of  a  solution  containing  about  2  to  3  per  cent,  of 
chromic  acid,  free  from  sulphuric  acid. 

In  the  case  of  iodides  and  chlorides  together  the  action  is 
perfectly  regular,  and  the  whole  of  the  iodine  may  be  received  into 
potassic  iodide  without  any  interference  from  the  chlorine. 

In  the  case  of  bromides  being  present,  the  chromic  solution  must 
be  rather  more  dilute,  and  the  distillation  must  not  be  continued 
more  than  two  or  three  minutes  after  ebullition  has  commenced, 
otherwise  a  small  amount  of  bromide  is  decomposed. 

The  reaction  in  the  case  of  potassic  iodide  may  be  expressed 
thus : — 

6KI  +  8Cr03  =  P  +  Cr203  +  3K2Cr207. 

The  distillation  may  be  made  in  Mohr's  apparatus  (fig.  30), 
using  about  50  c.c.  of  chromic  solution  for  about  0'3  gm.  I. 

The  titration  is  made  with  thiosulphate  in  the  usual  way. 

A  much  less  troublesome  method  of  estimating  iodine  in  the 
presence  of  bromides  or  chlorides  has  been  worked  out  by  Cook 
(/.  C.  S.  1885,  471),  and  depends  on  the  fact  that  hydrogen 
peroxide  liberates  iodine  completely  from  an  alkaline  base  in  the 
presence  of  excess  of  acetic  acid,  while  neither  bromine  nor 
chlorine  are  affected. 

Hydrogen  peroxide  alone  will  only  partially  liberate  iodine  from 
potassic  iodide,  but  with  excess  of  a  weak  organic  acid  to  combine 
with  the  alkaline  hydroxide,  the  liberation  is  complete.  Strong 
mineral  acids  must  not  be  used,  or  bromine  and  chlorine,  if  present, 
would  also  be  set  free. 

The  Analysis :  The  solution  is  strongly  acidified  with  acetic  acid,  and 
sufficient  hydrogen  peroxide  added  to  liberate  the  iodine  (5  c.c.  will  suffice 
for  1  gm.  KI).  The  mixture  is  allowed  to  stand  from  half  an  hour  to 
an  hour ;  the  whole  of  the  iodine  separates,  some  being  in  the  solid  state 
if  the  quantity  is  considerable.  Chloroform  is  now  added  in  sufficient 
volume  to  dissolve  the  iodine,  the  solution  syphoned  off,  and  the  globule 


182  VOLUMETRIC  ANALYSIS.  .§    58. 

repeatedly  washed  with  small  quantities  of  water  to  remove  excess  of  peroxide, 
then  titrated  with  thiosulphate,  with  or  without  starch,  in  the  usual  way. 
If  the  peroxide  is  not  completely  removed  by  washing,  it  will  decompose  tlio 
sodic  iodide  produced  in  the  titration,  and  so  liberate  traces  of  iodine. 

The  results  obtained  by  Cook  in  mixtures  of  bromides,  iodides, 
and  chlorides,  were  about  99  per  cent,  of  the  iodine  present. 

Gooch  and  Browning  (Amer.  Journ.  Science,  xxxix.  March 
1890,  also  C.  N.  Ixi.  279)  publish  a  method  of  estimating  iodine 
in  halogen  salts  of  the  alkalies  which  gives  excellent  results,  and 
which  is  based  on  the  fact  that  arsenic  acid  in  strongly  acid  solution 
liberates  iodine,  becoming  itself  reduced  to  arsenious  acid,  according 
to  the  equation 

IPAsO4  +  2HI  =  H3As03  +  H20  +  21. 

A  very  careful  series  of  experiments  are  detailed  in  the  original 
paper,  the  outcome  of  the  whole  being  summarized  in  the  following- 
process  : — 

The  Analysis :  The  substance  (which  should  not  contain  of  chloride  more 
than  an  amount  corresponding  to  0*5  gm.  of  sodic  chloride,  nor  of  bromide 
more  than  corresponds  to  0'5  gm.  of  potassic  bromide,  nor  of  iodide  much 
more  than  the  equivalent  of  0*5  gm.  of  potassic  iodide)  is  dissolved  in  water 
in  an  Erlenmeyer  beaker  of  300  c.c.  capacity,  and  to  the  solution  are 
added  2  gm.  of  potassic  binarseniate  dissolved  in  water,  and  20  c.c.  of  a 
mixture  of  sulphuric  acid  and  water  in  equal  volumes,  and  enough  water  to 
increase  the  total  volume  to  100  c.c.  or  a  little  more.  A  platinum  spiral  is 
introduced,  a  trap  made  of  a  straight  two-bulb  drying  tube,  cut  off  short,  is 
hung  with  the  larger  end  downward  in  the  neck  of  the  flask,  and  the  liquid 
is  boiled  until  the  level  reaches  a  mark  put  upon  the  flask  to  indicate  a 
volume  of  35  c.c.  Great  care  should  be  taken  not  to  press  the  concentration 
beyond  this  point  on  account  of  the  double  danger  of  losing  arsenious 
chloride  and  setting  up  reduction  of  the  arseniate  by  the  bromide.  On  the 
other  hand,  though  35  c.c.  is  the  ideal  volume  to  be  attained,  failure  to 
concentrate  below  40  c.c.  introduces  no  appreciable  error.  The  liquid 
remaining  is  cooled  and  nearly  neutralized  by  sodic  hydrate  (ammonia  is  not 
equally  good),  neutralization  is  completed  by  potassic  bicarbonate,  an  excess 
of  20  c.c.  of  the  saturated  solution  of  the  latter  is  added,  and  the  arsenious 
oxide  in  solution  is  titrated  by  standard  iodine  in  the  presence  of  starch. 

With  ordinary  care  the  method  is  rapid,  reliable,  and  easily 
executed,  and  the  error  is  small.  In  analyses  requiring  extreme 
accuracy,  all  but  accidental  errors  may  be  eliminated  from  the 
results  by  applying  the  corrections  indicated. 

The  indicated  corrections  are  based  on  a  long  series  of  ex- 
periments, which  cannot  well  be  given  here,  but  the  results  may 
be  stated  shortly  as  follows: — 

When  no  chloride  or  bromide  is  present  the  iodine  may  be 
estimated  with  a  mean  error  of  0'2  m.gm.  in  0*5  gm.  or  so  of  the 
alkaline  iodide.  When  sodic  chloride  is  present  there  is  a  slight 
deficiency  in  iodine,  which  is  proportional  to  the  amount  of  iodide 
decomposed.  For  about  0*56  gm.  of  potassic  iodide  and  0'5  gm. 
of  sodic  chloride  the  deficiency  in  iodine  amounted  to  O'OOll  gm. 
When  the  iodide  is  decreased,  say  to  one-tenth  or  less,  the  deficiency 


§  58.  IODINE.  183 

falls  to  0*0002  gm.  The  presence  of  potassic  bromide  liberates 
traces  of  bromine,  and  consequently  increases  the  AsO3,  and  gives 
apparent  excess  of  iodine,  the  mean  error  being  0*0008  gm.  for 
0*5  gm.  of  bromide. 

The  simultaneous  action  of  the  chloride  and  bromide  tends  of 
course  to  neutralize  the  error  due  to  each.  Thus,  in  a  mixture 
weighing  about  1*5  gm.  and  consisting  of  sodic  chloride,  potassic 
bromide,  and  potassic  iodide  in  equal  parts,  the  mean  error  amounts 
to  -0*0003  gm.  The  largest  error  in  the  series  is  +  0*0016  gm., 
Avheii  the  bromide  was  at  its  maximum,  and  no  chloride  was 
present;  and  the  next  largest  was  -  0*0013  gm.,  when  the  chloride 
was  at  its  maximum  and  no  bromide  was  present. 

From  a  series  of  experiments  detailed  in  the  original  paper,  it 
was  deduced  that  the  amount  of  iodine  to  be  added,  in  each  case, 
may  be  obtained  by  multiplying  the  product  of  the  weights  in 
grams  of  sodic  chloride  and  potassic  iodide  by  the  constant  0*004 ; 
and  the  amount  to  be  subtracted,  by  multiplying  the  weight  in 
grams  of  potassic  bromide  by  0*0016 ;  but  in  order  to  make  use 
of  these  corrections,  the  approximate  amounts  of  these  salts  must 
be  known. 


3.     Titration  -with.   JQ   Silver   and   Sulphocyanate. 

The  sulphocyanate  and  silver  solutions  are  described  in  §  39. 

The  iodide  is  dissolved  in  300  or  400  times  its  weight  of  water 
in  a  well-stoppered  flask,  and  -£$  silver  delivered  in  from  the  burette 
with  constant  shaking  until  the  precipitate  coagulates,  showing 
that  silver  is  in  excess.  Ferric  indicator  and  nitric  acid  are  then 
added  in  proper  proportion,  and  the  excess  of  silver  estimated 
by  sulphocyanate  as  described  in  §  39. 


4.    Oxidation  of  combined  Iodine  by  Chlorine  (G-olfier  Besseyre 
and  Dupre). 

This  wonderfully  sharp  method  of  estimating  iodine  depends 
upon  its  conversion  into  iodic  acid  by  free  chlorine.  When  a 
solution  of  potassic  iodide  is  treated  with  successive  quantities  of 
chlorine  water,  first  iodine  is  liberated,  then  chloride  of  iodine 
(IC1)  formed.  If  starch,  chloroform,  benzole,  or  bisulphide  of 
carbon  be  added,  the  first  will  be  turned  blue,  while  any  of  the 
others  will  be  coloured  intense  violet.  A  further  addition  of  chlorine, 
in  sufficient  quantity,  produces  pentachloride  of  iodine  (IC15),  or 
rather,  as  water  is  present,  iodic  acid  (I03H).  No  colouration  of 
the  above  substances  is  produced  by  these  compounds,  and  the 
accuracy  with  which  the  reaction  takes  place  has  been  made  use  of 
byGolfier  Besseyre  and  Dupre,  independently  of  each  other, 
for  the  purpose  of  estimating  iodine.  The  former  suggested  the  use 


184  VOLUMETRIC  ANALYSIS.  §    58. 

of  starch,  the  latter  chloroform  or  benzole,  with  very  dilute  chlorine 
water.     Dupre's  method  is  preferable  on  many  accounts. 

Example:  30  c.c.  of  weak  chlorine  water  were  put  into  a  beaker  with 
potassic  iodide  and  starch,  and  then  titrated  with  ^  thiosulphate,  of  which 
17  c.c.  were  required. 

10  c.c.  of  solution  of  potassic  iodide  containing  O'OIO  gin.  of  iodine  were 
put  into  a  stoppered  bottle,  chloroform  added,  and  the  same  chlorine  water  as 
above  delivered  in  from  the  burette,  with  constant  shaking,  until  the  red 
colour  of  the  chloroform  had  disappeared ;  the  quantity  used  was  85'8  c.c. 
The  excess  of  chlorine  was  then  ascertained  by  adding  sodic  bicarbonate, 
potassic  iodide,  and  starch.  A  slight  blue  colour  occurred ;  this  was  removed 
by  TW  thiosulphate,  of  which  T2  c.c.,was  used.  Now,  as  30  c.c.  of  the 
chlorine  solution  required  17  c.c.,  the  85'8  c.c.  required  48'62  c.c.  of  thio- 
sulphate. From  this,  however,  must  be  deducted  the  1'2  c.c.  in  excess, 
leaving  47'42  c.c.  T^r=4'742  c.c.  of  ^  solution,  which  multiplied  by  0'00211, 
the  one-sixth  of  10ft00  eq.  (1  eq.  of  iodic  acid  liberating  6  eq.  iodine),  gave 
0*010056  gin.  iodine  instead  of  O'Ol  gm. 

Mohr  suggests  a  modification  of  this  method,  which  dispenses 
with  the  use  of  chloroform,  or  other  similar  agent. 

The  weighed  iodine  compound  is  brought  into  a  stoppered  flask,  and 
chlorine  water  delivered  from  a  large  burette  until  all  yellow  colour  has 
disappeared.  A  drop  of  the  mixture  brought  in  contact  with  a  drop 
of  starch  must  produce  no  blue  colour;  sodic  bicarbonate  is  then  added 
till  the  mixture  is  neutral  or  slightly  alkaline,  together  with  potassic  iodide 
and  starch ;  the  blue  colour  is  then  removed  by  ^  thiosulphate.  The 
strength  of  the  chlorine  water  being  known,  the  calculation  presents  no 
difficulty. 

Mohr  obtained  by  this  means  0*010108  gm.  iodine,  instead  of 
1-01  gm. 

5.     Oxidation  by  Permanganate    (Beinige). 

This  process  for  estimating  iodine  in  presence  of  bromides  and 
chlorides  gives  satisfactory  results. 

When  potassic  iodide  and  permanganate  are  mixed,  the  rose 
colour  of  the  latter  disappears,  a  brown  precipitate  of  manganic 
peroxide  results,  and  free  potash  with  potassic  iodate  remain  in 
solution.  1  eq.  1=  126'5  reacts  on  1  eq.  K2Mn208  =  316,  thus— 

KI  +  K2Mn208  =  KIO3  +  K20  +  2Mn02. 

Heat  accelerates  the  reaction,  and  it  is  advisable,  especially  with 
weak  solutions,  to  add  a  small  quantity  of  potassic  carbonate  to 
increase  the  alkalinity.  No  organic  matter  must  be  present. 

The  permanganate  and  thiosulphate  solutions  required  in  the 
process  may  conveniently  be  of  y^  strength,  but  their  reaction  upon 
each  other  must  be  definitely  fixed  by  experiment  as  follows : — 
2  c.c.  of  permanganate  solution  are  freely  diluted  with  water,  a  few 
drops  of  sodic  carbonate  added,  and  the  thiosulphate  added  in  very 
small  portions  until  the  rose  colour  is  just  discharged.  The  slight 


§  58.  IODINE.  185 

turbidity   produced   by  the   precipitation   of    hydrated   manganic 
oxide  need  not  interfere  with  the  observation  of  the  exact  point. 

The  Analysis :  The  iodine  compound  being  dissolved  in  water,  and  always 
existing  only  in  combination  with  alkaline  or  earthy  bases,  is  heated  to 
gentle  boiling,  rendered  alkaline  with  sodic  or  potassic  carbonate,  and 
permanganate  added  till  in  distinct  excess,  best  known  by  removing  the 
liquid  from  the  fire  for  a  minute,  when  the  precipitate  will  subside,  leaving 
the  upper  liquid  rose-coloured;  the  whole  may  then  be  poured  into  a  500-c.c. 
flask,  cooled,  diluted  to  the  mark,  and  100  c.c.  taken  out  for  titration  with 
thiosulphate.  The  amount  so  used,  being  multiplied  by  5,  will  give  the 
proportion  required  for  the  whole  liquid,  whence  can  be  calculated  the 
amount  of  iodine.  To  prove  the  accuracy  of  the  process  in  a  mixture  of 
iodides,  bromides,  and  chlorides,  with  excess  of  alkali,  the  following  experi- 
ment was  made.  7  gm.  commercial  potassic  bromide,  the  same  of  sodic 
chloride,  with  1  gm.  each  of  potassic  hydrate  and  carbonate,  were  dissolved 
in  a  convenient  quantity  of  water,  and  heated  to  boiling ;  permanganate  was 
then  added  cautiously  to  destroy  the  traces  of  iodine  and  other  impurities 
affecting  the  permanganate  so  long  as  decoloration  took  place ;  the  slightest 
excess  showed  a  green  colour  (manganate).  To  the  mixture  was  then  added 
01246  gm.  pure  iodine,  and  the  titration  continued  as  described :  the  result 
was  0125  gm.  I. 

With  systematic  solutions  of  permanganate  and  thiosulphate 
the  calculation  is  as  follows : — 

1  c.c.  ^  solution  =  0'01 265  gm.  I. 


6.     By  Nitrous  Acid  and   Carbon   Bisulphide    (Fresenius). 
This  process  requires  the  following  standard  solutions  : — 

(a)  Potassic  iodide,  about  5  gm.  per  liter. 

(b)  Sodic  thiosulphate,  -^  normal,  12 '4  gm.  per  liter,  or  there- 
about. 

(c)  Citrous  acid,  prepared  by  passing  the  gas  into  tolerably 
strong  sulphuric  acid  until  saturated. 

(d)  Pure  Carbon  bisulphide. 

(e)  Solution  of  Sodic  bicarbonate,  made  by  dissolving  5  gm.  of 
the  salt  in  1  liter  of  water,  and  adding  1  c.c.  of  hydrochloric  acid. 

The  strength  of  the  sodic  thiosulphate  in  relation  to  iodine  is 
first  ascertained  by  placing  50  c.c.  of  the  iodide  solution  into  a 
500  c.c.  stoppered  flask,  then  about  150  c.c.  water,  20  c.c.  carbon 
bisulphide,  then  dilute  sulphuric  acid,  and  lastly,  10  drops  of  the 
nitrous  solution.  The  stopper  is  then  replaced,  and  the  whole  well 
shaken,  set  aside  to  allow  the  carbon  liquid  to  settle,  and  the  super- 
natant liquid  poured  into  another  clean  flask.  The  carbon  bisul- 
phide is  then  treated  three  or  four  times  successively  with  water  in 
the  same  way  till  the  free  acid  is  mostly  removed,  the  washings 
being  all  mixed  in  one  flask;  10  c.c.  of  bisulphide  are  then  added 
to  the  washings,  well  shaken,  and  if  at  all  coloured,  the  same 
process  of  washing  is  carried  on.  Finally,  the  two  quantities  of 


186  VOLUMETRIC   ANALYSIS.  §    59. 

bisulphide  are  brought  upon  a  moistened  filter,  washed  till  free 
from  acid,  a  hole  made  in  the  filter,  and  the  bisulphide  which  now 
contains  all  the  iodine  in  solution  allowed  to  run  into  a  clean  small 
flask,  30  c.c.  of  the  sodic  bicarbonate  solution  added,  then  brought 
under  the  thiosulphate  burette,  and  the  solution  allowed  to  flow 
into  the  mixture  while  shaking  until  the  violet  colour  is  entirely 
discharged.  The  quantity  so  used  represents  the  weight  of  iodine 
contained  in  50  c.c.  of  the  standard  potassic  iodide,  and  may 
be  used  on  that  basis  to  ascertain  any  unknown  weight  contained  in 
a  similar  solution. 

When  very  small  quantities  of  iodine  are  to  be  titrated,  weaker 
solutions  and  smaller  vessels  may  be  used. 

7.      By    jo    Silver    Solution    and    Starch    Iodide    (Pisani). 

The  details  of  this  process  are  given  under  the  head  of  silver 
assay  (§  70.2),  and  are  of  course  simply  a  reversal  of  the  method 
there  given.  This  method  is  exceedingly  serviceable  for  estimating 
small  quantities  of  combined  iodine  in  the  presence  of  chlorides 
and  bromides,  inasmuch  as  the  silver  solution  does  not  react  upon 
these  bodies  until  the  blue  colour  is  destroyed. 

IRON. 

Fe=56. 

Factors. 

1  c.c.  — j-  permanganate,  bichromate, 

or  thiosulphate  =  0'0056  Fe 

=  0-0072  FeO 
=  0-0080  FeW 


ESTIMATION    IN    THE    FERROUS    STATE. 

1.     "Verification    of    the    standard    solutions    of    Permanganate    or 

Bichromate. 

§  59.  THE  estimation  of  iron  in  the  ferrous  state  has  already 
been  incidentally  described  in  §§  31,  32,  and  33.  The  present 
section  is  an  amplification  of  the  methods  there  given,  as  applied 
more  distinctly  to  ores  and  products  of  iron  manufacture  ;  but 
before  applying  the  permanganate  or  bichromate  process  to  these 
substances,  and  since  many  operators  prefer,  with  reason,  to 
standardize  such  solutions  upon  metallic  iron,  especially  for  use  in 
iron  analysis,  the  following  method  is  given  as  the  best : — 

A  piece  of  soft  iron  wire,  known  as  "  flower  "  wire,  is  well  cleaned  with 
scouring  paper,  and  about  1  gram  accurately  weighed ;  this  is  placed  into  a 
250  c.c.  boiling  flask  a,  and  100  c.c.  of  dilute  pure  sulphuric  acid  (1  part 
concentrated  acid  to  5  of  water)  poured  over  it;  about  a  gram  of  sodic 


§  59.  IKON.  187 

bicarbonate  is  then  added,  and  the  apparatus  fixed  together  as  in  fig  35,  the 
pinch-cock  remaining  open.  The  flask  a  is  closed  by  a  tight-fitting  india- 
rubber  stopper,  through  which  is  passed  the  bent  tube.  The  flask  c  contains 
20  or  30  c.c.  of  pure  distilled  water ;  the  flask  a  being  supported  over  a  lamp 
is  gently  heated  to  boiling,  and  kept  at  this  temperature  until  all  the  iron  is 
dissolved ;  meanwhile  about  300  c.c.  of  distilled  water  are  boiled  in  a  separate 
vessel  to  remove  all  air,  and  allowed  to  cool.  As  soon  as  the  iron  is  dissolved, 
the  lamp  is  removed,  and  the  pinch-cock  closed ;  when  cooled  somewhat,  the 
pinch-cock  is  opened,  and  the  wash  water  suffered  to  flow  back  together  with 
the  boiled  water,  which  is  added  to  it  until  the  flask  is  filled  nearly  to  the 
mark.  The  apparatus  is  then  disconnected,  and  the  flask  a  securely  corked 
with  a  solid  rubber  cork,  and  suffered  to  cool  to  the  temperature  of  the  room. 
Finally,  the  flask  is  filled  exactly  to  the  mark  with  the  boiled  water,  and  the 
whole  well  shaken  and  mixed.  When  the  small  portion  of  undissolved 
carbon  has  subsided,  50  c.c.,  equal  to  j  the  weight  of  iron  taken,  may  be 
removed  with  the  pipette  for  titration  with  the  permanganate  or  bichromate. 

In  the  case  of  permanganate  the  50  c.c.  are  freely  diluted  with  freshly 
boiled  and  cooled  distilled  water,  and  the  standard  solution  cautiously  added 
from  a  tap  burette,  divided  into  ^  c.c.,  until  the  rose  colour  is  faintly 
perceived. 

In  the  case  of  bichromate  the  solution  should  be  less  diluted,  and  the 
titration  conducted  precisely  as  in  §  33. 


Fig.  35. 


Instead  of  the  two  flasks,  many  operators  use  a  single  flask,  fitted 
with  caoutchouc  stopper,  through  which  a  straight  glass  tube  is 
passed,  fitted  with  an  india-rubber  slit  valve  (known  as  Buns  en's 
valve),  which  allows  gas  or  vapour  to  pass  out,  but  closes  by 
atmospheric  pressure  when  the  evolution  ceases. 

If  the  solution  of  permanganate  or  bichromate  have  been  carefully  pre- 
pared by  weighing  the  purest  reagents,  the  probability  is  that  they  will  be 
found  exact  in  the  titration  when  conducted  as  just  described,  allowing  for 
the  known  average  impurity  in  metallic  iron,  which  may  be  taken  at  04  per 
cent.;  but  in  order  to  be  absolutely  secure  in  the  working  power  of  the 
solution,  it  is  well  to  prove  them  thoroughly,  and  in  case  non-systematic 
solutions  are  used,  it  is  of  course  absolutely  necessary  to  do  so.  Therefore, 
supposing  that  1'050  gm.  of  iron  has  been  dissolved  as  above  described,  and 
the  mean  of  three  separate  titrations  has  shown  that  21'3  c.c.  of  permanganate 
or  bichromate  have  been  required,  the  amount  of  pure  iron  converted  by 
100  c.c.  of  standard  solution  is  found  as  follows: — -1-f-5-  =  0'210  gm.  of  iron 
wire,  but  as  this  is  not  pure  iron,  the  following  correction  is  necessary — 
0'210x  0*996= 0'20915  gm.,  which  is  the  actual  weight  of  pure  iron— hence 


188  VOLUMETRIC  ANALYSIS.  §    59. 

by  the  equation  21'3  c.c.  :  0'20915  gm.  :  :  100  c.c. :  x  gm.  =  0*98197  gm., 
therefore  100  c.c.  of  such  permanganate  represent  0'98197  gm.  pure  metallic 
iron. 

The  double  iron  salt  (p.  106)  is  a  most  convenient  material  for 
adjusting  standard  solutions,  but  it  must  be  most  carefully  made 
from  pure  materials,  dried  perfectly  in  the  granular  form,  and  kept 
from  the  light  in  small  dry  bottles,  well  closed.  In  this  state  it 
will  keep  for  years  unchanged,  and  only  needs  immediate  solution 
in  water  for  use.  Even  in  the  case  of  the  salt  not  being  strictly 
free  from  ferric  oxide,  due  to  faulty  preparation,  if  it  be  once 
thoroughly  dried,  and  kept  as  above  described,  its  actual  ferrous 
strength  may  be  found  by  comparison  with  metallic  iron,  and 
a  factor  found  for  weighing  it  in  system. 

One  cardinal  point  must  never  be  forgotten  ;  namely,  that  ferrous 
compounds  are  much  more  stable  in  sulphuric  than  in  hydrochloric 
acid  solution,  and  whenever  possible,  sulphuric  acid  should  be  used 
as  the  solvent.  When  hydrochloric  acid  must  be  used,  manganous 
or  magnesic  sulphate  should  invariably  be  added. 


2.    Direct  Estimation  of  the  Percentage  of  Pure  Iron  in  Steel,  Cast 
and  "Wroug-ht  Iron,  Spieg-eleisen,  Ores,  etc.  (Mohr's  Method). 

Instead  of  the  hitherto  common  method  of  separately  estimating 
the  impurities  in  samples  of  manufactured  iron  and  steel,  this 
process  is  adapted  to  the  delicate  estimation  of  the  iron  itself,  and 
is  similar  in  principle  to  the  assay  of  silver  by  Gay  L us  sac's 
method ;  that  is  to  say,  the  analysis  is  so  arranged  that  the  greatest 
accuracy  shall  be  secured. 

The  standard  solutions  of  potassic  bichromate,  of  which  there  are 
two,  are  so  prepared  that  100  c.c.  or  dm.  of  the  first  will  exactly 
convert  respectively  1  gm.  or  10  grains  of  iron  into  ferric  oxide  ;  the 
second,  or  decimal  solution,  is  one-tenth  the  strength  of  the  first. 

The  solution  of  bichromate  No.  1  is  prepared  by  dissolving  8 '7 7 2 
gm.  of  the  pure  salt  in  1  liter,  or  87 '72  grn.  in  10,000  grains  of 
distilled  water  at  16°  C.  The  decimal  solution  No.  2  is  made  by 
taking  100  c.c.  of  No.  1  and  diluting  it  to  1  liter,  or  100  decems  to 
10,000  grains  ;  therefore — 

1  c.c.  or  dm.  of  No.  1  =  0'01  gm.  or  O'l  grn.  iron. 
1  c.c.  or  dm.  of  No.  2  =  0'001  gm.  or  O'Ol  grn.  ditto. 

The  Analysis :  The  sample  of  iron  to  be  examined  is  reduced  to  powder  in 
a  hardened  steel  mortar,  or  if  in  the  form  of  wire,  or  in  a  soft  state,  cut  into 
small  pieces,  and  exactly  T05  gm.  or  10'5  grn.  weighed  off ;  this  is  brought 
into  the  apparatus  fig.  35,  or  some  similar  arrangement,  and  dissolved  in 
pure  hydrochloric  or  sulphuric  acid.  When  the  solution  is  accomplished 
100  c.c.  or  dm.  of  bichromate  solution  No.  1  (containing  0'8785  gm.  or 
8'758  grn.  of  bichromate,  which  is  exactly  sufficient  to  peroxide  respectively 
1  gm.  or  10  grn.  of  pure  iron)  are  added ;  the  decimal  solution  is  then  added 
from  a  small  burette,  until  a  drop  of  the  mixture  brought  in  contact  with 


§  59.  IKON.  189 

red  potassic  prussiate  no  longer  produces  a  blue  colour.     The  analysis  is 
then  calculated  in  the  usual  way. 

Example:  1'05  gm.  of  Bessemer  steel  was  dissolved  in  pure  sulphuric 
acid,  100  c.c.  of  bichromate  No.  1  added,  and  afterwards  39  c.c.  of  No.  2 
required  for  complete  oxidation ;  consequently  there  was  T039  gm.  of  pure 
iron  contained  in  the  1'050  gm.  taken  for  analysis.  This  is  equal  to  989'4 
parts  per  thousand,  or  98' 94  per  cent. 

Instead  of  the  empirical  solutions  here  described,  the  ordinary 
decinormal  and  centinormal  solutions  of  bichromate  or  perman- 
ganate may  be  employed  with  equal  accuracy.  As  100  c.c.  of 
decinormal  solution  are  equal  to  0'56  gm.  of  pure  iron,  it  is 
necessary  that  somewhat  more  than  this  quantity  of  the  sample 
should  be  weighed,  say  0*58  or  0*60  gm.  100  c.c.  of  decinormal 
solution  are  then  added,  and  the  analysis  completed  with  the 
centinormal  solution. 


3.      Reduction    of   Ferric    Compounds    to    the    Ferrous    State. 

This  may  be  accomplished  by  metallic  zinc  or  magnesium,  for  use  with 
permanganate,  or  by  stannous  chloride,  for  bichromate  solution.  Some 
operators  use  other  reducing  agents,  such  as  sodic  sulphite  or  thiosulphate, 
hydric  sulphide  or  ammonic  sulphide,  etc.,  but  the  zinc  or  tin  methods  are 
simpler  and  better.  The  magnesium  method  is  elegant  and  rapid  but  costly. 
In  the  case  of  zinc  being  used,  the  metal  must  either  be  free  from  iron,  or  if 
it  contain  any,  the  exact  quantity  must  be  known  and  allowed  for;  and 
further,  the  pieces  of  zinc  used  must  be  entirely  dissolved  before  the 
solution  is  titrated.*  In  the  case  of  stannous  chloride  the  solution  must  be 
clear,  and  is  best  made  to  contain  10  to  15  gm.  per  liter,  as  directed  in  §  33.2. 
The  point  of  exact  reduction  in  the  boiling  hot  liquid  may  be  known  very 
closely  by  the  discharge  of  colour  in  the  ferric  solution  ;  but  may  be  made 
sure  by  the  use  of  a  freshly  made  solution  of  potassic  sulphocyanide  spread  in 
drops  on  a  white  plate,  care  being  taken  to  lose  no  time  in  bringing  the  drop 
of  iron  solution  in  contact  with  the  test,  in  order  to  avoid  re-oxidation  from 
the  air.  The  occurrence  of  a  faint  pink  tinge  may  be  accepted  as  an  evidence 
of  the  proper  point.  When  this  occurs,  two  or  three  drops  of  the  standard 
bichromate  may  be  added  to  the  solution,  and  another  test  made ;  if  this 
shows  a  slight,  but  nevertheless  distinct,  accession  of  colour  with  the 
sulphocyanide,  the  absence  of  stannous  salt  in  excess  is  proved,  and  the 
titration  should  be  commenced  at  once. 

When  bichromate  is  used,  Atkinson  ((7.  N.  xlvi.  217)  strongly 
recommends  the  use  of  ammonic  bisulphite  as  the  reducing  agent, 
and  discourages  the  use  of  stannous  chloride,  owing  to  the  liability 
to  error  from  excess  or  deficiency  of  the  reagent.  He  also  points 

*  Many  operators  now  use  amalgamated  zinc  in  conjunction  with  platinum  foil  for 
the  reduction,  hut  a  practical  difficulty  occurs  from  the  platinum  becoming  also 
amalgamated  through  contact  with  the  zinc  and  stopping  the  action.  Beebe 
(C.  N.  liii.  269)  suggests  the  following  convenient  arrangement :—  A  strip  of  thin, 
platinum  foil,  1  in.  square,  is  perforated  with  pin  holes  all  over,  then  hent  into  a, 
(J  form,  and  the  ends  connected  with  platinum  wire  so  as  to  form  a  basket.  In  this  is 
placed  a  piece  of  amalgamated  zinc,  and  the  whole  suspended  by  a  stout  platinum  wire 
in  the  reducing  flask.  When  lowered  into  the  solution,  another  strip  of  platinum  foil, 
2  in.  square,  is  dropped  in  and  leaned  against  the  wire  carrying  the  basket :  a  very  free 
evolution  of  hydrogen  is  then  obtained  from  the  foil.  When  the  reduction  is  complete, 
the  basket  is  lilted  out  and  well  washed  into  the  beaker  containing  the  liquid  to  be 
titrated. 


190  VOLUMETRIC   ANALYSIS.  §    60. 

out  that  zinc  is  less  recommendable,  owing  to  its  interference  with 
the  colour  produced  with  the  indicator.  The  bisulphite  is  used  as 
follows: — To  the  acid  solution  of  the  ore  or  metal,  diluted  and 
filtered,  ammonia  is  added  until  a  faint  precipitate  of  ferric  oxide 
occurs.  This  is  re-dissolved  with  a  few  drops  of  HC1,  and  some 
strong  solution  of  bisulphite  added,  in  the  proportion  of  about 
1  c.c.  for  each  0*1  gm.  of  ore,  or  0'05  gm.  Fe.  The  mixture 
is  well  stirred,  boiling  water  added,  then  acidified  with  dilute 
sulphuric  acid,  and  boiled  for  half  an  hour :  it  is  then  ready  for 
titration. 

D.  J.  Carnegie  (/.  C.  S.  liii.  468)  points  out  the  value  of  zinc 
dust  for  the  rapid  reduction  of  ferric  solutions,  and  suggests  the 
following  method  of  carrying  it  out. 

The  bottom  of  a  dry  and  narrow  beaker  is  covered  with  zinc 
dust  sifted  through  muslin.  A  known  volume  of  ferric  solution, 
previously  nearly  neutralized  with  ammonia,  is  placed  in  the  beaker 
and  shaken  with  the  zinc  dust ;  then  a  known  volume  of  dilute 
sulphuric  acid  is  added  and  shaken  for  a  few  moments.  The 
reduction  is  much  more  rapid  in  neutral  than  in  acid  solutions,  but 
of  course  acid  in  this  case  must  be  present  in  excess  to  keep  the 
iron  in  solution.  Carnegie  withdraws  a  portion  of  the  reduced 
solution  from  the  undissolved  zinc  by  help  of  a  filter  such  as  is 
described  on  p.  18,  and  as  measured  volumes  have  been  used,  an 
aliquot  part  taken  with  a  pipette  may  be  at  once  titrated,  and  the 
amount  of  iron  found.* 

Clemens  Jones  in  a  paper  read  before  the  American  Institute  of 
Mining  Engineers,  and  which  is  reproduced  in  G.  N.  Ix.  93,  adopts 
the  plan  suggested  by  Carnegie,  and  has  designed  a  special 
apparatus  for  filtering  the  ferric  solution  through  a  column  of  zinc 
dust.  This  arrangement  gives  complete  reduction  in  a  very  short 
period  of  time,  and  is  serviceable  where  a  large  number  of  titrations 
have  to  be  carried  on. 


ESTIMATION    OF    IRON    IN    THE    FERRIC    STATE. 
1.     Direct   Titration   of  Iron   "by   Stannous   Chloride. 

§  60.  THE  reduction  of  iron  from  the  ferric  to  the  ferrous  state 
by  this  reagent  has  been  previously  referred  to;  and  it  will  be 
readily  seen  that  the  principle  involved  in  the  reaction  can  be  made 

*  Commercial  zinc  dust  is  probably  a  by-product  in  zinc  manufacture,  and  cannot 
therefore  be  obtained  pure.  Samples  examined  by  myself,  and  apparently  others  also, 
do  not,  however,  contain  much  iron,  but  a  good  deal  of  zinc  oxide  with  traces  of 
cadmium  and  lead.  Carnegie  states  that  the  oxide  maybe  removed  by  repeatedly 
digesting  with  weak  acid,  and,  still  better,  by  treatment  with  ammonic  chloride  and 
ammonia,  the  well-washed  dust  being  finally  dried  on  porous  tiles  in  a  vacuum. 
I  find  that  by  washing  once  with  strong  alcohol  after  the  water,  and  finally  with  ether, 
the  dust  may  be  rapidly  dried  in  good  condition,  and  when  a  quantity  of  such  purified 
dust  is  obtained,  its  amount  of  iron  may  easily  be  estimated  once  for  all,  and  allowed 
for  in  titration.  Good  zinc  dust  is  undoubtedly  a  valuable  reagent  in  a  laboratory  for 
other  purposes  beside  iron  titrations. 


§    60.  IRON.  191 

available  for  a  direct  estimation  of  iron,  being,  in  fact,  simply  a 
reversion  of  the  ordinary  process  by  permanganate  and  bichromate. 
Fresenius  has  recorded  a  series  of  experiments  made  on  the 
weak  points  of  this  process,  and  gives  it  as  his  opinion  that,  with 
proper  care,  the  results  are  quite  accurate.  The  summary  of  his 
process  is  as  follows  : — 

(a)  A  solution  of  ferric  oxide  of  known  strength  is  first  prepared  by 
dissolving  10'04  gm.  of  soft  iron  wire  ( =  10  gm.  of  pure  iron)  in  pure  hydro- 
chloric acid,  adding  potassic  chlorate  to  complete  oxidation,  boiling  till  the 
excess  of  chlorine  is  removed,  and  diluting  the  solution  to  1  liter.* 

(5)  A  clear  solution  of  stannous  chloride,  of  such  strength  that  about  one 
volume  of  it  and  two  of  the  iron  solution  are  required  for  the  complete 
reaction  (see  §  33.2). 

(c)  A  solution  of  iodine  in  potassic  iodide,  containing  about  O'OIO  gm. 
of  iodine  in  1  c.c.  (if  the  operator  has  the  ordinary  decinormal  iodine  solution 
at  hand,  it  is  equally  applicable).  The  operations  are  as  follows  : — 

(1)  1  or  2  c.c.  of  the  tin  solution  are  put  into  a  beaker  with  a  little  starch, 
and  the  iodine  solution  added  from  a  burette  till  the  blue  colour  occurs; 
the  quantity  is  recorded. 

(2)  50  c.c.  of  the  iron  solution  (=0'5  gm.  of  iron)  are  put  into  a  small 
flask  with  a  little  hydrochloric  acid,  and  heated  to  gentle  boiling  (preferably 
on  a  hot  plate) ;  the  tin  solution  is  then  allowed  to  flow  in  from  a  burette 
until  the  yellow  colour  of  the  solution  is  nearly  destroyed ;  it  is  then  added 
drop  by  drop,  waiting  after  each  addition  until  the  colour  is  completely 
gone,  and  the  reduction  ended.     If  this  is  carefully  managed,  there  need  be 
no  more  tin  solution  added  than  is  actually  required;  however,  to  guard 
against  any  error  in   this  respect,  the  solution  is  cooled,  a  little  starch 
added,  and  the  iodine  solution  added  by  drops  until  a  permanent  blue  colour 
is  obtained.     As  the  strength  of  the  iodine  solution  compared  with  the  tin 
has  been  found  in  1,  the  excess  of  tin  solution  corresponding  to  the  iodine 
used  is  deducted  from  the  original  quantity,  so  that  by  this  means  the  volume 
of  tin  solution  corresponding  to  0'5  gm.  of  iron  is  found. 

The  operator  is  therefore  now  in  a  position  to  estimate  any 
unknown  quantity  of  iron  which  may  exist  in  a  given  solution,  in 
the  ferric  state,  by  means  of  the  solution  of  tin.f 

If  the  iron  should  exist  partly  or  wholly  in  the  state  of  ferrous 
oxide,  it  must  be  oxidized  by  the  addition  of  potassic  chlorate,  and 
boiling  to  dissipate  the  excess  of  chlorine,  as  described  in  a,  or 
with  hydrogen  peroxide. 

Example .-  50  c.c.  of  iron  solution,  containing  0'5  gm.  of  iron,  required 
25  c.c.  of  tin  solution. 

A  solution  containing  an  unknown  quantity  of  iron  was  then  taken  for 

*  A  ferric  standard  may  also  be  made,  as  suggested  by  French.  (C.  N.  Ix.  271),  by 
dissolving  a  weighed  amount  of  double  iron  salt  in  dilute  sulphuric  acid,  adding  an 
excess  of  hydrogen  peroxide,  warming  up,  and  finally  boiling  to  dissipate  the  excess  of 
the  peroxide. 

fF.  H.  Morgan  (Jburn.  Anal.  CJiem.  ii.  169)  points  out  a  very  simple  and  useful 
method  of  finding  the  end-point  in  titrating  iron  solutions  with  stannous  chloride 
without  resorting  to  an  indicator.  It  consists  in  using  a  round  bottom  white  glass 
flask  containing  the  boiling  liquid  under  titration,  fixed  over  a  small  bluish-coloured 
Bunsen  flame  at  a  distance  of  13  m.m.  in  a  darkened  room  or  a  dark  corner.  So  long 
as  the  slightest  trace  of  unreduced  iron  exists,  a  distinct  green  colour  appears  when 
looking  at  the  faint  blue  flame  through  the  solution.  It  is  stated  that  one  part  of  iron 
as  oxide  may  be  recognized  in  1,500,000  parts  of  solution  by  this  means. 


192  VOLUMETRIC   ANALYSIS.  §    60. 

analysis,  which  required  20  c.c.,  consequently  a  rule-of-three  sum  gave  the 
proportion  of  iron  as  follows : — 

25  :  0'50  gm.  :  :  20  :  0'40  gm. 

It  must  be  remembered  that  the  solution  of  tin  is  not  permanent,  conse- 
quently it  must  be  tested  every  day  afresh.  Two  conditions  are  necessary  in 
order  to  ensure  accurate  results. 

(1)  The  iron  solution  must  be  tolerably  concentrated,  since  the  end  of 
the  reduction  by  loss  of  colour  is  more  distinct ;  and  further,  the  dilution  of 
the  liquid  to  any  extent  interferes  with  the  quantity  of  tin  solution  necessar}" 
to  effect  the  reduction.    Presenius  found  that  by  diluting  the  10  c.c.  of 
iron  solution  with  30  c.c.  of  distilled  water,  O'l  c.c.  more  was  required  than 
in  the  concentrated  state.     This  is,  however,  always  the  case  with  stannous 
chloride  in  acid  solution,  and  constitutes  the  weak  point  inStreng's  method 
of  analysis  by  its  means. 

(2)  The  addition  of  the  tin  solution  to  the  iron  must  be  so  regulated,  that 
only  a  very  small  quantity  of  iodine  is  necessary  to  estimate  the  excess ;  if 
this  is  not  done  another  source  of  error  steps  in,  namely,  the  influence  which 
dilution,  on  the  one  hand,  or  the  presence  of  great  or  small  quantities  of 
hydrochloric  acid  on  the  other,  are  known  to  exercise  over  this  reaction. 
Practically,  it  was  found  that  where  the  addition  of  tin  to  the  somewhat 
concentrated  iron  solution  was  cautiously  made,  so  that  the  colour  was  just 
discharged,  the  mixture  then  rapidly  cooled,  starch  added,  and  then  iodine 
till  it  became  blue,  the  estimation  was  extremely  accurate. 


2.     Titration   by   Sodic   Thiosulphate. 

Scherer  first  suggested  the  direct  titration  of  iron  by  thio- 
sulphate,  which  latter  was  added  to  a  solution  of  ferric  chloride 
until  no  further  violet  colour  was  produced.  This  was  found  by 
many  to  be  inexact,  but  Kremer  (Journ.  f.  Pract.  Cliem.  Ixxxiv. 
339)  has  made  a  series  of  practical  experiments,  the  result  of  which 
is  that  the  following  modified  method  can  be  recommended. 

The  reaction  which  takes  place  is  such  as  to  produce  ferrous 
chloride,  sodic  tetrathionate,  and  sodic  chloride.  2S203Na2  + 
Fe2Cl6  +  2HC1  =  S406H2  +  4JSTaCl  +  2FeCl2.  The  thiosulphate, 
which  may  conveniently  be  of  —^  strength,  is  added  in  excess, 
and  the  excess  determined  by  iodine  and  starch. 

The  Analysis :  The  iron  solution,  containing  not  more  than  1  per  cent, 
of  metal,  which  must  exist  in  the  ferric  state  without  any  excess  of  oxidizing 
material  (best  obtained  by  adding  excess  of  hydrogen  peroxide,  then  boiling 
till  the  excess  is  expelled),  is  moderately  acidified  with  hydrochloric  acid,  sodie 
acetate  added  till  the  mixture  is  red,  then  dilute  hydrochloric  acid  until  the 
red  colour  disappears ;  then  diluted  till  the  iron  amounts  to  i  or  £  per  cent., 
and  ^  thiosulphate  added  in  excess,  best  known  by  throwing  in  a  particle  of 
potassic  sulphocyanide  after  the  violet  colour  produced  has  disappeared ;  if 
any  red  colour  occurs,  more  thiosulphate  must  be  added.  Starch  and  -^r 
iodine  are  then  used  to  ascertain  the  excess.  A  mean  of  several  experi- 
ments gave  100-06  Ee,  instead  of  100. 

Oudemanns'  Method. — A  simpler  process  for  the  direct  titra- 
tion of  iron  by  thiosulphate  has  been  devised  by  Oudemanns 
(Z.  a.  C.  vi.  129  and  ix.  342),  which  gives  very  good  results. 


§  60.  IRON.  193 

The  Analysis :  To  the  dilute  ferric  solution,  which  should  not  contain 
more  than  O'l  to  0'2  gm.  Pe  in  100  c.c.  nor  much  free  HC1,  3  c.c.  of 
1  per  cent,  solution  of  cupric  sulphate  are  added,  2  c.c.  of  concentrated 
hydrochloric  acid,  and  to  about  every  100  c.c.  of  fluid,  1  c.c.  of  a  1  per  cent, 
solution  of  potassic  sulphocyanide. 

The  mixture  may  with  advantage  be  very  slightly  warmed,  and  the 
thiosulphate  delivered  in  from  the  burette  at  first  pretty  freely.  The  red 
colour  produced  by  the  sulphocyanide  gradually  fades  away ;  as  this  occurs, 
the  thiosulphate  must  be  added  in  smaller  quantities,  constantly  agitating 
the  liquid  until  it  becomes  as  colourless  as  pure  water.  If  any  doubt  exists 
as  to  the  exact  ending,  a  slight  excess  of  thiosulphate  may  be  added,  and  the 
quantity  found  by  ^V  iodine  and  starch.  Greater  accuracy  will  always  be 
insured  by  this  latter  method. 

The  accuracy  of  the  process  is  not  interfered  with  by  the 
presence  of  salts  of  the  alkalies,  strontia,  lime,  magnesia,  alumina, 
or  manganous  oxide ;  neither  do  salts  of  nickel,  cobalt,  or  copper, 
unless  their  quantity  is  such  as  to  give  colour  to  the  solution. 

The  process  is  a  rapid  one,  and  with  care  gives  very  satisfactory 
results. 

An  improvement  on  this  process  has  been  adopted  by  Haswell, 
who  mixes  the  moderately  acid  solution  of  the  ferric  chloride  in 
the  presence  of  a  cupric  salt  with  a  few  drops  of  sodic  salicylate, 
and  then  reduces  with  thiosulphate  previously  standardized  upon  a 
known  quantity  of  iron  by  the  same  method,  and  estimates  the 
excess  by  bichromate. 

The  solutions  required  are  : — 

Standard  Ferric  chloride. 
Standard  Sodic  thiosulphate. 
Standard  Potassic  bichromate,  dilute. 
Ammonio-cupric  chloride,  2  per  cent,  solution. 
Sodic  salicylate,  \  per  cent,  solution. 

The  Analysis :  10  c.c.  of  iron  solution  are  mixed  in  a  flask  with  a  few 
drops  of  HC1  and  2  c.c.  of  cupric  solution,  then  a  few  drops  of  the  salicylate : 
the  colour  should  be  pure  violet  on  dilution  with  water.  Thiosulphate  is 
then  added  until  perfectly  colourless.  The  mixture  is  then  titrated  back 
with  bichromate  till  a  faint  violet  colour  appears. 

If  —^  thiosulphate  and  bichromate  are  used,  the  calculation  is 
easy;  but  if  otherwise,  the  relative  strength  must  be  found  by 
experiment. 

Bruel  (Compt.  rend,  xcvii.  954)  modifies  this  process  by 
operating  without  the  copper  solution,  relying  merely  on  the 
discharge  of  the  violet  colour  in  a  boiling  solution  by  thiosulphate 
standardized  on  a  ferric  solution  of  known  strength. 

3.     Estimation  by   Potassic   Iodide  and  Sodic   Thiosulphate. 

When  ferric  chloride  is  digested  with  potassic  iodide  in  excess, 
iodine  is  liberated,  which  dissolves  in  the  free  potassic  iodide — 

Fed3  +  KI  =  Fed2  +  KC1  + 1. 


194  VOLUMETRIC   ANALYSIS.  §    60. 

The  Analysis :  The  hydrochloric  acid  solution,  which  must  contain  no 
free  chlorine  or  nitric  acid,  and  all  the  iron  in  the  ferric  state,  is  nearly 
neutralized  with  caustic  potash  or  soda,  transferred  to  a  well-stoppered 
flask,  and  an  excess  of  strong  solution  of  potassic  iodide  added ;  it  is  then 
heated  to  50°  or  60°  C.  on  the  water  bath,  closely  stoppered,  for  about  twenty 
minutes ;  the  flask  is  then  cooled,  starch  added,  and  titrated  with  thiosulphate 
till  the  blue  colour  disappears.  This  process  gives  very  satisfactory  results 
in  the  absence  of  all  substances  liable  to  affect  the  potassic  iodide,  such  as 
free  chlorine  or  nitric  acid,  and  is  particularly  serviceable  for  estimating 
small  quantities  of  iron. 

4.     Estimation   of   Iron  "by   Colour  Titration. 

These  methods,  which  approach  in  delicacy  the  Nessler  test 
for  ammonia,  are  applicable  for  very  minute  quantities  of  iron, 
such  as  may  occur  in  the  ash  of  bread  when  testing  for  alum,  water 
residues,  alloys,  and  similar  cases. 

It  is  first  necessary  to  have  a  standard  solution  of  iron  in  the  ferric  state, 
which  can  be  made  by  dissolving  r004  gm.  of  iron  wire  in  nitro-hydrochloric 
acid,  precipitating  with  ammonia,  washing  and  re-dissolving  the  ferric  oxide 
in  a  little  hydrochloric  acid,  then  diluting  to  1  liter.  1  c.c.  of  this  solution 
contains  1  milligram  of  pure  iron  in  the  form  of  ferric  chloride.  It  may  be 
further  diluted,  when  required,  so  as  to  contain  TV  milligram  in  a  c.c.,  and 
this  is  the  best  standard  to  use.*  The  solution  for  striking  the  colour  is 
either  potassic  ferrocyanide  or  thiocyanate  dissolved  in  water  (1  :  20) . 

Example  with  Ferrocyanide  :  The  material  containing  a  minute  unknown 
quantity  of  iron,  say  a  water  residue,  is  dissolved  in  hydrochloric  acid,  and 
diluted  to  100  c.c.,  or  any  other  convenient  measure.  10  c.c.  are  placed 
into  a  white  glass  cylinder  marked  at  100  c.c.,  1  c.c.  of  concentrated  nitric 
acid  added  (the  presence  of  free  acid  is  always  necessary  in  this  process),  then 
diluted  to  the  mark  with  distilled  water,  and  well  stirred. 

1  c.c.  of  ferrocyanide  solution  is  then  added,  well  mixed,  and  allowed  to 
stand  at  rest  a  few  minutes  to  develop  the  colour. 

A  similar  cylinder  is  then  filled  with  a  mixture  of,  say  1  c.c.  of  standard 
iron  solution,  1  c.c.  nitric  acid  and  distilled  water,  and  1  c.c.  ferrocyanide 
added;  if  this  does  not  approach  the  colour  of  the  first  mixture,  other 
quantities  of  iron  are  tried  until  an  exact  similarity  of  colour  occurs.  The 
exact  strength  of  the  iron  solution  being  known,  it  is  easy  to  arrive  at  the 
quantity  of  pure  iron  present  in  the  substance  examined,  and  to  convert  it 
into  its  state  of  combination  by  calculation.  The  colorimeter  may  of  course 
be  here  used  with  advantage. 

Carter  Bell  (J.  S.  C.  I.  viii.  175)  adopts  the  following  plan  in 
the  case  of  waters : — 70  c.c.  of  the  water  is  evaporated  to 
dryness  in  a  platinum  dish,  and  gently  ignited  to  burn  off  organic 
matters.  1  c.c.  of  dilute  nitric  acid,  50  c.c.  of  strong  acid  in 
a  liter,  is  then  poured  over  the  residue  from  a  pipette,  and 
evaporated  to  dryness  in  the  water  bath  ;  the  residue  is  then 
dissolved  in  1  c.c.  of  a  10  per  cent,  hydrochloric  acid,  5  or  10  c.c. 
of  distilled  water  added,  and  the  solution  filtered  and  washed 

*  A  solution  of  this  strength  can  also  be  made  by  weighing  07  gm.  of  pure  ammonio- 
ferrous  sulphate  (§  31.26),  dissolving  in  water,  acidifying  with  sulphuric  acid,  adding 
sufficient  permanganate  solution  to  convert  the  iron  exactly  into  ferric  salt,  then 
diluting  to  1  liter.  Hydrogen  peroxide  may  also  be  used  in  place  of  permanganate, 
taking  care  to  dissipate  the  excess  by  boiling. 


§    61.  IRON   ORES.  ]95 

through  a  small  filter,  and  made  up  to  50  c.c.  in  a  Xessler  glass ; 
and  finally  tested  with  1  c.c.  each  of  ferrocyanide  solution  and 
nitric  acid. 

With  Thiocyanate. — Thompson  (J.  C.  S.  1885,  493)  recom- 
mends this  method  as  being  specially  available  in  the  presence  of 
other  ordinary  metals  and  organic  matters,  silver,  copper,  and 
cobalt  being  the  only  interfering  substances.  The  delicacy  is  said  to 
"be  such,  that  1  part  of  iron  can  be  recognized  in  50  million  parts  of 
water.  The  presence  of  free  mineral  acids  greatly  adds  to  the 
sensitiveness.  The  standard  ferric  solution  may  be  the  same  as  for 
ferrocyanide ;  and  in  preparing  the  material  for  titration,  the 
weighed  quantity  is  dissolved  in  an  appropriate  acid,  evaporated 
nearly  to  dryness,  taken  up  with  water,  converted  into  the  ferric 
state  by  cautious  addition  of  permanganate,  then  diluted  with  water 
to  a  measured  volume,  and  an  aliquot  portion  taken  for  titration. 

The  standard  iron  used  by  Thompson  =  T1s-  m.gm.  per  c.c. 
(0*7  gm.  double  iron  salt  [oxidized]  per  liter). 

Example:  Into  two  glass  cylinders  marked  at  100  c.c.  pour  1  c.c.  of 
concentrated  nitric  or  hydrochloric  acid,  or  better,  5  c.c.  of  either  acid  of 
strength  1  :  5, 15  c.c.  of  thiocyanate,  and  to  one  glass  a  measured  volume  of  the 
solution  to  be  tested :  fill  up  both  glasses  to  the  mark.  If  iron  be  present,  a 
blood  red  colour  more  or  less  intense  will  be  produced.  Standard  iron  is  then 
cautiously  added  from  a  burette  to  the  other  glass  till  the  colour  agrees. 
The  quantity  of  Fe  taken  should  not  require  more  than  2  or  3  c.c.  of  the 
standard  to  equal  it,  or  the  colour  will  be  too  deep  for  comparison. 

If  other  metals  are  present  which  form  two  sets  of  salts,  they 
must  be  in  the  higher  state  of  oxidation,  or  the  colour  is  destroyed. 
Oxalic  acid  also  destroys  it.  Examples  in  the  presence  of  a  great 
variety  of  metals  show  very  good  results. 

IRON    ORES. 

§  61.  IN  the  analysis  of  iron  ores  it  is  very  often  necessary  to 
determine  not  only  the  total  amount  of  iron,  but  also  the  state  in 
which  it  exists ;  for  instance,  magnetic  iron  ore  consists  of  a 
mixture  of  the  two  oxides  in  tolerably  definite  proportions,  and  it 
is  sometimes  advisable  to  know  the  quantities  of  each. 

In  order  to  prevent,  therefore,  in  such  cases,  the  further  oxidation 
of  the  ferrous  oxide,  the  little  flask  apparatus  (fig.  36)  adopted  by 
Mohr  is  highly  recommended,  or  fig.  35  is  equally  serviceable. 

The  left-hand  flask  contains  the  weighed  ore  in  a  finely  powdered  state,  to 
which  tolerably  strong  hydrochloric  acid  is  added  ;  the  other  flask  contains 
distilled  water  only,  the  tube  from  the  first  flask  entering  to  the  bottom  of  the 
second.  When  the  ore  is  ready  in  the  flask  and  the  tubes  fitted,  hydrochloric 
acid  is  poured  in,  and  a  few  grains  of  sodic  bicarbonate  added  to  produce  a 
flow  of  carbonic  acid.  The  air  of  the  flask  is  thus  dispelled,  and  as  the  acid 
dissolves  the  ore,  the  gases  evolved  drive  out  in  turn  the  carbonic  acid, 
which  is  partly  absorbed  by  the  water  in  the  second  flask.  When  the  ore  is 
all  dissolved  and  the  lamp  removed,  the  water  immediately  rushes  out  of  the 

o  2 


196 


VOLUMETRIC   ANALYSIS. 


61. 


second  flask  into  the  first,  diluting  and  cooling  the  solution  of  ore,  so  that,  in 
the  majority  of  cases,  it  is  ready  for  immediate  titration.  If  not  sufficiently 
cool  or  dilute,  a  sufficient  quantity  of  boiled  and  cooled  distilled  water  is 
added. 

When  the  total  amount  of  iron  present  in  any  sample  of  ore  has 
to  be  determined,  it  is  necessary  to  reduce  any  peroxide  present  to 
the  state  of  protoxide  previous  to  titration. 


Fig.  36. 

(a)  Treatment  of  Ores  to  render  them  easily  soluble  in  Acid. — 

Hemp  el  (Berichte,  xviii.  1130)  advocates  the  roasting  of  such 
ores  as  are  naturally  difficult  of  solution  in  a  muffle  for  one  hour, 
1  part  of  ore  to  be  mixed  with  20  parts  of  calcic  and  4  parts  of 
sodic  carbonate.  By  this  means  the  formation  of  ferric  silicate  is 
avoided,  organic  matter  is  also  destroyed,  and  an  easily  soluble 
ferric  oxide  is  produced. 

(b)  Reduction  to  the  Ferrous  state. — When  permanganate  is  to 
be  used  for  titration  the  reduction  _is  always  best  made  with  zinc 
or  magnesium.     With  bichromate,  the  best  agent  is  either  pure 
sodic  sulphite,  ammonic  bisulphite,  or  stannous  chloride. 

It  is  often  difficult  to  tell  by  mere  colour  whether  the  iron  in  any 
given  solution  is  completely  reduced  to  the  ferrous  state.  In  such 
cases  it  is  well  to  spread  a  few  drops  of  solution  of  potassic  sulpho- 
cyanate  on  a  white  tile,  and  bring  a  drop  of  the  iron  solution  in 
contact  with  it.  A  distinct  red  colour  is  a  sure  indication  that 
reduction  is  not  complete  ;  a  mere  faint  tinge  is  not  an  indication, 
because  the  reaction  is  so  delicate  that  mere  exposure  to  the  air 
will  produce  an  infinitesimal  portion  of  Fe203,  sufficient  to  give 
a  faint  colour. 


§    61.  IRON   ORES.  197 

(c)  Tit  ration  of  the  Iron  Ore  Solution. — Owing  to  the  fact  that 
hydrochloric  acid  is  in  most  instances  the  only  solvent  for  some 
kinds  of  iron  ore,  technical  operators  often  prefer  bichromate  to 
permanganate  for  titration.  The  reasons  for  this  preference  are 
twofold ;  namely,  the  irregularity  which  is  liable  to  occur  in  the 
presence  of  hydrochloric  acid,  and  the  deep  colour  of  the  ferrous 
chloride.  The  first,  however,  may  be  set  aside  by  proper  pre- 
cautions, and  the  second,  by  the  use  of  lamp  or  gaslight  instead  of 
daylight.  If  the  solution  of  the  ore  is  well  diluted  and  the  liquid 
cold,  the  end  of  the  reaction  is  very  delicate ;  nevertheless,  without 
special  practice  and  judgment,  the  bichromate  method  will  be  found 
the  best  in  all  cases  where  hydrochloric  acid  has  to  be  used. 

Hart  recommends  permanganate  as  the  best  reagent  for  titration. 
He  heats  the  ore  to  redness  in  a  porcelain  tube,  for  three  hours  at 
least,  in  a  stream  of  hydrogen ;  then  cools,  and  adds  it  to  boiling 
dilute  sulphuric  acid,  at  the  same  time  passing  a  stream  of  hydrogen 
through  the  liquid,  and  titrates  with  permanganate  in  the  ordinary 
way.  Coal-gas  is  inapplicable,  as  some  of  its  constituents  absorbed 
by  the  acid  act  on  the  permanganate. 

Some  brown  haematites,  reduced  by  this  method,  yield  an  iron 
almost  insoluble  in  the  acid.  Drown  proposes  to  heat  such  ores 
in  air  or  oxygen,  to  burn  off  carbonaceous  matter  before  passing 
hydrogen  over  them ;  the  iron  then  reduced  dissolves  easily.  Most 
magnetic  ores  yield  an  insoluble  portion  containing  iron ;  for  such 
ores  this  method  is  no  better  than  ordinary  ones. 

(d)  Direct  Titration  with  Stannous  Chloride. — This  method  of 
estimating  ferric  iron  in  ores  is  extremely  expeditious ;  and  when 
the  solution  of  iron  is  strongly  acid  and  sufficiently  hot,  the  results 
are  very  concordant,  and  especially  adapted  to  the  technical 
examination  of  mining  samples. 

Drown  dissolves  iron  ore  in  hydrochloric  acid,  evaporates  nearly 
to  dryness,  adds  a  little  water,  and  then  stannous  chloride  from  a 
burette.  The  excess  of  stannous  chloride  is  estimated  by  adding 
starch  and  standard  iodine.  The  iron  solution  should  be  tolerably 
concentrated  and  warm ;  the  tin  solution  is  best  freshly  prepared  : 
1  c.c.  =  0*012  gm.  iron  =  3  c.c.  iodine  or  thereabout.  Ten  assays 
gave  a  mean  of  38*235  per  cent. ;  two  assays  with  permanganate 
gave  38 '17,  and  two  gravimetric  determinations  gave  38*14  per 
cent,  of  iron.  The  author  made  four  simultaneous  assays  in 
eighty  minutes,  the  tin  solution  being  prepared  whilst  the  ores- 
were  dissolving.  Metallic  iron  dissolved  in  hydrochloric  acid  with 
a  little  potassic  chlorate,  the  solution  being  evaporated  nearly  to 
dryness,  is  used  to  standardize  the  tin  solution. 

1.  Bed  and  Brown  Haematites. — Red  haematite  consists  generally 
of  ferric  oxide  accompanied  with  matters  insoluble  in  acids. 
Sometimes,  however,  it  contains  phosphoric  acid,  manganese,  and 
earthy  carbonates. 


198  VOLUMETRIC   ANALYSIS.  §    61. 

Brown  haematite  contains  hydrated  ferric  oxide,  often  accompanied 
by  small  quantities  of  ferrous  oxide,  manganese,  and  alumina; 
sometimes  traces  of  copper,  zinc,  nickel,  cobalt,  Avitli  lime,  magnesia, 
and  silica ;  occasionally  also  organic  matters. 

In  cases  where  the  total  iron  only  has  to  be  estimated,  it  is 
advisable  to  reduce  the  ore  to  fine  powder ;  ignite  gently  to  destroy 
organic  matters,  then  treat  with  strong  hydrochloric  acid  at  near 
boiling  heat  till  all  iron  is  dissolved,  and  in  case  ferrous  oxide 
is  present  add  small  quantities  of  potassic  chlorate,  afterwards 
evaporating  to  dryness  to  dissipate  free  chlorine ;  then  dissolve  the 
iron  with  hot  dilute  hydrochloric  acid,  filter,  and  make  up  to  a 
given  measure  for  titration. 

In  some  instances  the  insoluble  residue  persistently  retains  some 
iron  in  an  insoluble  form ;  when  this  occurs,  resort  must  be  had  to 
fluxing  the  residue  with  potassic  bisulphate,  followed  by  solution 
in  hydrochloric  acid,  or  to  Hemp  el's  method  (§61  a). 

2.  Magnetic  Iron  Ore. — The  ferrous  oxide  is  determined  first  by 
means  of  the  apparatus  fig.   35  or  36.     The  ore  is  put  into  the 
vessel  in  a  state  of  fine  powder,  strong  hydrochloric  acid  added, 
together  with  a  few  grains  of  sodic  bicarbonate,  or  still  better, 
magnesite,  and  heat  applied  gently  with  the  lamp  until  the  ore  is 
dissolved,  then  diluted  if  necessary,  and  titrated  with  "bichromate 
or  permanganate. 

Example :  0"5  gm.  of  ore  was  treated  as  above,  and  required  19'5  c.c.  of 
T^  bichromate,  which  multiplied  by  0'0056  gave  0'1092  gm.  of  iron =0' 1404 
gm.  of  ferrous  oxide =28'08  per  cent. 

The  ferric  oxide  was  now  found  by  reducing  0*5  gm.  of  the  same  ore,  and 
estimating  the  total  iron  present :  the  quantity  of  bichromate  required  was — 

59  c.c.  ^5=0-3304  gm.  total  Fe 
Deduct        0-1092  gm.  as  FeO 

Leaving  0'2212  gm.  as  Fe203 

The  result  of  the  analysis  is  therefore — 

Ferrous  oxide    ...         ...         ...  28'08  per  cent. 

Ferric  oxide       63'20 

Difference  (Gangue,  etc.)        ...       8'72        „ 

100-00 

3.  Spathose  Iron  Ore. — The  total  amount  of   ferrous  oxide  in 
this  carbonate  is  ascertained  directly  by  solution  in  hydrochloric 
acid ;  as  the  carbonic  acid  evolved  is  generally  sufficient  to  expel 
all  air,  the  tube  dipping  under  water  may  be  dispensed  with. 
Should  the  ore  be  very  impure,  zinc  may  have  to  be  added  in  order 
to  insure  the  reduction  of  all  the  iron  present. 

As  the  ore  contains,  in  most  cases,  the  carbonates  of  manganese, 
lime,  and  magnesia,  these  may  all  be  determined,  together  with  the 
iron,  as  follows  :  — 

A  weighed  portion  of  ore  is  brought  into  solution  in  hydrochloric  acid,  and 
filtered,  if  necessary,  to  separate  insoluble  silicious  matter. 


§    61.  IKON   ORES.  199 

The  solution  is  then  boiled,  with  a  few  drops  of  nitric  acid  to  peroxidize 
the  iron,  diluted,  and  sodic  carbonate  added  in  sufficient  quantity  to 
precipitate  the  ferric  oxide,  then  sodic  acetate,  and  the  whole  boiled  that  the 
precipitate  may  become  somewhat  dense  and  separate  from  the  liquid ;  filter, 
and  if  necessary,  reduce  the  oxide  of  iron  after  careful  washings,  with  zinc 
or  stannous  chloride,  and  determine  with  permanganate  or  bichromate. 

The  filtrate  containing  the  other  bases  is  treated  with  sodic  hypochlorite, 
covered,  and  set  aside  for  twenty-four  hours  in  order  to  precipitate  the 
manganese  as  hydrated  oxide,  which  is  collected  and  titrated  as  in  §  64. 

The  filtrate  from  the  last  is  mixed  with  ammonic  oxalate  to  precipitate  the 
lime,  which  is  estimated  by  permanganate,  as  in  §  48. 

The  filtrate  from  the  lime  contains  the  magnesia,  which  may  be  precipitated 
with  sodic  phosphate  and  ammonia,  and  the  precipitate  weighed  as  usual,  or 
titrated  with  uranium  solution. 

4.  Estimation  of  Iron  in  Silicates. — Wilbur  and  Whittlesey 
(C.  N.  xxii.  2)  give  a  series  of  determinations  of  iron  existing  in 
various  silicates,  either  as  mixtures  of  ferric  and  ferrous  salts  or  of 
either  separately,  which  appear  very  satisfactory. 

The  very  finely  powdered  silicate  is  mixed  with  rather  more  than  its  own 
weight  of  powdered  fluor-spar  or  cryolite  (free  from  iron)  in  a  platinum 
crucible,  covered  with  hydrochloric  acid,  and  heated  on  the  water-bath  until 
the  silicate  is  all  dissolved.  During  the  digestion  either  carbonic  acid  gas  or 
coal  gas  free  from  H2S  is  supplied  over  the  surface  of  the  liquid,  so  as  to 
prevent  access  of  air.  When  decomposition  is  complete  (the  time  varying 
with  the  nature  of  the  material),  the  mixture  is  diluted  and  titrated  with 
permanganate  in  the  usual  way  for  ferrous  oxide ;  the  ferric  oxide  can  then 
be  reduced  by  zinc  and  its  proportion  found. 

By  Hydrofluoric  Acid. — 2  gm.  of  the  finely  powdered  silicate  are  placed 
in  a  deep  platinum  crucible,  and  40  c.c.  of  hydrofluoric  acid  (containing 
about  20  per  cent.  HF)  added.  The  mixture  is  heated  to  near  the 
boiling  point  and  occasionally  stirred  with  a  platinum  wire  until  the  de- 
composition of  the  silicate  is  complete,  which  occupies  usually  about  ten 
minutes.  10  c.c.  of  pure  H'2S04  diluted  with  an  equal  quantity  of  water  are 
then  added,  and  the  heat  continued  for  a  few  minutes.  The  crucible  and  its 
contents  are  then  quickly  cooled,  diluted  with  fresh  boiled  water,  and  the 
ferrous  salt  estimated  with  permanganate  or  bichromate  as  usual. 

Leeds  (Z.  a.  C.  xvi.  323)  recommends  that  the  finely  powdered 
silicate  be  mixed  with  a  suitable  quantity  of  dilute  sulphuric 
acid,  and  air  excluded  by  CO2  during  the  action  of  the  hydrofluoric 
acid.  The  titration  may  then  at  once  be  proceeded  with  when  the 
decomposition  is  complete. 

If  the  hydrofluoric  acid  has  been  prepared  in  leaden  vessels,  it 
invariably  contains  SO2 ;  in  such  cases  it  is  necessary  to  add  to  it, 
previous  to  use,  some  concentrated  solution  of  permanganate  (avoid- 
ing excess)  so  as  to  oxidize  the  SO2. 

The  process  is  a  rapid  and  satisfactory  one,  yielding  much  more 
accurate  results  than  the  method  of  fusion  with  alkaline  carbonates 
or  acid  potassic  sulphate. 

5.  Estimation  of  Iron  in  Ores  toy  comparison  -with  the  same  weight 
of  Pure  Iron. — The  principle  of  this  method  is  fully  explained  in 


200  VOLUMETRIC  ANALYSIS.  §    61. 

§  3,  and  is,  of  course,  applicable  to  any  substance  which  can  be 
obtained  tolerably  pure,  such  as  soft  iron  wire.  The  titrating 
solution  may  be  either  permanganate  or  bichromate  of  unknown 
strength. 

6.  Colorimetric  estimation  of  Carbon  in  Steel  and  Iron. — The 
method  devised  by  Eggertz,  and  largely  adopted  by  chemists,  for 
estimation  of  combined  carbon,  is  well  known,  but  is  open  to  the 
objection  that  minute  quantities  of  carbon  cannot  be  discriminated 
by  it,  owing  to  the  colour  of  the  ferric  nitrate  present.  Stead 
((7.  -ZVL  xlvii.  285)  in  order  to  overcome  this  difficulty  has  devised  a 
method  described  as  follows  : — 

In  some  careful  investigations  on  the  nature  of  the  colouring 
matter  which  is  produced  by  the  action  of  dilute  nitric  acid  upon 
white  iron  and  steel,  it  was  found  it  had  the  property  of  being 
soluble  in  potash  and  soda  solutions,  and  that  the  alkaline  solution 
had  about  two  and  a  half  times  the  depth  of  colour  possessed  by 
the  acid  solution.  This  being  so,  it  was  clear  that  the  colouring 
matter  might  readily  be  separated  from  the  iron,  and  be  obtained 
in  an  alkaline  solution,  by  simply  adding  an  excess  of  sodic 
hydrate  to  the  nitric  acid  solution  of  iron,  and  that  the  coloured 
solution  thus  obtained  might  be  used  as  a  means  of  determining 
the  amount  of  carbon  present.  Upon  trial  this  was  found  to 
be  the  case,  and  that  as  small  a  quantity  as  O03  per  cent,  of 
carbon  could  be  readily  determined. 

The  solutions  required  are  : — 

Standard  solution  of  Mtric  acid,  1*20  sp.  gr. 

Standard  solution  of  Sodic  hydrate,  1*27  sp.  gr. 

The  Analysis :  One  gram  of  the  steel  or  iron  to  be  tested  is  weighed  off 
and  placed  in  a  200  c.c.  beaker,  and,  after  covering  with  a  watch-glass,  12  c.c. 
of  standard  nitric  acid  are  added.  The  beaker  and  contents  are  then  placed 
on  a  warm  plate,  heated  to  about  90°  to  100°  C.,  and  there  allowed  to  remain 
until  dissolved,  which  does  not  usually  take  more  than  ten  minutes.  At  the 
same  time  a  standard  iron  containing  a  known  quantity  of  carbon  is  treated 
in  exactly  the  same  way,  and  when  both  are  dissolved  30  c.c.  of  hot  water 
are  added  to  each,  and  13  c.c.  soda  solution. 

The  contents  are  now  to  be  well  shaken,  and  then  poured  into  a  glass 
measuring-jar  and  diluted  till  they  occupy  a  bulk  of  60  c.c.  After  again 
well  mixing  and  allowing  to  stand  for  ten  minutes  in  a  warm  place,  they  are 
filtered  through  dry  filters,  and  the  filtrates,  only  a  portion  of  which  is  used, 
are  compared.  This  may  be  done  by  pouring  the  two  liquids  into  two 
separate  measuring  tubes  in  such  quantity  or  proportion  that  upon  looking 
down  the  tubes  the  colours  appear  to  be  equal. 

Thus  if  50  measures  of  the  standard  solution  is  poured  into  one  tube,  and  if 
the  steel  to  be  tested  contains  say  half  as  much  as  the  standard,  there  will  be 
100  measures  of  its  colour  solution  required  to  give  the  same  tint.  The  carbon 
is  therefore  inversely  proportional  to  the  bulk  compared  with  the  standard, 
and  in  the  above  assumed  case,  if  the  standard  steel  contained  0'05  per  cent, 
carbon,  the  following  simple  equation  would  give  the  carbon  in  the  sample 
tested : — 

0-05  x  50 

— T —  =  0'025  per  cent. 


§  62.  LEAD.  201 

The  proportions  here  given  must  be  strictly  adhered  to  in  order  to  insure 
exactness.  The  colours  from  low  carbon  irons  differ  in  tint  from  those  in 
high  carbon  steels,  and  therefore  a  low  standard  specimen  must  be  used  for 
comparison. 

Stead  has  devised  a  special  colorimeter  for  the  process,  but  it  is 
evident  that  any  of  the  usual  instruments  may  be  used. 


LEAD. 

Pb  =  206-4. 

1  c.c.  ~j  permanganate    =O01032  gm.  Lead. 
1  c.c.  normal  oxalic  acid  =  0 '1032  gm.        „ 
Metallic  iron  x      1*846  =    „ 

Double  iron  salt  x      0'263  =    „ 

§  62.  THE  accurate  estimation  of  lead  is  in  most  cases  better 
effected  by  weight  than  by  measure ;  there  are,  however,  instances 
in  which  the  latter  may  be  used  with  advantage. 

1.  As  Oxalate  (Hempel).  The  acetic  lead  solution,  which  must  contain 
no  other  body  precipitable  by  oxalic  acid,  is  put  into  a  300  c.c.  flask,  and  a 
measured  quantity  of  normal  oxalic  acid  added  in  excess,  the  flask  filled  to 
the  mark  with  water,  shaken,  and  put  aside  to  settle ;  100  c.c.  of  the  clear 
liquid  may  then  be  taken,  acidified  with  sulphuric  acid,  and  titrated  with 
permanganate  for  the  excess  of  oxalic  acid.  The  amount  so  found  multiplied 
by  3,  and  deducted  from  that  originally  added,  will  give  the  quantity  combined 
with  the  lead. 

Where  the  nature  of  the  filtrate  is  such  that  permanganate  cannot  be  used 
for  titration,  the  precipitate  must  be  collected,  well  washed,  dissolved  in 
dilute  nitric  acid,  with  a  considerable  quantity  of  sodic  acetate,  sulphuric 
acid  added,  and  titrated  with  permanganate. 

In  neither  case  are  the  results  absolutely  accurate,  owing  to  the  slight 
solubility  of  the  precipitate,  but  with  careful  manipulation  the  error  need 
not  exceed  1  per  cent.  The  error  is  much  increased  in  the  presence  of 
ammoniacal  salts. 

The  technical  analysis  of  red  lead  is  best  made  as  follows  : — 

2'064  gm.  (7V  eq.  of  Pb)  are  placed  in  a  300  c.c.  porcelain  basin,  and  20  or 
30  c.c.  nitric  acid  sp.  gr.  1'2  poured  over  it,  then  warmed  gently  with  stirring. 
In  a  few  minutes  the  lead  oxide  is  dissolved  and  ;the  peroxide  left  insoluble. 
50  c.c.  of  £  oxalic  acid  are  added  and  the  mixture  boiled :  this  decomposes 
and  dissolves  the  peroxide,  leaving  uiidissolved  any  adulterant  such  as  baryta, 
lead  sulphate,  oxide  of  iron,  gypsum,  or  sand.  While  still  hot  £  permanganate 
is  added  in  moderate  portions  until  the  colour  is  permanent  for  a  few  seconds. 
The  volume  of  permanganate  deducted  from  50  gives  direct  the  percentage 
of  lead  existing  as  peroxide. 

The  total  lead  may  be  found  in  the  same  solution  by  removing  the  excess 
of  permanganate  with  a  drop  or  two  of  oxalic  acid,  neutralizing  with  ammonia, 
adding  a  good  excess  of  ammonic  or  sodic  acetate,  and  titrating  with  bichro- 
mate as  described  in  this  section. 

Lead  acetates  in  crystals  or  in  solution  may  readily  and  with 
tolerable  accuracy  be  titrated  direct  with  normal  oxalic  acid.  The 


202  VOLUMETEIC   ANALYSIS.  §    62. 

"best  effects  are  obtained  however  by  adding  the  lead  solution 
(diluted  and  rendered  clear  by  a  little  acetic  acid)  from  a  burette 
into  the  oxalic  acid  contained  in  a  flask  or  beaker,  warmed  by  a 
water-bath.  The  addition  of  the  lead  solution  is  continued  with 
shaking  and  warming  until  no  further  precipitation  takes  place. 

Another  method  for  acetates  is  to  precipitate  the  lead  with  a 
slight  excess  of  normal  sulphuric  acid  in  a  300  c.c.  flask,  fill  to  the 
mark,  estimate  the  excess  of  H2S04  in  100  c.c.  by  weight,  then 
calculate  the  combined  acid  into  lead ;  then  by  titrating  another 
portion  for  acidity  with  pheiiolphthalein,  the  proportion  of  acetic 
acid  can  be  obtained  by  deducting  the  free  H2S04  from  the  total 
acid  found. 

2.  As  Chromate  (Schwarz).  The  lead  is  precipitated  as  chromate, 
well  washed,  and  digested  with  a  weighed  excess  of  double  iron  salt  and 
hydrochloric  acid;  the  resulting  solution  contains  ferric  and  chromic  chlorides, 
together  with  lead  chloride,  and  undecomposed  iron  salt.  The  quantity  of 
the  last  is  found  by  permanganate,  and  deducted  from  the  original  weight ; 
the  remainder,  multiplied  by  the  factor  0'263,  will  give  the  weight  of  lead. 

Diehl  (Z.  a.  C.  1880,  306)  modifies  the  method  originally 
devised  by  Schwarz  by  precipitating  the  lead  with  standard 
potassic  bichromate  in  excess,  and  titrating  the  amount  of  excess 
with  sodic  thiosulphate. 

The  necessary  solutions  are — 

Standard  Potassic  bichromate  containing  7 '3 7  gm.  per  liter. 
Standard  Sodic  thiosulphate  containing  about  5  gm.  per  liter. 

The  relation  of  these  solutions  to  each  other  is  first  found 
by  blank  experiment. 

The  Analysis :  20  or  30  c.c.  of  the  bichromate  are  placed  in  a  boiling  flask, 
with  about  300  c.c.  of  water,  and  20  or  30  c.c.  of  dilute  H2S04  (1  to  2).  The 
liquid  is  then  heated  to  boiling,  and  the  thiosulphate  cautiously  dropped  in 
until  a  point  occurs  at  which  the  yellow  colour  just  disappears,  and  which 
may  be  known  by  holding  the  flask  over  white  paper  or  porcelain. 

Lead  ores  and  residues  are  treated  with  aqua  regia  and  dilute  sulphuric 
acid,  concentrated  by  evaporation  until  the  sulphuric  acid  fumes  begin  to 
appear,  then  transferred  to  a  flask  with  water,  and  boiled  in  order  to  bring 
the  ferric  sulphate,  etc.,  into  solution ;  the  solution  is  then  cooled,  and  the 
tolerably  clear  liquid  passed  through  a  thin  close  filter  previously  moistened 
with  dilute  sulphuric  acid,  and  leaving  the  bulk  of  lead  sulphate  in  the  flask. 

This  latter  is  now  boiled  with  some  strong  solution  of  neutral  ammonic 
acetate  (about  15  c.c.  for  1  gm.  of  sulphate)  and  water,  to  bring  it  into 
solution,  and  passed  through  the  same  filter,  the  filtrate  being  received  into 
a  clean  flask.  The  operation  is  repeated  with  a  smaller  quantity  of  acetate 
and  water,  and  the  filter  finally  washed  with  hot  water  containing  some 
acetate.  To  make  sure  of  dissolving  all  the  lead  out  of  the  filter,  it  is  well 
to  make  a  final  washing  with  hot  dilute  hydrochloric  acid.  The  solution  of 
lead  is  then  acidified  with  a  few  drops  of  acetic  acid,  and  precipitated  in  the 
cold  with  the  bichromate  in  moderate  excess  (not  less  than  3 — 5  c.c.),  which 
may  be  known  by  the  colour.  The  mixture  is  well  shaken,  and  set  aside  for 
half  an  hour  to  settle.  The  clear  liquid  is  then  passed  through  a  double 
filter,  the  precipitate  washed  three  or  four  times  with  cold  water,  and  the 


§  G2.  LEAD.  203 

mixed   filtrate  and  washings   titrated  with  thiosulphate   for  the   excess  of 
bichromate,  as  described  in  the  blank  experiment. 

1  c.c.  bichromate  represents  0-01032  gm.  of  lead.  The  results 
obtained  with  known  weights  of  pure  lead  salts  were  very  exact. 

Copper,  cadmium,  zinc,  ferric  salts,  and  cobalt,  do  not  interfere 
with  the  reaction,  but  all  metals  precipitable  by  chromic  acid 
should  of  course  be  removed. 

Bui ss on  again  modifies  this  method  as  follows  : — 

The  excess  of  bichromate  is  decomposed  in  the  cold  by  potassic  iodide  in 
acid  solution.  The  iodine  set  at  liberty  corresponds  exactly  with  the  amount 
of  undecomposed  bichromate. 

Preference  is  given  in  titrating  the  iodine  to  the  use  of  carbon  disulphide 
as  indicator,  since'the  yellow  colour  of  the  chromate  interferes  with  the  blue 
colour  of  starch  iodide. 

Standardizing  the  solutions. — This  will  also  show  the  method  of  analysis. 
0'25  gm.  pure  lead  is  dissolved  in  about  5  c.c.  of  hot  dilute  nitric  acid,  boiled 
to  expel  nitrous  vapours ;  the  excess  of  acid  neutralized  with  potash,  and  the 
precipitated  lead  oxide  re-dissolved  in  acetic  acid.  It  is  then  placed  in 
a  250  c.c.  flask  with  50  c.c.  of  the  bichromate  and  filled  to  the  mark,  let  stand 
fifteen  minutes,  then  a  portion  filtered  through  a  dry  filter,  and  50  c.c.= 
0*5  gm.  Pb  taken  for  titration.  It  is  acidified  moderately  with  pure 
sulphuric  acid,  a  few  crystals  of  potassic  iodide  thrown  in,  and  in  a  few 
moments  about  5  c.c.  of  carbon  disulphide,  which  assumes  a  rich  rose  colour. 
Thiosulphate  solution  is  then  run  in  from  a  burette  until  the  colour  is  just 
destroyed. 

Buisson  uses  a  standard  bichromate  containing  14*248  gm.  per  liter, 
5  c.c.  of  which  represent  O'l  gm.  lead,  but  the  same  solution  as  given  for 
Diehl'  s  process  will  suffice. 

3.  Alkalimetric  Method  (Mohr).— The  lead  is  precipitated  as  carbonate 
by   means  of  a  slight   excess   of   ammonic   carbonate,  together  with  free 
ammonia ;  the  precipitate  well  washed,  and  dissolved  in  a  measured  excess 
of   normal  nitric  acid;   neutral  solution  of   sodic  sulphate  is  then  added 
to  precipitate  the  lead  as  sulphate.    "Without  filtering,  the  excess  of  nitric 
acid  is  then  estimated  by  normal  alkali,  each  c.c.  combined  being  equal  to 
0*1032  gm.  of  lead. 

4.  As  Sulphide  (Casamajor). — The  lead,  if  not  in  a  state  convenient 
for  titration,  is  separated  as  sulphate,  well  washed,  and  while  still  moist  is 
dissolved  in  alkaline  tartrate  solution  exactly  as  in  the  case  of  copper  (see 
§  54.5) ;  the  precipitated  sulphide  separates  very  freely,  and  if  the  operation 
is  performed  in  a  white  basin  the  end-point  is  easy  of  detection. 

The  chief  drawback  to  the  method  is  the  instability  of  the  sulphide 
solution,  which  necessitates  a  fresh  standardizing  with  known  quantities  of 
metal  every  day. 

5.  Estimation  of  Lead  in  presence  of  Tin. — For  technical  purposes 
this  may  be  readily  done  as  follows  : — 

The  alloy  is  treated  with  nitric  acid,  by  which  means  the  lead  is  dissolved, 
and  the  tin  rendered  insoluble  as  stannic  acid.  The  excess  of  nitric  acid  is 
removed  by  a  very  faint  excess  of  sodic  hydrate,  then  slightly  acidified  with 
acetic  acid.  The  solution  is  diluted,  so  that  it  contains  not  less  than  half 
a  per  cent,  of  lead.  It  is  then  titrated  with  a  standard  solution  of  potassic 
ferrocyanide  containing  10'2  gm.  per  liter,  which  has  been  standardized 
against  a  lead  nitrate  solution  containing  15  987  gm.  per  liter,  using  drops 
of  ferric  chloride  solution  on  a  white  plate  as  indicator. 


204  VOLUMETRIC  ANALYSIS.  §    60. 

MAGNESIA. 

§  63.  THE  magnesia  existing  in  the  commercial  Stassfurt  salts 
used  for  manures,  etc.,  and  other  soluble  magnesia  salts,  may  very 
readily  be  determined  with  accuracy  by  Stolba's  method,  as  given 
for  P205  in  §§  23.2  and  69,  or  in  all  cases  where  separation  can  be 
made  as  ammonio-magnesic  phosphate.  The  precipitation  may  be 
hastened  considerably  by  precipitating  with  microcosmic  salt,  in 
the  presence  of  a  tolerably  large  proportion  of  ammonic  chloride, 
accompanied  with  vigorous  stirring.  Half  an  hour  quite  suffices 
to  bring  down  the  whole  of  the  double  phosphate,  and  its  adherence 
to  the  sides  of  the  beaker  is  of  no  consequence,  if  the  titration  is 
made  in  the  same  beaker,  and  with  the  same  glass  rod,  using  an 
excess  of  standard  acid,  and  titrating  back  with  weak  standard 
ammonia  and  methyl  orange. 

The  precipitate  may  also  be  titrated  with  standard  uranium 
(§  69).  Precht  (Z.  a.  C.  1379,  438)  adopts  the  following  method 
for  soluble  magnesia  salts  in  kainit,  kieserit,  etc.,  depending  upon 
the  insolubility  of  magnesic  hydrate  in  weak  caustic  potash  : — 

10  gm.  of  the  substance  are  dissolved,  filtered,  and  mixed  with 
25  c.c.  of  normal  caustic  potash,  if  it  contains  less  than  50  per 
cent,  of  magnesic  sulphate  ;  or  50  c.c.  if  it  contains  more  than 
50  per  cent.  The  mixture  is  warmed  somewhat,  transferred  to  a 
500  c.c.  flask,  and  the  volume  made  up  with  water.  After 
standing  at  rest  for  half  an  hour,  50  c.c.  of  the  clear  liquid  are 
withdrawn,  and  the  excess  of  normal  alkali  estimated  in  the  usual 
way  with  normal  acid.  Ammonium  and  metallic  salts  must  be 
absent.  l  c  c  normal  potash  =  0-02  gm.  MgO. 


ALUMINA. 

§  63A.  ALUMINA  salts  (the  alums  and  alumina  sulphate  used  in 
dyeing  and  paper-making)  may  be  titrated  for  alumina  in  the 
absence  of  iron  (except  in  mere  traces)  by  mixing  the  acid 
solutions  with  a  tolerable  quantity  of  sodic  acetate,  then  a  known 
volume  in  excess  of  T^-  phosphate  solution  (20 '9  gm.  of  ammonio- 
sodic  phosphate  per  liter),  heating  to  boiling,  without  filtration  ;  the 
excess  of  phosphate  is  found  at  once  by  titration  with  standard 
uranium.  If  iron  in  any  quantity  is  present,  it  may  be  estimated 
in  a  separate  portion  of  the  substance,  and  its  amount  deducted 
before  calculating  the  alumina.  The  latter  is  precipitated  as 
A1P04,  and  any  iron  in  like  manner  as  FePO4.  Each  c.c.  of  T^- 
phosphate  =  0*00513  gm.  A1203.  Only  available  for  rough  purposes. 

Baeyer's  Method. — As  originally  proposed,  this  process  for 
estimating  alumina  in  alums  and  aluminic  sulphates  was  carried 
out  by  two  titrations,  a  measured  portion  of  the  solution  being  first 
treated  with  an  excess  of  normal  soda  in  sufficient  quantity  to 
dissolve  the  precipitate  of  hydrate  of  alumina  first  formed.  It  was 


§    63A.  ALUMINA.  205 

then  diluted  to  a  definite  volume,  half  being  titrated  with  normal 
acid  and  litmus,  other  half  with  troposolin  00,  or  methyl  orange, 
the  difference  being  calculated  to  alumina. 

A  considerable  improvement  however  has  been  made  by  using 
phenolphthalein  as  the  indicator,  one  titration  only  being  necessary. 
The  method  is  based  on  the  fact  that,  if  to  a  solution  of  alumina, 
containing  the  indicator,  normal  soda  is  added  in  excess,  or  until 
the  red  colour  is  produced,  normal  acid  be  then  added  until  the 
colour  disappears,  the  volume  of  acid  so  required  is  less  than  the 
soda  originally  added  in  proportion  to  the  quantity  of  alumina 
present. 

The  volume  of  acid  which  so  disappears  is  in  reality  the  quantity 
necessary  to  combine  with  the  alumina  set  free  by  the  alkali ;  and 
if  this  deficient  measure  of  acid  be  multiplied  by  the  factor 
0-01716  (J-  mol.  wt.  of  A1203),  the  weight  of  alumina  will  be 
obtained.  This  factor  is  given  on  the  assumption  that  the  normal 
sulphate  A123S04  is  formed. 

The  titration  must  take  place  in  the  cold  and  in  dilute  solutions. 
Very  fair  technical  results  have  been  obtained  by  me  with  potash 
and  ammonia  alums  and  the  commercial  sulphates  of  alumina. 

Alumina  existing  as  aluminate  of  alkali  in  caustic  soda,  for 
instance,  may  be  very  well  estimated  by  taking  advantage  of  the 
fact,  that  such  alumina  is  quite  indifferent  to  methyl  orange,  but 
reacts  acid  with  phenolphthalein.  This  fact  has  been  recorded  by 
Thompson  and  others,  but  the  priority  of  discovery  appears  to  be 
due  to  Baeyer  (Z.  a.  C.  xxiv.  542),  who,  however,  used  litmus  in 
the  place  of  phenolphthalein  and  tropoeolin  00  instead  of  methyl 
orange. 

Cross  and  Bevan  (J.  S.  C.  I.  viii.  252)  in  their  examination  of 
caustic  soda  for  alumina,  found  by  experiment,  that  the  mean  of 
the  differences  between  the  titration  with  methyl  orange  and 
phenolphthalein  required  the  factor  0'0212  per  c.c.  of  normal  acid 
for  the  alumina,  pointing  to  the  salt  as  2A1203  :  5S03. 

Estimation  of  free  Acid. — Alum  cakes  or  aluminic  sulphates  of 
various  kinds  often  contain  free  H2S04,  and  many  methods  have 
been  proposed  for  its  estimation.  Baeyer  titrates  a  10  per  cent, 
solution  of  the  substance  in  water  with  normal  soda,  and  tropoeolin 
OO  or  methyl  orange. 

K.  "Williams  (C.  N.  Ivi.  194)  adopts  the  alcohol  method  by 
digesting  the  substance  for  at  least  twelve  hours  with  strong 
alcohol,  filtering  off  and  washing  with  the  same  agent,  and  titrating 
the  solution  without  dilution  or  evaporation  with  -f^  acid  and 
phenolphthalein.  The  same  authority  -also  uses  various  alkaloids, 
such  as  strychnia,  morphia,  or  quinia  to  combine  with  the  acid, 
and  thus  calculate  the  amount. 

Beilstein  and  Gross et  (Bull,  de  VAcademie  Imp.  des  Sciences 
de  St.  Petersburg  xiii.  41)  have  examined  with  great  care  all  the 


206  VOLUMETRIC   ANALYSIS.  §    64. 

proposed  methods  for  this  purpose,  and  appear  to  have  devised  one 
which  gives  very  good  technical  results. 

The  Analysis :  1  to  2  gin.  of  substance  is  dissolved  in  5  c.c.  of  water, 
5  c.c.  of  a  cold  saturated  neutral  solution  of  ammonic  sulphate  added,  and 
stirred  for  a  quarter  of  an  hour.  50  c.c.  of  95  per  cent,  alcohol  is  then 
added,  the  mixture  thrown  on  a  small  filter,  and  washed  with  50  c.c.  of  the 
same  alcohol.  The  nitrate  is  evaporated  on  the  water  bath,  the  residue  dissolved 
in  water,  and  titrated  with  -£-$  alkali  and  litmus.  The  whole  of  the  neutral 
aluminic  sulphate  is  precipitated  as  ammonia  alum,  the  alcohol  contains  all 
the  free  acid. 

MANGANESE. 

Mn  =  55,  MnO  =  71,  MnO2  =  87. 
Factors. 

Metallic  iron  x  0'63393=MnO. 

„       „  x  0-491     =Mn. 

„       „  x  0-7768  =Mn02. 

Double  iron  salt  x  0-0911   =MnO. 

Cryst.  oxalic  acid  x  0*6916  =Mn02. 

Double  iron  salt  x  0-111     =Mn02. 

1  c.c.  T^  solution  =  0-00355  gm.  MnO  or  =  0-00435  gni.  MnO2. 

§  64.  ALL  the  oxides  of  manganese,  with  the  exception  of  the 
first  or  protoxide,  when  boiled  with  hydrochloric  acid,  yield 
chlorine  in  the  following  ratios  : — 

Mn203=l  eq.  0=  2  eq.  Cl. 
Mn304=l  eq.  0=  2  eq.  Cl. 
Mn  02=1  eq.  0=  2  eq.  Cl. 
Mn  03=2  eq.  0=  4  eq.  Cl. 
Mn207=5  eq.  0=10  eq.  Cl. 

The  chlorine  so  produced  can  be  allowed  to  react  upon  a  known 
weight  of  ferrous  salt ;  and  when  the  reaction  is  completed,  the 
unchanged  amount  of  iron  salt  is  found  by  permanganate  or 
bichromate. 

Or,  the  chlorine  may  be  led  by  a  suitable  arrangement  into  a 
solution  of  potassic  iodide,  there  setting  free  an  equivalent  quantity 
of  iodine,  which  is  found  by  the  aid  of  sodic  thiosulphate. 

Or,  in  the  case  of  manganese  ores,  the  reaction  may  take  place 
with  oxalic  acid,  resulting  in  the  production  of  carbonic  acid, 
which  can  be  weighed  as  in  Fresenius'  and  Wills'  method, 
measured  as  in  Parry's  method,  or  the  amount  of  unchanged  acid 
remaining  after  the  action  can  be  found  by  permanganate.* 

*  The  literature  of  manganese  compounds  and  their  estimation  has  now  become  very 
voluminous.    The  principal  contributions  to  the  subject  are  as  follows : — 
Wright  and  Me nke  J.  C.  S.  1880,  22—48. 

Morawski  and  Stingl       Jour./,  pract.  CTiem.  xviii.  95. 
Volhard  •     Annalen,  cxcviii.  318. 

Guyard  Bull  Soc.  CTiim.  [2]  i.  88. 

Kessler  Z.  a.  C.  1879, 1-14. 

Pattinson  J.  C.  S.  1879,  365. 


§    64  MANGANESE.  207 

The  largely  increased  use  of  manganese  in  the  manufacture  of 
steel  has  now  rendered  it  imperative  that  some  rapid  and  trust- 
worthy method  of  estimation  should  be  devised,  and  happily  this 
has  been  done  simultaneously  by  two  chemists,  Pattinson  and 
Kessler;  both  have  succeeded  in  finding  a  method  of  separating 
manganese  as  dioxide,  of  perfectly  definite  composition.  Pattinson 
found  that  the  regular  precipitation  was  secured  by  ferric  chloride, 
and  Kessler  by  zinc  chloride.  Wright  and  Menke  have 
experimented  on  both  processes  with  equally  satisfactory  results, 
but  give  a  slight  preference  to  zinc.  Pattinson  titrates  the 
resulting  MnO2  with  standard  bichromate,  and  Kessler  with 
permanganate. 

Pattinson's  method  has  been  fully  described  (J.  C.  S.  1879, 
365),  and  is  essentially  as  follows : — 

1.     Precipitation   as   MnO2   and   Titration  with   Bichromate 
(Pattinson). 

The  necessary  solutions  and  reagents  are  : — 

Standard  Potassic  bichromate. — 1  c.c.  equal  to  O'Ol  gm.  Fe 
(1  dm.  =0-1  grn.  Fe). 

Standard  Ferrous  sulphate. — 10  gm.  of  iron  per  liter,  as  near 
as  may  be,  is  a  convenient  strength,  but  as  the  strength  alters  from 
time  to  time,  no  exact  quantity  need  be  taken.  53  gm.  of  ferrous 
sulphate  dissolved  in  a  mixture  of  250  c.c.  of  strong  pure  sulphuric 
acid  and  750  c.c.  of  water,  will  give  a  solution  of  about  the  pro- 
portion mentioned  (or  530  gm.  to  1000  dm.). 

Solution  of  Bleaching  powder. — This  reagent  is  used  to  oxidize 
the  manganese  before  precipitation  (Kessler  uses  bromine  water 
for  the  same  purpose).  15  gm.  per  liter,  or  150  grn.  to  1000  dm. 
The  clear  solution  is  decanted,  and  preserved  in  well-stoppered 
bottles  for  use. 

Calcic  carbonate. — Used  for  removing  the  free  acid  during 
precipitation.  It  should  be  in  tolerably  fine  powder,  and  of  granular 
texture. 

The  principle  of  the  method  is,  that  the  manganese  compound 
being  brought  into  solution  in  hydrochloric  acid,  ferric  chloride 
(if  iron  is  not  already  present)  is  added,  or  zinc  chloride  (zinc 
oxide  or  sulphate  answers  equally  well),  so  that  in  either  case 
there  is  not  less  than  the  same  quantity  of  either  of  these 
metals  present  as  there*  is  of  manganese;  an  excess  of  either 
of  them  is  of  no  consequence.  The  oxidizing  agent,  followed  by 
hot  water,  is  then  poured  into  the  mixture  so  as  to  obtain, 
a  temperature  of  about  60°  to  70°  (140° — 160°  F.),  then  a  slight 
excess  of  calcic  carbonate,  and  the  whole  well  stirred  till  all  CO2  is 
evolved,  and  the  precipitate  of  MnO2  mixed  with  iron  or  zinc,  or 


208  VOLUMETRIC   ANALYSIS.  §    64 

both,  settles  freely,  leaving  the  supernatant  liquid  clear  and  colour- 
less (in  the  case  of  using  bromine  water  the  colour  should  be 
amber,  showing  a  decided  excess  of  bromine).  In  examining 
manganiferous  irons  or  steels,  as  also  in  many  ores,  there  will 
always  be  plenty  of  iron  present;  if  this,  however,  is  not  the 
case,  it  is  always  preferable  to  use  zinc  rather  than  iron  for  the 
necessary  addition. 

Wright  and  Menke  obtained  the  best  results  when  the  solution 
was  so  diluted,  that  about  150  or  200  c.c.  of  total  fluid  (including 
the  oxidizing  solution)  were  present  for  every  0*1  gm.  MnO2  pre- 
cipitated, using  a  quantity  of  zinc  sulphate  or  ferric  chloride 
containing  from  1J  to  2  parts  of  metal  for  every  1  part  of  MnO2. 

Titration  of  the  Precipitated  MnO2. — The  precipitate  is  collected 
on  a  large  double  filter,  or  on  glass  wool,  and  washed  with  warm 
water  till  the  washings  show  no  trace  of  chlorine  or  bromine  when 
tested  with  iodized  starch-paper. 

Finally  the  precipitate,  with  its  filter,  is  returned  to  the  beaker 
in  which  it  was  originally  thrown  down,  and  which  will  contain 
traces  adhering  to  its  sides,  a  measured  excess  of  ferrous  solution 
added,  which  being  freely  acid  speedily  dissolves  the  MnO2 ;  cold 
water  is  then  added,  and  the  titration  completed  with  bichromate 
in  the  usual  way. 

As  some  filtering  paper  has  a  slight  reducing  action  upon  the 
bichromate,  it  is  well  in  standardizing  the  ferrous  solution  to  add 
about  the  same  amount  of  the  paper  as  would  be  used  in  the 
actual  analysis. 

Example  (Pattinson) :  The  standard  solution  of  ferrous  sulphate  was  of 
such  strength  that  100  dm.  =  101*1  dm.  of  bichromate.  The  100  dm.  of  iron 
solution,  after  addition  of  the  precipitated  MnO2  (from  10  grn.  of  ore), 
required  57  dm.  of  bichromate.  101*1 — 57=44*1  dm.  =  4*41  grn.  Fe;  this 
multiplied  by  the  factor  for  manganese  in  relation  to  iron  (0*491)  gave 
2*165  grn.  The  percentage  of  manganese  was  therefore  21*65. 

Should  the  ore  or  alloy  be  richer  in  manganese  than  iron,  it  is 
advisable  to  add  zinc  sulphate  or  chloride  to  make  up  the  necessary 
quantity.  The  ferrous  solution  alters  slightly  from  day  to  day, 
and  therefore  must  be  carefully  standardized  from  time  to  time. 

Kessler's  process  is  more  cumbrous  than  Pattinson' s,  and 
consists  in  reducing  the  MnO2  by  antimoriious  chloride,  then 
titrating  the  manganous  oxide  with  permanganate  standardized 
upon  manganous  pyrophosphate. 

Ores  and  Alloys  of  Manganese. — The  following  are  practical 
examples,  taken  mainly  from  Pattinson's  experience. 

Spieg-eleisen. — This  alloy  usually  contains  from  10  to  25  per  cent,  of 
manganese  and,  of  course,  a  sufficient  amount  of  iron  for  the  dioxide  pre- 
cipitation. 10  grn.  are  taken  for  analysis.  This  amount  is  dissolved  in 
about  12  dm.  of  hydrochloric  acid  with  the  aid  of  heat.  About  5  dm.  of 
nitric  acid  are  then  added  for  the  purpose  of  converting  the  ferrous  into 


§    64.  MANGANESE.  209 

ferric  chloride  (on  the  gram  system  the  quantities  would  be  1  gm.  of  alloy, 
12  c.c.  of  HC1,  and  5  c.c.  of  HNO3  respectively).  After  washing  the  cover 
and  sides  of  the  beaker  with  cold  water,  the  excess  of  acid  is  neutralized  by 
the  addition  of  calcic  carbonate  until  the  solution  has  a  reddish  colour. 
100  dm.  of  the  bleaching-powder  solution  or  about  50  dm.  of  bromine  water 
are  added,  without  previous  addition  of  hydrochloric  acid  as  in  the  case  of 
ores.  Hot  water  is  then  added  to  heat  the  solution  to  140° — 160°  F.,  and 
then  about  25  grn.  of  calcic  carbonate,  and  the  solution  well  stirred.  The 
rest  of  the  process  is  conducted  as  before  described. 

Ferro-Manganese. — For  the  quantitative  analysis  of  this  alloy  an  amount 
which  contains  from  two  to  four  grains  of  manganese  may  be  taken.  The 
solution  is  made  as  in  the  case  of  spiegeleisen.  If  the  alloy  contains  less  iron 
than  manganese,  zinc  chloride  is  added  so  as  to  make  the  amount  of  the  iron 
and  zinc  fully  equal  to  that  of  the  manganese.  The  amount  of  bleaching- 
powder  solution  to  be  added  must  depend  upon  the  amount  of  manganese  in 
solution,  taking  care  to  add  about  40  dm.  of  bleaching-powder  solution  of 
the  strength  above-named  for  every  grain  of  manganese  present. 

As  in  the  case  of  ores,  instead  of  weighing  off  separately  the  amounts 
required  for  each  test,  a  larger  quantity  may  be  dissolved  and  peroxidized, 
and,  after  making  up  the  solution  to  a  known  bulk  in  a  measuring  flask,  the 
necessary  quantities  for  the  test  measured  out. 

Steel. — 50  grn.  of  steel  are  dissolved,  by  the  aid  of  heat,  in  about  35  dm. 
of  hydrochloric  acid  of  about  1'180  sp.  gr.  The  ferrous  chloride  thus 
formed  is  then  converted  into  ferric  chloride  by  the  addition  of  about  9  dm. 
of  nitric  acid  of  about  T400  sp.  gr.  The  solution  is  made  in  a  beaker  of 
about  35-oz.  capacity.  Calcic  carbonate  is  then  added  until  the  solution  is 
slightly  red.  135  grn.  of  calcic  carbonate  are  now  weighed  or  measured 
and  about  one-half  of  this  added  to  the  solution.  After  the  effervescence  caused 
by  the  escape  of  carbonic  acid  has  ceased,  about  40  dm.  of  the  bleaching- 
powder  solution  are  added,  and  then  hot  water  to  about  150°  F.,  and  then 
the  remainder  of  the  calcic  carbonate.  If  the  latter  is  added  at  once,  the 
effervescence  is  so  great  that  the  substance  is  likely  to  froth  over  the  edges 
of  the  vessel;  and  if  the  bleaching-powder  solution  is  added  before  any 
calcic  carbonate  has  been  added,  the  chlorine  is  likely  to  be  expelled  by  the 
evolution  of  the  carbonic  acid.  The  precipitate  is  then  thrown  on  a  sufficiently 
large  filter,  and  washed  until  free  from  any  trace  of  chlorine.  Although 
the  precipitate  is  bulky  it  is  very  readily  washed. 

About  20  dm.  of  the  ferrous  sulphate  solution  are  standardized,  and  the 
same  quantity  used  for  decomposing  the  manganese  dioxide  in  the  case  of 
steels ;  but  it  is  sometimes  found  necessary  to  add  a  little  additional  sulphuric 
acid,  in  order  to  dissolve  the  ferric  oxide  precipitate  and  the  excess  of  calcic 
carbonate  it  may  contain. 

Manganese  Slags,  etc. — These  are  treated  similarly  to  the  above,  using 
for  the  analysis  such  a  quantity  as  will  not  contain  more  than  about  2*5  grn. 
of  manganese  for  the  above-named  amounts  of  reagents,  and  taking  care  to 
have  a  sufficient  amount  of  ferric  or  zinc  chloride  in  the  solution  when  the 
manganese  is  precipitated. 

Should  lead,  copper,  nickel,  or  cobalt  exist  in  the  substance  under  examin- 
ation, these  must  be  separated  before  the  manganese  is  precipitated,  as  they 
form  higher  oxides  under  the  conditions  of  the  precipitation,  which  oxides, 
like  manganese  dioxide,  convert  ferrous  into  ferric  oxide.  Fortunately,  in 
most  manganiferous  iron  ores  and  in  spiegeleisen,  ferro-manganese  and  steel, 
none  of  these  metals  occur  in  such  quantity  as  to  appreciably  affect  the 
correct  estimation  of  the  manganese. 

The  process  as  above  described  is  undoubtedly  by  far  the  best 

p 


210  VOLUMETRIC  ANALYSIS.  §    64. 

volumetric  one  known  for  the  estimation  of  manganese  in  steels 
and  ores. 

Atkinson  (/.  S.  C.  I.  v.  365)  gives  the  following  short  descrip- 
tion of  the  method  as  practically  in  daily  use  in  a  large  steel  works. 

Weigh  out  0'5  gm.  or  0'6  gm.  of  an  ore  containing  about  20  per  cent, 
manganese,  dissolve  in  7  or  8  c.c.  of  strong  HC1,  and,  when  dissolved,  wash 
the  whole,  without  filtering,  into  a  large  narrow-sided  beaker.  "When  cold 
it  is  neutralized  with  precipitated  calcic  carbonate,  until  the  liquid  assumes  a 
reddish  hue.  40  or  50  c.c.  of  saturated  bromine  water  are  added,  and  the 
mixture  allowed  to  stand  in  the  cold  for  half-an-hour.  At  the  expiration  of 
that  time  the  beaker  is  nearly  filled  up  with  boiling  water,  and  precipitated 
calcic  carbonate  added  until  there  is  no  further  effervescence,  and  part  of  the 
carbonate  is  evidently  unacted  upon.  A  small  quantity  of  spirits  of  wine  is 
then  added,  the  whole  well  stirred,  and  the  precipitate  allowed  to  settle.  The 
clear  liquid  is  filtered  off  and  fresh  boiling  water  added  to  the  residue  in  the 
beaker,  a  little  spirits  of  wine  being  used  to  reduce  any  permanganate  which 
is  formed.  The  filtration  and  washing  are  repeated  until  the  filtrate  when 
cooled  no  longer  turns  iodized  starch-paper  blue.  During  the  washing  about 
1'9  to  2*5  gm.  of  pure  granular  ferrous-ammonium  sulphate  are  weighed 
out,  washed  into  the  beaker  in  which  the  precipitation  took  place,  and  about 
30  to  50  c.c.  of  dilute  sulphuric  acid  added.  The  filter  containing  the  pre- 
cipitated MnO2  is  then  placed  in  the  beaker,  and  the  latter  is  quickly  dissolved 
by  the  oxidation  of  a  portion  of  the  ferrous  salt  into  ferric  sulphate.  The 
remaining  ferrous  iron  is  then  titrated  with  potassic  bichromate  in  the  usual 
way.  The  difference  in  the  number  of  c.c.  of  bichromate  used  from  the 
number  which  the  original  weight  of  the  ferrous-ammonium  sulphate  would 
have  required  if  directly  titrated,  is  a  measure  of  the  quantity  of  MnO2 
present.  For  rapidity  and  simplicity  this  volumetric  process  leaves  nothing 
to  be  desired ;  duplicate  experiments  agree  within  very  narrow  limits ;  and 
if  the  assumption  is  accepted  that  the  presence  of  ferric  chloride  enables  the 
complete  oxidation  of  the  manganese  to  the  state  of  peroxide,  no  other 
process  can  compete  with  it. 

Pattinson  prefers  to  use  bleach  solution  to  bromine,  because 
the  formation  of  permanganate  is  more  easily  seen.  In  any  case 
not  more  than  a  trace  of  permanganate  should  be  formed,  and  if 
the  first  experiment  shows  this  to  be  the  case,  another  trial  must 
be  commenced  with  less  oxidizing  material. 


2.     By  Precipitation  -with.   Potassic   Permanganate    (G-uyard). 

If  a  dilute  neutral  or  faintly  acid  solution  of  manganese  salt  be 
heated  to  80°  C.  and  permanganate  added,  hydrated  MnO2  is  pre- 
cipitated, and  the  end  of  the  reaction  is  known  by  the  occurrence  of 
the  usual  rose  colour  of  permanganate  in  excess.  The  reaction  is 
exact  in  neutral  solutions.  Any  large  excess  of  either  HC1  or  H2S04 
causes  irregularity,  as  also  do  ferric  or  chromic  salts;  nickel,  cobalt, 
zinc,  alumina,  or  lime,,  in  moderate  quantity  are  of  no  consequence. 

This  method  is  of  easy  execution,  and  gives  good  results  in  cases 
where  it  can  be  properly  applied,  but  such  instances  are  few. 

The  Analysis :  1  or  2  gm.  of  the  manganese  compound  are  dissolved  in 
aqua  regia,  boiled  a  few  minutes,  the  excess  of  acid  neutralized  with  alkali, 
then  diluted  largely  with  boiling  water  (1  or  2  liters),  kept  at  a  temperature 


§    64.  MANGANESE.  231 

of  80°  C.,  and  standard  permanganate  added  so  long  as  a  brownish  precipitate 
forms,  and  until  the  clear  supernatant  liquid  shows  a  distinct  rose  colour. 
2  eq.  of  permanganate =3  eq.  of  manganese,  therefore  1  c.c.  of  ^r  solution = 
0*0016542  gm.  of  Mn. 

A  modification  of  this  process  is  strongly  recommended  by 
Wright  and  Menke  (/.  C.  S.  1880,  42),  and  which  combines  the 
principle  adopted  by  Kessler  and  Pattinson;  viz.,  the  addition 
of  zinc  sulphate  to  regulate  the  precipitation  of  MiiO2. 

The  neutral  or  only  faintly  acid  solution  is  diluted,  so  that  not  more  than 
O'l  gm.  MnO2  is  contained  in  150  c.c.  A  solution  of  permanganate  is 
prepared  of  about  half-per-cent.  strength,  and  in  it  are  dissolved  crystals 
of  zinc  sulphate  in  such  proportion  that  about  ten  parts  are  present  for  every 
one  part  of  MnO2  to  be  precipitated. 

The  cold  manganese  solution  is  then  poured  into  this  mixture  slowly,  with 
gentle  shaking  or  stirring.  Of  course  there  must  be  an  excess  of  per- 
manganate which  is  shown  by  the  pink  colour.  In  a  few  minutes  the  clear 
pink  fluid  may  be  poured  off  through  a  glass  wool  filter ;  the  precipitate  of 
MnO2  (containing  some  zinc)  is  also  brought  on  the  same  filter,  washed  well 
with  cold  water,  and  finally  titrated  with  ferrous  sulphate  or  double  iron  salt, 
and  y^  permanganate  or  bichromate. 

The  numbers  obtained  by  W  r  i  gh  t  and  Menke  were  extremely  satisfactory 
with  manganese  solutions  of  known  strength. 

Volhard's  method  depends  very  much  on  the  same  principles 
as  the  foregoing,  the  details  being  as  follows  : — 

A  quantity  of  material  is  taken  so  as  to  contain  from  0'3  to  0'5  gm.  Mn, 
dissolved  in  nitric  acid,  evaporated  in  porcelain  to  dryness,  first  adding  a 
little  ammonic  nitrate,  then  heated  over  the  flame  to  destroy  organic  matter. 
The  residue  is  digested  with  HC1,  adding  a  little  strong  H2SO4,  and  again 
evaporated  to  dryness,  first  on  the  water  bath,  then  with  greater  heat  till 
vapours  of  SO3  occur.  It  is  then  washed  into  a  liter  flask  and  neutralized 
with  sodic  hydrate  or  carbonate :  sufficient  pure  zinc  oxide,  made  into  a 
cream,  is  added  to  precipitate  all  the  iron.  The  flask  is  filled  to  the  mark, 
shaken,  and  200  c.c.  filtered  off  into  a  boiling  flask,  acidified  with  2  or  3  drops 
of  nitric  acid,  heated  to  boiling,  and  titrated  with  T%-  permanganate  whilst 
still  hot. 

A  repetition  should  be  made  to  verify  the  results. 

indirect  technical  method. — This  is  in  use  at  several  works  as  a 
rapid  approximate  estimation  of  the  manganese  in  spiegels,  ferro- 
manganese,  pig-iron,  etc. 

It  consists  in  determining  the  iron  by  bichromate,  the  silicon  by 
weight,  adding  5  per  cent,  for  samples  containing  less  than  30  per 
cent.  Mn.,  or  6  per  cent,  for  richer  samples,  and  calling  the  rest 
manganese.  The  results  are  said  to  be  well  within  ±0*5  per  cent. 

The  Analysis :  0'5  gm.  of  the  sample  is  dissolved  in  dilute  H2SO4,  and 
titrated  in  the  usual  way  with  bichromate.  2  gm.  meantime  is  dissolved  in 
either  dilute  H2S04  or  HC1,  evaporated  to  dryness  on  a  hot  plate,  the  residue 
treated  again  with  acid,  the  silica  filtered  off,  ignited,  weighed,  and  calculated 
to  Si.  Then  Fe + Si  +  5  or  6  per  cent.  =  Mn. 

Experience  seems  to  show  that  the  accuracy  of  the  method  is 

p  2 


212  VOLUMETRIC   ANALYSIS.  §    64. 

greater  with  alloys  containing  only  a  moderate  proportion  of  Mil. 
(Holditch,  G.  N.  xlix.  9  ;  Atkinson,  ibid.  p.  25). 

There  are  many  other  volumetric  methods  in  use  for  estimating 
manganese  either  as  Mnoxide  or  metal,  among  which  may  be 
mentioned  that  of  Chalmers  Harvey  (G.  N.  xlvii.  2)  by  stannous 
chloride,  and  that  of  Williams  (Trans.  Amer.  Inst.  of  Mining 
Engineers,  x.  100),  which  consists  in  separating  MnO2  from  a  nitric 
solution  by  potassic  chlorate,  dissolving  in  excess  of  standard  oxalic 
acid,  and  estimating  the  excess  by  permanganate. 

A  critical  paper  on  this  process,  accompanied  with  the  results  of 
experiment,  is  contributed  by  Macintosh  (C.  N.  1.  75).  Also 
another  by  Hintz  (Z.  a.  C.  xxiv.  421 — 438)  reviewing  a  large 
number  of  volumetric  methods  for  manganese,  but  as  none  of  them 
are  more  accurate  or  convenient  than  the  methods  here  given,  they 
are  omitted; 


3.     Estimation    of   Manganese    in    small    quantities    (Chatard). 

This  method  depends  upon  the  production  of  permanganic  acid 
by  the  action  of  nitric  acid  and  lead  peroxide,  originally  used  by 
Crum  as  a  qualitative  test.  The  accuracy  of  the  process  as 
a  quantitative  one  can,  however,  only  be  depended  on  when  the 
quantity  of  manganese  is  very  small,  such  as  exists  in  some 
minerals,  soils,  etc. 

The  material  to  be  examined  is  dissolved  in  nitric  acid  and 
boiled  with  lead  peroxide,  by  which  means  any  manganese  present 
is  converted  to  permanganate ;  the  quantity  so  produced  is  then 
ascertained  by  a  weak  freshly  made  standard  solution  of  oxalic 
acid  or  ammonic  oxalate. 

The  process  gives  good  results  in  determining  manganese  in 
dolomites  and  limestones,  where  the  proportions  amount  to  from 
Tg-  to  2  per  cent.  In  larger  quantities  the  total  conversion  of  the 
manganese  cannot  be  depended  on. 

Thorpe  and  Hambly  (/.  C.  S.  liii.  182)  found  that  the  final 
point  in  the  titration  with  ammonic  oxalate  was  apt  to  be  obscured 
by  the  precipitation  of  lead  carbonate,  and  they  suggest  a 
modification  which  consists  in  using  some  dilute  sulphuric  acid 
with  the  lead  peroxide  and  nitric  acid  during  the  oxidation  of  the 
manganese  ;  no  lead  then  passes  into  solution,  and  the  filtered 
liquid  remains  perfectly  clear  on  titration.  These  operators  found 
the  method  quite  trustworthy  for  quantities  of  manganese  below 
O'Ol  gm.,  and  carried  out  as  follows  : — 

The  Analysis :  To  the  manganese  solution  which  must  be  free  from 
chlorine  and  not  too  dilute,  say  about  25  c.c.,  add  5  c.c.  of  nitric  acid 
(sp.  gr.  1'4),  2—3  gm.  of  lead  peroxide  and  10 — 20  c.c.  of  dilute  sulphuric 
acid  (1  :  2).  Boil  gently  for  about  four  minutes,  wash  down  the  sides  of 
the  flask  with  hot  water,  and  continue  the  boiling  for  half  a  minute. 
Allow  the  lead  sulphate  and  peroxide  to  subside  and  filter  at  once  (best  with 


§    64.  MANGANESE.  213 

filter  pump  through  asbestos,  previously  ignited  and  washed  with  dilute 
H2S04).  Wash  the  residue  in  flask  with  boiling  water  by  decantation,  heat 
the  clear  filtrate  to  60°  C.,  and  titrate  with  ^  ammonia  oxalate. 

Peters  avails  himself  of  this  method  for  estimating  manganese 
in  pig  iron  or  steel  by  weighing  O'l  gm.  of  the  sample,  and  boiling 
in  3  or  4  c.c.  of  nitric  acid  until  solution  of  the  metal  is  complete, 
adding  0'2  or  0*3  gm.  PbO2,  and  again  boiling  for  two  or  three 
minutes,  without  filtering  off  the  insoluble  graphite,  if  such  should 
be  present.  The  solution  is  then  cooled,  filtered  through  asbestos 
into  a  suitable  graduated  tube,  and  the  colour  compared  with  a 
standard  solution  of  permanganate  contained  in  a  similar  tube. 

The  standard  permanganate  is  best  made  by  diluting  1  c.c.  of 
T^-  solution  with  109  c.c.  of  water ;  each  c.c.  will  then  represent 
0*00001  gm.  Mn.  It  has  been  previously  mentioned  that  accurate 
results  by  this  method  can  only  be  obtained  by  using  very  small 
quantities  of  material.  Peters  finds  this  to  be  the  case,  and  hence 
recommends,  that  for  irons  containing  from  O'lO  to  0'35  per  cent, 
of  Mn  O'l  gm.  should  be  operated  upon;  when  from  0*8  to  1 
per  cent,  is  present,  O'l  gm.  of  the  sample  is  weighed  and  one- 
fourth  of  the  solution  only  treated  with  PbO2 ;  in  still  richer 
samples  proportionate  quantities  must  be  taken.  As  a  guide,  it  is 
well  to  assume,  that  when  the  amount  of  iron  taken  yields  a  colour 
equal  to  25 — 35  c.c.  of  the  standard,  the  whole  of  the  Mn  is 
oxidized.  The  actual  amount  of  manganese  in  any  test  should  not 
exceed  half  a  milligram  (C.  N.  xxxiii.  35). 

4.    Estimation  in  Spiegreleisen,   Steel,  etc.,  by  measurement  of  CO- 

(Parry). 

Parry  adopts  the  well-known  reaction  in  Fresenius  and 
Wills'  process  of  decomposing  MnO2  with  sulphuric  or  hydro- 
chloric acid  and  sodic  oxalate,  by  dissolving  a  known  weight  of 
spiegeleisen  in  strong  nitric  acid,  in  a  small  pear-shaped  flask  of 
hard  glass  ;  evaporating  to  dryness,  igniting  gently  for  ten  minutes, 
and  after  cooling  treating  the  residue  with  sodic  oxalate  and 
hydrochloric  acid,  connecting  the  flask  immediately  to  the  gas 
apparatus,  and  conveying  the  evolved  CO2  into  it  for  measurement 
over  mercury.  Parry  uses  an  apparatus  devised  by  himself,  and 
figured  in  his  paper  (C.  N.  xxix.  86);  but  any  of  the  gas 
apparatus  described  in  Part  VII.  will  suffice.  The  number  of  c.c. 
of  CO2  at  760°  m.m.  pressure  and  0°  C.  temperature  being  known, 
it  is  easy  to  calculate  the  corresponding  quantity  of  manganese. 

87  parts  by  weight  of  Mn02=88  C02=55  Manganese. 

It  was,  however,  found  impossible  to  obtain  a  product  containing 
MnO2.  Although  many  experiments  were  made  with  this  object, 
heating  over  the  Buns  en's  burner  as  previously  described,  the 
manganese  was  always  present  as  Mn203,  and  further  heating  for 


214  VOLUMETRIC  ANALYSIS.  §    64. 

thirty  minutes  showed  no  loss  of  oxygen.     Consequently,  88  parts 
of  CO2  represented  110  of  metallic  manganese. 

Example. 

0"5  gm.  of  Spiegeleisen  gave  CO2        31'80  c.c. 
Temperature       ...         ...         ...        19*00° 

Barometer  738*00  m.m. 

Tension  of  aqueous  vapour       ...         16*36  m.m 

31-8  x  721-64 

760  x  j  1  +  (0*003665  x  19)  J  ~ 
28-22  c.c.  CO2  x  0-1966  x  110 

88 
=0-06934  gm.  Mn=13"868  per  cent. 

The  calculation  may  be  simplified  by  the  use  of  the  table  at  end 
of  this  volume. 

Also  the  value  of  1  c.c.  of  CO2  shown  by  the  instrument  may  be 
expressed  in  parts  by  weight  of  Mn.  Thus,  28'22  c.c.  of  C02  = 
0-06934  gm.  of  CO2;  therefore  1  c.c.  =  0-00245716  gm.  of  Mn, 
which,  multiplied  by  x  c.c.  of  CO2  found,  gives  at  once  the 
corresponding  amount  of  manganese. 

This  method  has  been  applied  to  the  determination  of  manganese 
in  steel,  treating  not  less  than  4  gm.  of  steel,  and  measuring  over 
mercury.  The  dry  product  requires  a  rather  stronger  heat,  best 
obtained  by  heating  over  a  small  Bun  sen's  burner  in  an  open 
platinum  capsule.  It  is  best  to  take  10  gm.  of  steel  for 
solution,  evaporate  to  dryness  in  a  porcelain  dish,  and  heat  a 
weighed  portion  of  the  dry  residue  as  above,  reserving  part  for  a 
second  trial. 


5.    Technical  Examination  of  Mang-anese  Ores  used  for  Bleaching- 
Purposes,  etc. 

One  of  the  most  important  things  connected  with  the  analysis  of 
manganese  ores  is  the  determination  of  moisture.  Fresenius  has 
found  by  a  most  careful  series  of  experiments  that  the  temperature 
at  which  all  hygroscopic  moisture  is  expelled,  without  disturbing 
that  which  is  chemically  combined,  is  120°  C.,  and  this  temperature 
is  now  used  by  most  chemists.  The  drying  apparatus  devised  by 
Fresenius  consists  of  a  round  cast-iron  air  chamber,  about  ten 
inches  in  diameter,  and  two  inches  deep,  having  six  openings  at  the 
top,  into  which  little  brass  pans,  two  and  a  half  inches  in  diameter, 
are  dropped,  containing  the  very  finely  powdered  ore  ;  into  one  of 
the  pans  the  bulb  of  a  thermometer  is  placed,  imbedded  in  iron 
filings,  and  the  instrument  kept  upright  by  an  iron  rod  and  ring 
attached  to  the  upper  surface  of  the  air  chamber.  The  whole  is 
supported  by  a  tripod,  and  heated  by  a  gas  flame  to  the  required 
temperature.  The  ore,  when  powdered  and  dried  at  this  temperature, 
rapidly  absorbs  moisture  on  exposing  it  to  the  air,  and  consequently 


§    64.  MANGANESE.  215 

lias  to  be  weighed  quickly ;  it  is  better  to  keep  the  powdered  and 
dried  sample  in  a  small  light  stoppered  bottle,  the  weight  of  which, 
with  its  contents  and  stopper,  is  accurately  known.  About  1  or  2 
gm.,  or  any  other  quantity  within  a  trifle,  can  be  emptied  into 
the  proper  vessel  for  analysis,  and  the  exact  quantity  found  by 
reweighing  the  bottle. 

A  hardened  steel  or  agate  mortar  must  be  used  to  reduce  the 
mineral  to  the  finest  possible  powder,  so  as  to  insure  its  complete 
and  rapid  decomposition  by  the  hydrochloric  acid. 

Considerable  discussion  has  occurred  as  to  the  best  processes 
for  estimating  the  available  oxygen  in  manganese  ores,  arising  from 
the  fact  that  many  of  the  ores  now  occurring  in  the  market  contain 
iron  in  the  ferrous  state ;  and  if  such  ores  be  analyzed  by  the  usual 
iron  method  with  hydrochloric  acid,  a  portion  of  the  chlorine 
produced  is  employed  in  oxidizing  the  iron  contained  in  the  original 
ore.  Such  ores,  if  examined  by  Fresenius  and  Wills'  method, 
show  therefore  a  higher  percentage  than  by  the  iron  method,  since 
no  such  consumption  of  chlorine  occurs  in  the  former  process. 
Manufacturers  have  therefore  refused  to  accept  certificates  of 
analysis  of  such  ores  when  based  on  Fresenius  and  Wills' 
method.  This  renders  the  volumetric  processes  of  more  importance, 
and  hence  various  experiments  have  been  made  to  ascertain  their 
possible  sources  of  error. 

The  results  show  that  the  three  following  methods  give  very 
satisfactory  results  (see  Scherer  and  E-umpf,  C.  N.  xx.  302; 
also  Pattinson,  ibid.  xxi.  266;  and  Paul,  xxi.  16). 


6.     Direct  Analysis   by  Distillation   with  Hydrochloric   Acid. 

This  is  the  quickest  and  most  accurate  method  of  finding  the 
quantity  of  available  oxygen  present  in  any  of  the  ores  of  manganese 
or  mixtures  of  them.  It  also  possesses  the  recommendation  that  the 
quantity  of  chlorine  which  they  liberate  is  directly  expressed  in  the 
analysis  itself ;  and,  further,  gives  an  estimate  of  the  quantity  of 
hydrochloric  acid  required  for  the  decomposition  of  any  particular 
sample  of  ore,  which  is  a  matter  of  some  moment  to  the  manu- 
facturer of  bleaching  powder. 

The  apparatus  for  the  operation  may  be  those  shown  in  figs. 
29,  30,  and  34.  For  precautions  in  conducting  the  distillation 
see  §  35. 

The  Analysis :  In  order  that  the  percentage  of  dioxide  shall  be  directly 
expressed  by  the  number  of  c.c.  of  ^  thiosulphate  solution  used,  0*436  gm. 
of  the  properly  dried  and  powdered  sample  is  weighed  and  put  into  the  little 
flask;  solution  of  potassic  iodide  in  sufficient  quantity  to  absorb  all  the 
iodine  set  free  is  put  into  the  large  tube  (if  the  solution  containing  &  eq.  or 
33'2  gm.  in  the  liter  be  used,  about  70  or  80  c.c.  will  in  ordinary  cases  be 
sufficient)  ;  very  strong  hydrochloric  acid  is  then  poured  into  the  distilling 
flask,  and  the  operation  conducted  as  in  §  35.  Each  equivalent  of  iodine 
liberated  represents  1  eq.  Cl,  also  1  eq.  MnO2. 


216  VOLUMETRIC   ANALYSIS.  §    64. 

Instead  of  using  a  definite  weight,  it  is  well  to  do  as  before 
proposed,  namely,  to  pour  about  the  quantity  required  out  of  the 
weighed  sample-bottle  into  the  flask,  and  find  the  exact  weight 
afterwards. 

Barlow  (C.  N.  liii.  41)  records  a  good  method  of  separating 
Mn  from  the  metals  of  its  own  group  as  well  as  from  alkalies  and 
alkaline  earths. 

For  the  quantitative  estimation  of  Fe  and  Mil  in  the  same 
solution  as  chlorides  (other  metals  except  Cr  and  Al  may  be  present, 
but  best  absent),  solution  of  NH4C1  is  first  added,  then  strong 
NH4HO  in  excess,  boil,  then  hydrogen  peroxide  so  long  as  a 
precipitate  falls,  boil  for  a  few  minutes,  filter,  wash  with  hot  water, 
ignite,  and  weigh  the  mixed  oxides  together  as  Fe203  +  Mn304. 

The  oxides  are  then  distilled  with  HC1,  and  the  amount  of 
iodine  found  by  thiosulphate. 

The  weight  of  mixed  oxides,  minus  the  Mn304,  gives  the  weight 
of  Fe203. 

Pickering  (/.  C.  S.  1880,  128)  has  pointed  out  that  pure 
manganese  oxides,  freshly  prepared,  or  the  dry  oxides  in  very 
fine  powder,  may  be  rapidly  estimated  without  distillation  by 
merely  adding  them  to  a  large  excess  of  potassic  iodide  solution 
in  a  beaker,  running  in  2  or  3  c.c.  of  hydrochloric  acid,  when 
the  oxides  are  immediately  attacked  and  decomposed;  the  liberated 
iodine  is  then  at  once  titrated  with  thiosulphate.  Impure  oxides, 
containing  especially  ferric  oxide,  cannot  however  be  estimated  in 
this  way,  since  the  iron  would  have  the  same  effect  as  manganic 
oxide ;  hence,  distillation  must  be  resorted  to  in  the  case  of  all 
such  ores,  and  it  is  imperative  that  the  strongest  hydrochloric  acid 
should  be  used. 

Pickering's  modified  process  is  well  adapted  to  the  examination 
of  the  Weldon  mud,  for  its  available  amount  of  manganese  dioxide. 


7.     Estimation   "by   Oxalic   Acid. 

The  very  finely  powdered  ore  is  mixed  with  a  known  volume  of 
normal  oxalic  acid  solution,  sulphuric  acid  added,  and  the  mixture 
heated  and  well  shaken,  to  bring  the  materials  into  intimate  contact 
and  liberate  the  CO2.  When  the  whole  of  the  ore  is  decomposed, 
which  may  be  known  by  the  absence  of  brown  or  black  sediment, 
the  contents  of  the  vessel  are  made  up  to  a  definite  volume,  say 
300  c.c.,  and  100  c.c.  of  the  dirty  milky  fluid  well  acidified, 
diluted,  and  titrated  for  the  excess  of  oxalic  acid  by  permanganate. 
If,  in  consequence  of  the  impurities  of  the  ore,  the  mixture  be 
brown  or  reddish  coloured,  this  would  of  course  interfere  with  the 
indication  of  the  permanganate,  and  consequently  the  mixture  in 
this  case  must  be  filtered ;  the  300  c.c.  are  therefore  well  shaken 
and  poured  upon  a  large  filter.  When  about  100  c.c.  have  passed 


§    64.  MANGANESE.  217 

through,  that  quantity  can  be  taken  by  the  pipette  and  titrated  as 
in  the  former  case. 

If  the  solution  be  not  dilute  and  freely  acid,  it  will  be  found 
that  the  permanganate  produces  a  dirty  brown  colour  instead  of  its 
well-known  bright  rose-red ;  if  the  first  few  drops  of  permanganate 
produce  the  proper  colour  immediately  they  are  added,  the  solution 
is  sufficiently  acid  and  dilute. 

If  4 '3 57  gm.  of  the  ore  be  weighed  for  analysis,  the  number  of 
c.c.  of  normal  oxalic  acid  will  give  the  percentage  of  dioxide ;  but 
as  that  is  rather  a  large  quantity,  and  takes  some  time  to  dissolve 
and  decompose,  half  the  quantity  may  be  taken,  when  the  per- 
centage is  obtained  by  doubling  the  volume  of  oxalic  acid. 

Example :  The  permanganate  was  titrated  with  normal  oxalic  acid,  and  it 
was  found  that  1  c.c.=0'25  c.c.  of  normal  oxalic  acid.  2'178  gm.  of  a  rich 
sample  of  commercial  manganese  (pyrolusite)  were  treated  with  50  c.c.  of 
normal  oxalic,  together  with  5  c.c.  of  concentrated  sulphuric  acid,  until  the 
decomposition  was  complete.  The  resulting  solution  was  milky,  but  con- 
tained nothing  to  obscure  the  colour  of  the  permanganate,  and  therefore 
needed  no  nitration.  It  was  diluted  to  300  c.c.,  and  100  c.c.  taken  for  titra- 
tion,  which  required  6'2  c.c.  of  permanganate.  A  second  100  c.c.  required 
6'3,  mean  6'25,  which  multiplied  by  3  gave  18'75  c.c. ;  this  multiplied  by 
the  factor  0*25  to  convert  it  into  oxalic  acid  gave  4*68  c.c.  normal  oxalic, 
and  this  being  deducted  from  the  original  50  c.c.  used,  left  45'32  c.c.=90'64 
per  cent,  of  pure  manganic  dioxide. 

This  process  possesses  an  advantage  over  the  following,  inasmuch 
as  there  is  no  fear  of  false  results  occurring  from  the  presence  of 
air.  The  analysis  may  be  broken  off  at  any  stage,  and  resumed  at 
the  operator's  convenience. 

8.     Estimation   by  Iron. 

The  most  satisfactory  forni  of  iron  is  soft  "  flower  "  wire,  which 
is  readily  soluble  in  sulphuric  acid.  If  a  perfectly  dry  and  un- 
oxidized  double  iron  salt  be  at  hand,  its  use  saves  time.  1  mol.  of 
this  salt  =392,  representing  43 '5  of  MnO2,  consequently,  1  gm.  of 
the  latter  requires  9  gm.  of  the  double  salt ;  or  in  order  that  the 
percentage  shall  be  obtained  without  calculation,  I'lll  gm.  of  ore 
may  be  weighed  and  digested  in  the  presence  of  free  sulphuric  acid, 
with  10  gm.  of  double  iron  salt,  the  whole  of  which  would  be 
required  supposing  the  sample  were  pure  dioxide.  The  undecom- 
posed  iron  salt  remaining  at  the  end  of  the  reaction  is  estimated  by 
permanganate  or  bichromate ;  the  quantity  so  found  is  deducted 
from  the  original  10  gm.,  and  if  the  remainder  be  multiplied  by  10 
the  percentage  of  dioxide  is  gained. 

Instead  of  this  plan,  which  necessitates  exact  weighing,  any 
convenient  quantity  may  be  taken  from  the  tared  bottle,  as  before 
described,  and  digested  with  an  excess  of  double  salt,  the  weight 
of  which  is  known.  After  the  undecomposed  quantity  is  found  by 
permanganate  or  bichromate,  the  remainder  is  multiplied  by  the 


218  VOLUMETRIC  ANALYSIS.  §    64. 

factor   0*111,    which    gives    the    proportion    of    dioxide   present, 
whence  the  percentage  may  be  calculated. 

The  decomposition  of  the  ore  may  very  conveniently  be  made  in 
the  flask  apparatus  fig.  35.  The  ore  is  first  put  into  the  decom- 
posing flask,  then  the  iron  salt  and  water,  so  as  to  dissolve  the  salt 
to  some  extent  before  the  sulphuric  acid  is  added.  Sulphuric  acid 
should  be  used  in  considerable  excess,  and  the  flask  heated  by  the 
spirit  lamp  till  all  the  ore  is  decomposed;  the  solution  is  then 
cooled,  diluted,  and  the  whole  or  part  titrated  with  permanganate 
or  bichromate.  Instead  of  this  apparatus,  a  single  flask,  with  tube 
and  indiarubber  valve,  will  be  equally  convenient. 

Example :  I  gm.  of  double  iron  salt  was  titrated  with  permanganate 
solution,  of  which  21 '4  c.c.  were  required. 

rill  gm.  of  the  sample  of  manganese  was  accurately  weighed  and  digested 
with  8  gm.  of  iron  salt,  and  sulphuric  acid.  After  the  decomposition  8'8  c.c. 
of  permanganate  were  required  to  peroxidize  the  undecomposed  iron  salt 
(=0'42  gm.),  which  deducted  from  the  8  gm.  originally  used  left  7' 58  gm. ; 
or  placing  the  decimal  point  one  place  to  the  right,  75'8  per  cent,  of  pure 
dioxide. 

In  the  case  of  using  y^-  bichromate  for  the  titration,  the  following 
plan  is  convenient : — 100  c.c.  of  —$  bichromate  =  3 '92  gm.  of  double 
iron  salt  (supposing  it  to  be  perfectly  pure),  therefore  if  0'436  gm. 
of  the  sample  of  ore  be  boiled  with  3 '92  gm.  of  the  double  salt 
and  excess  of  acid,  the  number  of  c.c.  of  bichromate  required 
deducted  from  100  will  leave  the  number  corresponding  to  the 
percentage. 

Example :  0'436  gm.  of  the  same  sample  as  examined  before  was  boiled 
with  3 '92  gm.  of  double  salt,  and  afterwards  required  24  c.c.  of  ^  bichro- 
mate, which  deducted  from  100  leaves  76  per  cent,  of  dioxide,  agreeing  very 
closely  with  the  previous  examination. 

"When  using  metallic  iron  for  the  titration  (which  in  most  cases  is  preferred) 
Pattinson  proceeds  as  follows: — 30  grn.  of  clean  iron  wire  are  placed 
in  the  apparatus  fig.  35,  with  3  oz.  of  dilute  sulphuric  acid,  made  by  adding 
3  parts  of  water  to  one  of  concentrated  acid.  When  the  iron  is  quite  dissolved, 
30  grn.  of  the  finely  powdered  and  dried  sample  of  manganese  ore  to  be 
tested  are  put  into  the  flask,  the  cork  replaced,  and  the  contents  again  made 
to  boil  gently  over  a  gas  flame  until  it  is  seen  that  the  whole  of  the  black 
part  of  the  manganese  is  dissolved.  The  water  in  the  small  flask  is  then 
allowed  to  recede  through  the  bent  tube  into  the  larger  flask,  more  distilled 
water  is  added  to  rinse  out  the  small  flask  or  beaker  and  bent  tube,  the  cork 
well  rinsed,  and  the  contents  of  the  flask  made  up  to  about  8  or  10  oz.  with 
distilled  water.  The  amount  of  iron  remaining  unoxidized  in  the  solution 
is  then  ascertained  by  means  of  a  standard  solution  of  potassic  bichromate. 
The  amount  indicated  by  the  bichromate  deducted  from  the  total  amount  of 
iron  used,  gives  the  amount  of  iron  which  has  been  oxidized  by  the  manga- 
nese ore,  and  from  which  the  percentage  of  manganic  dioxide  contained  in 
the  ore  can  be  calculated.  Thus,  supposing  it  were  found  that  4  grn.  of 
iron  remained  unoxidized,  then  30 — 4—26  grn.  of  iron  which  have  been 
oxidized  by  the  30  grn.  of  ore.  Then,  as 

56  :  43-5  :  :  26  :  20'2 

the  amount  of  dioxide  in  the  30  grn.  of  ore.     The  percentage  is  therefore 
67'33.     Thus— 

30  :  20-2  :  :  100  :  67'33 


§    65.  MERCUKY.  219 

Grain  weights  are  given  in  this  example,  but  those  who  use  the 
gram  system  will  have  no  difficulty  in  arranging  the  details 
accordingly. 

The  method  generally  adopted  at  alkali  works  is  as  follows : — 

"Weigh  out  1'0875  gm.  of  the  finely  ground  dried  ore  into  a  small  flask, 
fitted  with  tube  and  elastic  valve.  Add  to  it  75  c.c.  of  a  solution  made  by 
dissolving  100  gm.  pure  ferrous  sulphate  in  water,  adding  100  c.c.  pure 
H2SO4,  and  diluting  to  a  liter.  Close  the  flask  by  its  indiarubber  stopper  con- 
taining the  valve,  and  heat  till  the  ore  is  decomposed,  leaving  only  a  light 
coloured  sediment.  After  complete  cooling,  add  about  200  c.c.  cold  water, 
and  immediately  titrate  with  ^  permanganate  to  a  faint  pink.  While  the 
ore  is  decomposing,  titrate  25  c.c.  of  the  iron  solution  to  ascertain  its  exact 
strength,  and  calculate  the  volume  for  75  c.c.  Deduct  the  difference 
between  the  two  titrations.  Each  c.c.  of  permanganate  so  found  represents 
C'02175  gm.  MnO2  or  2  per  cent. 


MERCTJRY. 

Hg=200. 

1  c.c.  ^  solution  =0-0200  gm.  Hg. 
=  0-0208  gm.  Hg20 
=  0-0271  gm.  HgCl2 

Double  iron  salt  x  0*5 104  =  Hg 

„        x  0-6914  =  HgCl* 

1.     Precipitation    as    Mercurous    Chloride. 

§  65.  THE  solution  to  be  titrated  must  not  be  warmed,  and  must 
contain  the  metal  only  in  the  form  of  protosalt.  ^  sodic  chloride 
is  added  in  slight  excess,  the  precipitate  washed  with  the  least 
possible  quantity  of  water  to  ensure  the  removal  of  all  the  sodic 
chloride ;  to  the  nitrate  a  few  drops  of  chromate  indicator  are  added, 
then  pure  sodic  carbonate  till  the  liquid  is  of  clear  yellow  colour, 
yjj-  silver  is  then  delivered  in  till  the  red  colour  occurs.  The 
quantity  of  sodic  chloride  so  found  is  deducted  from  that  originally 
used,  and  the  difference  calculated  in  the  usual  way. 

2.     By    Ferrous    Oxide    and    Permanganate    (Mohr). 

This  process  is  based  on  the  fact  that  when  mercuric  chloride 
{corrosive  sublimate)  is  brought  in  contact  with  an  alkaline  solution 
of  ferrous  oxide  in  excess,  the  latter  is  converted  into  ferric  oxide, 
while  the  mercury  is  reduced  to  mercurous  chloride  (calomel).  The 
excess  of  ferrous  oxide  is  then  found  by  permanganate  or  bichro- 
mate— 

2HgCl2  +  2FeCl2  =  Hg2Cl2  +  Fe2Cl6. 

It  is  therefore  advisable  in  all  cases  to  convert  the  mercury  to  be 
estimated  into  the  form  of  sublimate,  by  evaporating  it  to  dryness 
with  nitre-hydrochloric  acid ;  this  must  take  place,  however,  below 


220  VOLUMETRIC   ANALYSIS.  §    65. 

boiling  heat,  as  vapours  of  chloride  escape  with  steam  at  100°  C. 
(Fresenius). 

Mtric  acid  or  free  chlorine  must  be  altogether  absent  during  the 
decomposition  with  the  iron  protosalt,  otherwise  the  residual 
titration  will  be  inexact,  and  the  quantity  of  the  iron  salt  must  be 
more  than  sufficient  to  absorb  half  the  chlorine  in  the  sublimate. 

Example :  1  gm.  of  pure  sublimate  was  dissolved  in  warm  water,  and 
3  gm.  of  double  iron  salt  added,  then  solution  of  caustic  soda  till  freely 
alkaline.  The  mixture  became  muddy  and  dark  in  colour,  and  was  well 
shaken  for  a  few  minutes,  then  sodic  chloride  and  sulphuric  acid  added,  con- 
tinuing the  shaking  till  the  colour  disappeared  and  the  precipitate  of  ferric 
oxide  dissolved,  leaving  the  calomel  white ;  it  was  then  diluted  to  300  c.c. 
filtered  through  a  dry  filter,  and  100  c.c.  titrated  with  &  permanganate,  of 
which  13'2  c.c.  were  required — 13'2x3— 39'6,  which  deducted  from  76'5  c.c., 
(the  quantity  required  for  3  gm.  double  iron  salt)  left  36'9  c.c.=l'447  gm. 
of  undecomposed  iron  salt,  which  multiplied  by  the  factor  0'6914,  gave 
T0005  gm.  of  sublimate,  instead  of  1  gm.,  or  the  36'9  c.c.  may  be  multiplied 
by  the  ^  factor  for  mercuric  chloride,  which  will  give  1  gm.  exactly. 

3.      By    Iodine    and    Thiosulphate    (Hem pel). 

If  the  mercury  exist  as  a  protosalt  it  is  precipitated  by  sodic 
chloride,  the  precipitate  well  washed  and  together  with  its  filter 
pushed  through  the  funnel  into  a  stoppered  flask,  a  sufficient 
quantity  of  potassic  iodide  added,  together  with  -—  iodine  solution 
(to  1  gm.  of  calomel  about  2 '5  gm.  of  iodide,  and  100  c.c.  of  T^- 
iodine),  the  flask  closed,  and  shaken  till  the  precipitate  has 
dissolved — 

Hg2Cl2  +  6KI  +  21  =  2HgK2rt  +  2KCL 

The  brown  solution  is  then  titrated  with  ~  thiosulphate  till 
colourless,  diluted  to  a  definite  volume,  and  a  measured  portion 
titrated  with  T^-  iodine  and  starch  for  the  excess  of  thiosulphate. 
1  c.c.  YQ-  iodine  =  0'02  gm.  Hg. 

Where  the  mercurial  solution  contains  nitric  acid,  or  the  metal 
exists  as  peroxide,  it  may  be  converted  into  protochloride  by  the 
reducing  action  of  ferrous  sulphate,  as  in  Mohr's  method.  The 
solution  must  contain  hydrochloric  acid  or  common  salt  in  sufficient 
quantity  to  transform  all  the  mercury  into  calomel.  At  least  three 
times  the  weight  of  mercury  present  of  ferrous  sulphate  in  solution 
is  to  be  added,  then  caustic  soda  in  excess,  the  muddy  liquid  well 
shaken  for  a  few  minutes,  then  dilute  sulphuric  acid  added  in 
excess,  and  the  mixture  stirred  till  the  dark-coloured  precipitate 
has  become  perfectly  white.  The  calomel  so  obtained  is  collected 
on  a  filter,  well  washed,  and  titrated  with  y^  iodine  and  thiosulphate 
as  above. 

4.      Direct    Titration    with    Sodic    Thiosulphate    (Scherer).' 

The  standard  thiosulphate  is  made  by  dissolving  ^  eq.  =  12'4 
gm.  of  the  salt  in  1  liter  of  water. 


§    65.  MEKCURY.  221 

The  reaction  which  takes  place  with  thiosulphate  in  the  ca&e  of 
mercurous  nitrate  is 


Hg2(X03)2  +  Na2S203  =  Hg2S  +  ]STa2S04  +  ^T205. 
With  mercuric  nitrate  — 

3Hg(N03)2  +  2ATa2S203  =  2HgS.Hg(]ST03)2  +  2N 
With  mercuric  chloride  — 

3HgCl2  +  2Na2S203  +  2H20=2HgS.HgCl2  +  2ffa2S04  +  4HC1. 

(a)  Mercurous  Salts.  —  The  solution  containing  the  metal  as  a  proto- 
salt  only  is  diluted,  gently  heated,  and  the  thiosulphate  delivered  in  from  the 
burette  at  intervals,  meanwhile  well  shaking  until  the  last  drop  produces  no 
brown  colour.  The  sulphide  settles  freely,  and  allows  the  end  of  the  reaction 
to  be  easily  seen.  1  c.c.  of  thiosulphate=0-020  gm.  Hg.,  or  0'0208  gm. 


(b)  Mercuric  Nitrate.  —  The  solution  is  considerably  diluted,  put  into  a 
stoppered  flask,  nitric  acid  added,  and  the  thiosulphate  cautiously  delivered 
from  the  burette,  vigorously  shaken  meanwhile,  until  the  last  drop  produces 
no  further  yellow  precipitate.     Scherer  recommends  that  when  the  greater 
part  of  the  metal  is  precipitated,  the  mixture  should  be  diluted  to  a  definite 
volume,  the  precipitate  allowed  to  settle,  and  a  measured  quantity  of  the 
clear  liquid  taken  for  titration  ;  the  analysis  may  then  be  checked  by  a  second 
titration  of  the  clear  liquid,  if  needful.     1  c.c.  thiosulphate=0'015  gm.  Hg., 
or  0-0162  gm.  HgO. 

(c)  Mercuric  Chloride.  —  With  mercuric  chloride  (sublimate)  the  end  of 
the  process  is  not  so  easily  seen.    The  procedure  is  as  follows  :  —  The  very 
dilute  solution  is  acidified  with  hydrochloric  acid,  heated  nearly  to  boiling, 
and  the  thiosulphate  cautiously  added  so  long  as  a  white  precipitate  is  seen 
to  form  ;  any  great  excess  of  the  precipitant  produces  a  dirty-looking  colour. 
Piltration  is  necessary  to  distinguish  the  exact  ending  of  the  reaction,  for 
which  purpose  Beale's  filter  (fig.  19)  is  useful. 

Liebig's  method  is  the  reverse  of  that  used  for  determining 
chlorides  in  urine,  sodic  phosphate  being  used  as  indicator  in  the 
estimation  of  mercury,  instead  of  the  urea  occurring  naturally  in 
urine.  The  method  is  capable  of  very  slight  application. 


5.     As    Mercuric    Iodide    (Personne),    Compt.    Rend.    Ivi.    63. 

This  process  is  founded  on  the  fact  that  if  a  solution  of  mercuric 
chloride  be  added  to  one  of  potassic  iodide,  in  the  proportion  of 
1  equivalent  of  the  former  to  4  of  the  latter,  red  mercuric  iodide  is 
formed,  which  dissolves  to  a  colourless  solution  until  the  balance  is 
overstepped,  when  the  brilliant  red  colour  of  the  iodide  appears  as 
a  precipitate,  which,  even  in  the  smallest  quantity,  communicates 
its  tint  to  the  liquid.  The  mercuric  solution  must  always  be  added 
to  the  potassic  iodide ;  a  reversal  of  the  process,  though  giving 
eventually  the  same  quantitative  reaction,  is  nevertheless  much  less 
speedy  and  trustworthy.  The  mercurial  compounds  to  be  estimated 


222  VOLUMETRIC   ANALYSIS.  §    65. 

by  this  process  must  invariably  be  brought  into  the  form  of  neutral 
mercuric  chloride. 

The  standard  solutions  required  are  decinormal,  made  as  follows : — 

Solution  of  Potassic  iodide. — 33 -2  gm.  of  pure  salt  to  1  liter. 
1  c.c.=0-01  gm.  Hg,  or  0-01355  gm.  HgCl2. 

Solution  of  Mercuric  chloride. — 13 '537  gm.  of  the  salt,  with 
about  30  gm.  of  pure  sodic  chloride  (to  assist  solution),  are  dissolved 
to  1  liter.  1  c.c.  =0-1  gm.  Hg. 

The  conversion  of  various  forms  of  mercury  into  mercuric  chloride 
is,  according  to  Personne,  best  effected  by  heating  with  caustic 
soda  or  potash,  and  passing  chlorine  gas  into  the  mixture,  which 
is  afterwards  boiled  to  expel  excess  of  chlorine  (the  mercuric 
chloride  is  not  volatile  at  boiling  temperature  when  associated  with 
alkaline  chloride).  The  solution  is  then  coole'd  and  diluted  to  a 
given  volume,  placed  in  a  burette,  and  delivered  into  a  measured 
volume  of  the  decinormal  potassic  iodide  until  the  characteristic 
colour  occurs.  It  is  preferable  to  dilute  the  mercuric  solution  con- 
siderably, and  make  up  to  a  given  measure,  say  300  or  500  c.c. ; 
and  as  a  preliminary  trial  take  20  c.c.  or  so  of  iodide  solution, 
and  titrate  it  with  the  mercuric  solution  approximately  with  a 
graduated  pipette ;  the  exact  strength  may  then  be  found  by  using 
a  burette  of  sufficient  size. 


6.     By    Potassic    Cyanide    (Hannay). 

This  process  is  exceedingly  valuable  for  the  estimation  of  almost 
all  the  salts  of  mercury  when  they  occur,  or  can  be  separated,  in  a 
tolerably  pure  state.  Organic  compounds  are  of  no  consequence 
unless  they  affect  the  colour  of  the  solution. 

The  method  depends  on  the  fact  that  free  ammonia  produces  a 
precipitate,  or  (when  the  quantity  of  mercury  is  very  small)  an 
opalescence  in  mercurial  solutions,  which  is  removed  by  a  definite 
amount  of  potassic  cyanide.  The  operation  is  performed  in  a  flask 
or  beaker  standing  upon  a  dull  black  ground,  such  as  unglazed 
black  paper  or  black  velvet. 

The  delicacy  of  the  reaction  is  interfered  with  by  excessive 
quantities  of  ammoniacal  salts,  or  by  caustic  soda  or  potash ;  but 
this  difficulty  is  set  aside  by  the  modification  suggested  by  Tusoii 
and  Neison(/.  C.  S.  1877,  679). 

Mercury  compounds,  insoluble  in  water,  must  be  dissolved  in 
nitric,  sulphuric,  or  hydrochloric  acid,  or  in  some  cases  it  may  be 
necessary  <tto  use  aqua  regia.  The  solution  so  obtained  is  then 
mixed  with  a  certain  proportion  of  ammonic  chloride  and  potassic 
carbonate,  when  the  characteristic  precipitate  is  at  once  formed, 
and  may  be  removed  by  standard  cyanide. 


§  66.  NICKEL.  223 

The  standard  solutions  are  : — 

Decinormal  Mercuric  chloride. — 13 '537  gm.  per  liter. 

Solution  of  Potassic  cyanide  of  corresponding  strength,  made  by 
dissolving  about  17  gm.  of  pure  crystals  of  potassic  cyanide  in  a 
liter  of  water. 

It  is  also  desirable  to  have — 

Solution  of  Ammonic  chloride. — 5*36  gm.  per  liter. 

Solution  of  Potassic  carbonate. — 69  gm.  per  liter. 

Ammonic  hydrate. — One  part  of  strong  solution  to  nine  parts 
of  water. 

These  latter  solutions  are  used  according  to  the  judgment  of  the 
operator  as  may  be  necessary,  bearing  in  mind  that  in  no  case 
should  there  be  present  during  titration  an  amount  of  ammoniacal 
salt  more  than  ten  or  fifteen  times  that  of  the  mercury  to  be 
estimated.  It  is  best  to  have  the  conditions  as  nearly  as  possible 
the  same  in  any  given  analysis  as  existed  in  the  original  titration 
of  the  standard  solutions. 

Where  the  mercury  compound  is  only  slightly  acid,  the  free 
ammonia  may  be  used  for  neutralizing ;  on  the  other  hand,  in  the 
case  of  much  free  acid,  potassic  carbonate  should  be  used  for  this 
purpose,  preceded  by  some  ammonic  chloride  in  moderate  quantity 
to  produce  the  precipitate.  If  any  mercurial  solution  should  be 
largely  contaminated  with  ammonia  compounds,  potassic  carbonate 
is  added  in  excess,  and  the  mixture  boiled  to  remove  the  ammonia. 
No  mercury  is  lost  by  this  method,  but  on  the-  other  hand  it  is 
unsafe  to  attempt  the  removal  of  free  acid  by  boiling,  as  mercury 
is  easily  lost  under  such  conditions. 

Titration  of  the  Potassic  Cyanide:  50  c.c.  of  the  standard  mercuric 
chloride  being  measured  into  a  beaker  standing  on  a  black  surface,  there  are 
added  to  it  2  or  3  c.c.  of  ammonic  chloride  and  a  drop  or  two  of  ammonia. 
The  cyanide  is  then  run  cautiously  in  from  the  burette  with  constant  stirring, 
until  the  last  trace  of  opalescence  disappears.  If  the  volume  of  cyanide  is 
less  than  50  c.c.  it  may  be  diluted  to  the  requisite  strength,  or  if  more,  a  factor 
found  for  calculation.  The  solution  varies  slightly  from  time  to  time,  and 
hence  must  be  verified  before  used. 

Tuson  found  the  process  exceedingly  accurate  in  a  long  series  of 
experiments  upon  various  salts  of  mercury.  In  the  case  of  very 
small  quantities  of  the  metal  T£o-  cyanide  should  be  used. 

NICKEL. 

§  66.  THE  estimation  of  this  metal  volumetrically  has  not 
hitherto  been  very  satisfactory.  If  a  solution  of  it  in  a  tolerably 
pure  state  can  be  obtained  by  the  removal  of  other  metals  and 


224  VOLUMETRIC  ANALYSIS.  §    67. 

substances  liable  to  interfere  with  its  precipitation  as  oxalate,  it 
may  be  titrated  in  that  form  in  the  same  way  as  zinc  (§  78).  The 
estimation  in  conjunction  with  cobalt  is  given  in  §  53. 

Moore  (C.  N.  lix.  160,  293)  has  described  a  process  which  gives 
rapid  and  fairly  good  technical  results,  comparing  favourably  with 
electro  estimations. 

The  method  is  based  on  the  formation  of  a  double  cyanide  of 
nickel  and  potassium,  in  alkaline  solution,  with  cupric  ferrocyanide 
as  indicator. 

The  solutions  required  are — 

Pure  Potassic  cyanide,  22  to  25  gm.  per  liter,  so  that  20  c.c. 
shall  about  equal  O'l  gm.  Xi.  This  should  be  standardized  on 
pure  metal. 

Cupric  ferrocyanide  indicator,  prepared  by  precipitating  a  weak 
solution  of  cupric  sulphate  with  potassic  ferrocyanide,  and  dis- 
solving the  precipitate  after  decantation  in  a  solution  of  ammonic 
oxalate. 

The  Analysis  :  To  the  slightly  acid  solution  of  the  metal  (which  may  also 
contain  Fe,  Zn,  Al  or  Mn,  the  latter  in  small  quantity,  also  sulphates,  nitrates, 
chlorides,  or  acetates,  but  not  very  large  quantities  of  free  ammonia)  in  a 
white  porcelain  basin,  an  excess  of  sodic  pyrophosphate  is  added,  until  the 
precipitate  first  formed  is  dissolved ;  the  liquid  is  then  made  faintly  acid  with 
HC1,  and  finally  distinctly  alkaline  with  NH3.  The  standard  cyanide  is  then 
run  in,  with  constant  stirring,  until  the  blue  colour  disappears,  and  gives 
place  to  a  yellowish  tint.  A  measured  quantity  of  the  indicator  is  now 
added,  which  imparts  its  own  violet-brown  colour;  the  addition  of  the  cyanide 
is  cautiously  continued  until  the  colour  is  destroyed.  Practice  is  necessary 
to  distinguish  the  proper  end-reaction.  When  zinc  is  present  the  cyanide 
must  be  added  slowly,  and  only  until  the  ferrocyanide  colour  vanishes,  as 
if  continued  until  the  yellow  colour  occurs,  the  results  will  be  too  high. 


NITROGEN    AS    NITRATES    AND    NITRITES. 
Nitric    Anhydride. 

N205=108. 

Nitrous   Anhydride. 

-  76. 


Factors. 

Normal  acid  x  0-0540  =  N205 

Ditto  x  0-101  1=K]ST03 

Metallic  iron  x  0-3750  =  HM)3 

Ditto  x  0-6018  = 

Ditto  x  0-3214  = 


§  67.  THE  accurate  estimation  of  nitric  acid  in  combination 
presents  great  difficulties,  and  can  only  be  secured  by  indirect 
means;  the  methods  here  given  are  sufficient  for  most  purposes. 


§  67.  NITUA.TES.  225 

Very  few  of  them  can  be  said  to  be  simple,  but  it  is  to  be  feared 
that  no  simple  process  can  ever  be  obtained  for  the  determination 
of  nitric  acid  in  many  of  its  combinations. 

1.     Gay   Lussac's   Method  modified   by  Abel   (applicable  only 
to   Alkaline   Nitrates). 

This  process  depends  upon  the  conversion  of  potassic  or  sodic 
nitrates  into  carbonates  by  ignition  with  carbon,  and  the  titration 
of  the  carbonate  so  obtained  by  normal  acid.  The  number  of  c.c. 
of  normal  acid  required  multiplied  by  0*101  will  give  the  weight 
of  pure  potassic  nitrates  in  grams;  by  0*085,  the  weight  of  sodic 
nitrate  in  grams. 

The  best  method  of  procedure  is  as  follows  : — 

The  sample  is  finely  powdered  and  dried  in  an  air  bath,  and  1  gm.,  or  an 
equivalent  quantity  in  grains,  weighed,  introduced  into  a  platinum  crucible, 
and  mixed  with  a  fourth  of  its  weight  of  pure  graphite  (prepared  by 
Brodie's  process),  and  four  times  its  weight  of  pure  ignited  sodic  chloride. 
The  crucible  is  then  covered  and  heated  moderately  for  twenty  minutes  over 
aBunsen's  burner,  or  for  eight  or  ten  minutes  in  a  muffle  (the  heat  must 
not  be  so  great  as  to  volatilize  the  chloride  of  sodium  to  any  extent).  If 
sulphates  are  present  they  will  be  reduced  to  sulphides ;  and  as  these  would 
consume  the  normal  acid,  and  so  lead  to  false  results,  it  is  necessary  to 
sprinkle  the  fused  mass  with  a  little  powdered  potassic  chlorate,  and  heat 
again  moderately  till  all  effervescence  has  ceased.  The  crucible  is  then  set 
aside  to  cool,  warm  water  added,  the  contents  brought  upon  a  filter,  and 
washed  with  hot  water  till  the  washings  are  no  longer  alkaline.  The  filtrate 
is  then  titrated  with  normal  acid  in  the  ordinary  way. 

2.      Estimation   of   Nitrates   by   Distillation   with   Sulphuric   Acid. 

This  method  is  of  very  general  application,  but  particularly  so 
with  the  impure  alkaline  nitrates  of  commerce.  The  process  needs 
careful  manipulation,  but  yields  accurate  results. 

There  are  two  methods  of  procedure. 

(a)  To  bring  the  weighed  nitrate  into  a  small  tubulated  retort  with  a 
cooled  mixture  of  water  and  strong  sulphuric  acid,  in  the  proportion  of  10  c.c. 
of  water  and  5  c.c.  of  sulphuric  acid  for  1  gm.  of  nitrate.     The  neck  of  the 
retort  is  drawn  out  to  a  point  and  bent  downward,  entering  a  potash  or  other 
convenient  bulb  apparatus  containing  normal  caustic  alkali.     The  retort  is 
then  buried  to  its  neck  in  the  sand-bath,  and  heated  to  170°  C.  (338°  Fahr.) 
so  long  as  any  liquid  distils  over;   the  heat  must  never  exceed  175°  C. 
(347°  Fahr.),  otherwise  traces  of   sulphuric  acid  will  come  over  with  the 
nitric  acid.     The  quantity  of  acid  distilled  over  is  found  by  titrating  the 
fluid  in  the  receiver  with  normal  acid  as  usual. 

(b)  Distillation  in  a  Partial  Vacuum    (Finkener). — By    this 
arrangement  there  is  no  danger  of  contaminating  the  distillate  with 
sulphuric  acid,  inasmuch  as  the  operation  is  conducted  in  a  water 
bath,  and  when  once  set  going  needs  no  superintendence. 

The  retort  is  the  same  as  before  described,  but  the  neck  is  not  drawn  out 
or  bent ;  the  stopper  of  the  tubulure  must  be  well  ground.  The  receiver  is 

Q 


226 


VOLUMETRIC   ANALYSIS. 


§   67 


a  200-c.c.  flask  with  narrow  neck,  containing  the  requisite  quantity  of  normal 
alkali  diluted  to  about  30  c.c.  The  receiver  is  bound,  air-tight,  to  the  neck 
of  the  retort  (which  should  reach  nearly  to  the  middle  of  the  flask)  by 
means  of  a  vulcanized  tube :  the  proportions  of  acid  and  water  before  men- 
tioned are  introduced  into  the  retort  with  a  tube  funnel.  The  stopper  of  the 
retort  is  then  removed,  and  the  contents,  both  of  the  receiver  and  retort, 
heated  by  spirit  or  gas  lamp  to  boiling,  so  as  to  drive  out  the  air;  the 
weighed  nitrate  contained  in  a  small  tube  is  then  dropped  into  the  retort, 
the  stopper  inserted,  the  lamps  removed,  and  the  retort  brought  into  the 
water  bath,  while  the  receiver  is  kept  cool  with  wet  tow,  or  placed  in  cold 
water.  The  distillate  is  titrated  as  before.  1  or  2  gm.  of  saltpetre  require 
about  four  hours  for  the  completion  of  the  process. 

Finkener  obtained  very  accurate  results  by  this  method. 
When  chlorides  are  present  in  the  nitrate,  a  small  quantity  of 
moist  oxide  of  silver  is  added  to  the  mixture  before  distillation. 


3. 


Estimation   by   conversion   into   Ammonia    (Schulze   and 
Vernon   Harcourt). 


The  principle  of  this  method  is  based  on  the  fact  that  when  a 
nitrate  is  heated  with  a  strong  alkaline  solution,  and  zinc  added, 


Pig.  37. 

ammonia  is  evolved;  when  zinc  alone  is  used,  however,  the  quantity 
of  ammonia  liberated  is  not  a  constant  measure  of  the  nitric  acid 
present.  Vernon  Harcourt  and  Siewert  appear  to  have 
arrived  independently  at  the  result  that  by  using  a  mixture  of  zinc 
and  iron  the  reaction  was  perfect  (/.  C.  S.  1862,  381 ;  An.  Cliem. 
u.  Phar.  cxxv.  293). 

A  convenient  form  of  apparatus  is  shown  in  fig.  37. 

The  distilling  flask  holds  about  200  c.c.,  and  is  closely  connected  by  a  bent 
tube  with  another  smaller  flask,  in  such  a  manner  that  both  may  be  placed 
obliquely  upon  a  sand-bath,  the  bulb  of  the  smaller  flask  coming  just  under 
the  neck  of  the  larger.  The  oblique  direction  prevents  the  spirting  of  the 
boiling  liquids  from  entering  the  exit  tubes,  but  as  a  further  precaution, 


§  67.  NITRATES.  227 

these  latter  are  in  both  flasks  turned  into  the  form  of  a  hook;  from  the  second 
flask,  which  must  be  somewhat  wide  in  the  mouth,  a  long  tube  passes  through 
a  Liebig's  condenser  (which  may  be  made  of  wide  glass  tube)  into  an 
ordinary  tubulated  receiver,  containing  normal  sulphuric  acid  coloured  with 
an  indicator.  The  end  of  the  distilling  tube  reaches  to  about  the  middle  of 
the  receiver,  through  the  tubulure  of  which  Harcourt  passes  a  bulb 
apparatus  of  peculiar  form,  containing  also  coloured  normal  acid  ;  instead  of 
this  latter,  however,  a  chloride  of  calcium  tube,  filled  with  broken  glass,  and 
moistened  with  acid,  will  answer  the  purpose.  The  distilling  tube  should  be 
cut  at  about  two  inches  from  the  cork  of  the  second  flask,  and  connected  by 
means  of  a  well-fitting  vulcanized  tube ;  by  this  means  water  may  be  passed 
through  the  tube  when  the  distillation  is  over  so  as  to  remove  any  traces  of 
ammonia  which  may  be  retained  on  its  sides.  All  the  corks  of  the  apparatus 
should  be  soaked  in  hot  paraffine,  so  as  to  fill  up  the  pores. 

All  being  ready,  about  50  gm.  of  finely  granulated  zinc  (best  made  by 
pouring  molten  zinc  into  a  warm  iron  mortar  while  the  pestle  is  rapidly  being 
rubbed  round)  are  put  into  the  larger  flask  with  about  half  the  quantity  of 
clean  iron  filings  which  have  been  ignited  in  a  covered  crucible  (fresh  iron 
and  zinc  should  be  used  for  each  analysis)  ;  the  weighed  nitrate  is  then 
introduced,  either  in  solution,  or  with  water  in  sufficient  quantity  to 
dissolve  it,  strong  solution  of  caustic  potash  added,  and  the  flask  immediately 
connected  with  the  apparatus,  and  placed  on  a  small  sand-bath,  which  can 
be  heated  by  a  gas-burner,  a  little  water  being  previously  put  into  the 
second  flask.  Convenient  proportions  of  material  are  |  gm.  nitre,  and 
about  25  c.c.  each  of  water,  and  solution  of  potash  of  spec.  grav.  1*3. 
The  mixture  should  be  allowed  to  remain  at  ordinary  temperature  for  about 
an  hour  (Eder). 

Heat  is  now  applied  to  that  part  of  the  sand-bath  immediately  beneath 
the  larger  flask,  and  the  mixture  is  gradually  raised  to  the  boiling  point. 
When  distillation  has  actually  commenced,  the  water  in  the  second  flask  is 
made  to  boil  gently ;  by  this  arrangement  the  fluid  is  twice  distilled,  and  any 
traces  of  fixed  alkali  which  may  escape  the  first  are  sure  to  be  retained  in  the 
second  flask.  The  distillation  with  the  quantities  above  named  will  occupy 
about  an  hour  and  a  half,  and  is  completed  when  hydrogen  is  pretty  freely 
liberated  as  the  potash  becomes  concentrated.  The  lamp  is  then  removed, 
and  the  whole  allowed  to  cool,  the  distilling  tube  rinsed  into  the  receiver, 
also  the  tube  containing  broken  glass  ;. the  contents  of  the  receiver  are  then 
titrated  with  -£$  caustic  potash  or  soda  as  usual. 

Eder  recommends  that  an  ordinary  retort,  with  its  beak  set  upwards, 
should  be  used  instead  of  the  flask  for  holding  the  nitrate,  and  that  an 
aspirator  should  be  attached  to  the  exit  tube,  so  that  a  current  of  air  may  be 
drawn  through  during  and  after  the  distillation. 

Chlorides  and  sulphates  do  not  interfere  with  the  accuracy  of 
the  results.  Harcourt,  Eder,  and  many  others,  including  myself, 
have  obtained  very  satisfactory  results  by  this  method. 

Siewert  has  suggested  a  modification  of  this  process.  The  dis- 
tilling apparatus  is  a  300 — 350  c.c.  flask  with  tube  leading  to  two 
small  flasks  connected  together  as  wash  bottles,  and  containing 
standard  acid.  For  1  gm.  of  nitre,  4  gm.  of  iron,  and  10  gm.  of 
zinc  filings,  with  16  gm.  of  caustic  potash,  and  100  c.c.  of  alcohol  of 
sp.  gr.  0'825  are  necessary.  After  digesting  for  half  an  hour  in  the 
cold  or  in  slight  warmth,  a  stronger  heat  may  be  applied  to  drive 
out  all  the  ammonia  into  the  acid  flasks.  Finally,  10 — 15  c.c.  of 
fresh  alcohol  are  admitted  to  the  distilling  flask,  and  distilled  off 
to  drive  over  the  last  traces  of  ammonia,  and  the  acid  solution  then. 

Q  2 


228  VOLUMETRIC  ANALYSIS.  §    67. 

titrated  residually  as  usual.  The  alcohol  is  used  to  prevent  bumping, 
but  this  is  also  avoided  in  the  original  process  by  adopting  the 
current  of  air  recommended  by  Eder. 

The  copper-zinc  couple  devised  by  Gladstone  and  Tribe  has 
been  used  by  Thorp  for  the  reduction  of  nitrates  and  nitrites 
occurring  in  water  residues,  etc.  (/.  C.  S.  1873,  545).  The 
resulting  ammonia  is  distilled  into  weak  hydrochloric  acid,  and  an 
aliquot  portion  then  Nesslerized  in  the  usual  way. 

M.  W.  Williams  (/.  C.  S.  1881,  100)  has  shown  that  this 
reduction,  in  the  case  of  small  quantities  of  nitric  or  nitrous  acids, 
may  be  carried  on  by  mere  digestion  with  a  properly  arranged 
couple  at  ordinary  temperatures,  and  may  safely  be  hastened  by 
increasing  the  temperature  to  about  25°  C.  in  the  presence  of  cer- 
tain saline  or  acid  substances ;  alkaline  substances,  on  the  contrary, 
retard  the  action.  The  details  are  further  described  in  Part  VI. 


4.    By  Oxidation  of  Ferrous  Salts  (Pelouze).    Not  available  in  the 
presence  of  Org-anic  Matter. 

The  principle  upon  which  this  well-known  process  is  based  is  as 
follows : — 

(a)  When  a  nitrate  is  brought  into  contact  with  a  solution  of 
ferrous  oxide,  mixed  with  free  hydrochloric  acid,  and  heated,  part 
of  the  oxygen  contained  in  the  nitric  acid  passes  over  to  the  iron, 
forming  a  persalt,  while  the  base  combines  with  hydrochloric  acid, 
and  nitric  oxide  (NO2)  is  set  free.  3  eq.  iron  =  168  are  oxidized  by 
1  eq.  nitric  acid  =  63.  If,  therefore,  a  weighed  quantity  of  the 
nitrate  be  mixed  with  an  acid  solution  of  ferrous  chloride  or  sul- 
phate of  known  strength,  in  excess,  and  the  solution  boiled,  to 
expel  the  liberated  nitric  oxide,  then  the  amount  of  unoxidized 
iron  remaining  in  the  mixture  found  by  a  suitable  method  of 
titration,  the  quantity  of  iron  converted  from  ferrous  into  ferric 
oxide  will  be  the  measure  of  the  original  nitric  acid  in  the  propor- 
tion of  168  to  63 ;  or  by  dividing  63  by  168,  the  factor  0 "3 7 5  is 
obtained,  so  that  if  the  amount  of  iron  changed  as  described  be 
multiplied  by  this  factor,  the  product  will  be  the  amount  of  nitric 
acid  present. 

This  method,  though  theoretically  perfect,  is  in  practice  liable  to 
serious  errors,  Bowing  to  the  readiness  with  which  a  solution  of 
ferrous  oxide  absorbs  oxygen  from  the  atmosphere.  On  this 
account  accurate  results  are  only  obtained  by  conducting  hydrogen 
or  carbonic  acid  gas  through  the  apparatus  while  the  boiling  is 
carried  on.  This  modification  has  been  adopted  by  Fresenius 
with  very  satisfactory  results. 

The  boiling  vessel  may  consist  of  a  small  tubulated  retort,  supported  in 
such  a  manner  that  its  neck  inclines  upward :  a  cork  is  fitted  into  the 
tubulure,  and  through  it  is  passed  a  small  tube  connected  \\ith  a  vessel  for 


.§  67.  NITKATES.  229 

generating  either  carbonic  acid  or  hydrogen.  If  a  weighed  quantity  of  pure 
metallic  iron  is  used  for  preparing  the  solution,  the  washed  carbonic  acid  or 
hydrogen  should  be  passed  through  the  apparatus  while  it  is  being  dissolved ; 
the  solution  so  obtained,  or  one  of  double  sulphate  of  iron  and  ammonia  of 
known  strength,  being  already  in  the  retort,  the  nitrate  is  carefully  introduced, 
and  the  mixture  heated  gently  by  a  small  lamp,  or  by  the  water  bath,  for  ten 
minutes  or  so,  then  boiled  until  the  dark-red  colour  of  the  liquid  disappears, 
and  gives  place  to  the  brownish-yellow  of  ferric  compounds.  The  retort  is 
then  suffered  to  cool,  the  current  of  carbonic  acid  or  hydrogen  still  being 
kept  up,  then  the  liquid  diluted  freely,  and  titrated  with  ^  permanganate. 

Owing  to  the  irregularities  attending  the  use  of  permanganate 
with  hydrochloric  acid,  it  is  preferable,  in  case  this  acid  has  been 
used,  to  dilute  the  solution  less,  and  titrate  with  bichromate.  Two 
grams  of  pure  iron,  or  its  equivalent  in  double  iron  salt,  0*5  gni.  of 
saltpetre,  and  about  60  c.c.  of  strong  hydrochloric  acid,  are  con- 
venient proportions  for  the  analysis. 

Eder  (Z.  a.  C.  xvi.  267)  has  modified  Fresenius'  improve- 
ments as  follows : — 

1'5  gm.  of  very  thin  iron  wire  is  dissolved  in  30  to  40  c.c.  of  pure  fuming 
hydrochloric  acid,  placed  in  a  retort  of  about  200  c.c.  capacity ;  the  beak  of 
the  retort  points  upwards,  at  a  moderately  acute  angle,  and  is  connected  with 
a  U-tube,  which  contains  water.  Solution  of  the  iron  is  hastened  by  apply- 
ing a  small  flame  to  the  retort.  Throughout  the  entire  process  a  stream  of 
CO'2  is  passed  through  the  apparatus.  When  the  iron  is  all  dissolved  the 
solution  is  allowed  to  cool,  the  stream  of  CO2  being  maintained ;  the  weighed 
quantity  of  nitrate  contained  in  a  small  glass  tube  (equal  to  about  0'2  gm. 
HNO3)  is  then  quickly  passed  into  the  retort  through  the  neck ;  the  heating 
is  continued  under  the  same  conditions  as  before,  until  the  liquid  assumes 
the  colour  of  ferric  chloride.  The  whole  is  allowed  to  cool  in  a  stream  of 
CO2 ;  water  is  added  in  quantity,  and  the  unoxidized  iron  is  determined  by 
titration  with  permanganate.  The  results  are  exceedingly  good. 

If  the  CO2  be  generated  in  a  flask,  with  a  tube  passing  down- 
wards for  the  reception  of  the  acid,  air  always  finds  its  way  into  the 
retort,  and  the  results  are  unsatisfactory.  Eder  recommends  the 
use  of  Kipp's  CO2  apparatus.  By  carrying  out  the  operation 
exactly  as  is  now  to  be  described,  he  has  obtained  very  good  results 
with  ferrous  sulphate  in  place  of  chloride. 

The  same  apparatus  is  emp^ed ;  the  tube  through  which  CO2  enters  the 
retort  passes  to  the  bottom  of  the  liquid  therein,  and  the  lower  extremity  of 
this  tube  is  drawn  out  to  a  fine  point.  The  bubbles  of  CO2  are  thus  reduced 
in  size,  and  the  whole  of  the  nitric  oxide  is  removed  from  the  liquid  by  the 
passage  of  these  bubbles.  The  iron  Avire  is  dissolved  in  excess  of  dilute 
sulphuric  acid  (strength  1  :  3  or  1  :  4).  When  the  liquid  in  the  retort  has 
become  cold,  a  small  tube  containing  the  nitrate  is  quickly  passed,  by  means 
of  a  piece  of  platinum  wire  attached  to  it,  through  the  tubulus  of  the  retort, 
and  the  cork  is  replaced  before  the  tube  has  touched  the  liquid;  CO2  is  again 
passed  through  the  apparatus  for  some  time,  after  which,  by  slightly  loosening 
the  cork,  the  tube  containing  the  nitrate  is  allowed  to  fall  into  the  liquid. 
The  whole  is  allowed  to  remain  at  the  ordinary  temperature  for  about  an 
hour — this  is  essential — after  which  time  the  contents  of  the  retort  are  heated 
to  boiling,  CO2  being  passed  continuously  into  the  retort,  and  the  boiling 
continued  till  the  liquid  assumes  the  light  yellow  colour  of  ferric  sulphate. 


230  VOLUMETRIC  ANALYSIS.  §    67. 

After  cooling,  water  is  added  (this  may  be  omitted  "with  bichromate),  aud  the 
unoxidized  iron  is  determined  by  means  of  permanganate. 

Eder  also  describes  a  slight  modification  of  this  process,  allowing 
of  the  use  of  a  flask  in  place  of  the  retort,  and  of  ammonio-ferrous 
sulphate  in  place  of  iron  wire.  Although  the  titration  with  per- 
manganate is  more  trustworthy  when  sulphuric  acid  is  employed 
than  when  hydrochloric  acid  is  used,  he  nevertheless  thinks  that  the 
use  of  ferrous  chloride  is  generally  to  be  recommended  in  preference 
to  that  of  ferrous  sulphate.  When  the  chloride  is  employed,  no 
special  concentration  of  acid  is  necessary ;  the  nitric  oxicle  is  more 
readily  expelled  from  the  liquid,  and  the  process  is  finished  in  a 
shorter  time. 

The  final  point  in  the  titration  with  permanganate,  when  the 
sulphate  is  employed,  is  rendered  more  easy  of  determination  by 
adding  a  little  potassic  sulphate  to  the  liquid. 

(5)  Direct  titration  of  the  resulting-  Ferric  salt  by  Stannous 
Chloride. — Fresenius  has  adopted  the  use  of  stannous  chloride  for 
titrating  the  ferric  salt  with  very  good  results. 

The  following  plan  of  procedure  is  recommended  by  the  same 
authority. 

A  solution  of  ferrous  sulphate  is  prepared  by  dissolving  100  gm.  of  the 
crystals  in  500  c.c.  of  hydrochloric  acid  of  spec.  grav.  I'lO  ;  when  used  for  the 
analysis,  the  small  proportion  of  ferric  oxide  invariably  present  in  it  is  found 
by  titrating  with  stannous  chloride,  as  in  §  60.1.  The  nitrate  being  weighed 
or  measured,  is  brought  together  with  50  c.c.  (more  or  less,  according  to  the 
quantity  of  nitrate)  of  the  iron  solution  into  a  long-necked  flask,  through 
the  cork  of  which  two  glass  tubes  are  passed,  one  connected  with  a  CO2 
apparatus,  and  reaching  to  the  middle  of  the  flask,  the  other  simply  an  outlet 
for  the  passage  of  the  gas.  When  the  gas  has  driven  out  all  the  air,  the  flask 
is  at  first  gently  heated,  and  eventually  boiled,  to  dispel  all  the  nitric  oxide. 
The  CO2  tube  is  then  rinsed  into  the  flask,  and  the  liquid,  while  still  boiling- 
hot,  titrated  for  ferric  chloride,  as  in  §  60.1. 

The  liquid  must,  however,  be  suffered  to  cool  before  titrating 
with  iodine  for  the  excess  of  stannous  chloride.  While  cooling, 
the  stream  of  CO2  should  still  be  continued.  The  quantity  of  iron 
changed  into  peroxide,  multiplied  by  the  factor  0*375,  will  give  the 
amount  of  nitric  acid. 

Example :  (1)  A  solution  of  stannous  chloride  was  used  for  titrating 
10  c.c.  of  solution  of  pure  ferric  chloride  containing  0'215075  gm.  Ee. 
25'65  c.c.  of  tin  solution  were  required,  therefore  that  quantity  was  equal  to 
0-0807  gm.  of  HNO3,  or  0'069131  gm.  of  N2^.  _ 

(2)  50  c.c.  of  acid  ferrous  sulphate  were  titrated  with  tin  solution  for 
ferric  oxide,  and  0'24  c.c.  was  required. 

(3)  1  c.c.  tin  solution=3'3  c.c.  iodine  solution. 

(4)  0'2177  gm.  of  pure  nitre  was  boiled,  as  described,  with  50  c.c.  of  the 
acid  ferrous  sulphate,  and  required  45'03  c.c.  tin  solution,  and  4'7  c.c.  iodine — 

4'7  c.c.  iodine  solution  =1*42  c.c.  SnCl2 

The  peroxide  in  the  protosulphate  solution=0'24  c.c. 

~ 


§    67.  NITRATES.  231 

45-03— 1-66=43-37,  therefore  25'65  :  0'069131-=43'37  :  a?,=01169  N2O5 
instead  of  0'1163,  or  53'69  per  cent,  instead  of  53'41.  A  mean  of  this,  with 
three  other  estimations,  using  variable  proportions  of  tin  and  iron  solutions, 
gave  exactly  53*41  per  cent.  The  process  is  therefore  entirely  satisfactory  in 
the  case  of  pure  materials. 

The  above  process  is  slightly  modified  by  Eder.  About  10  gm. 
of  ammonio-ferrous  sulphate  are  dissolved  in  a  flask,  in  about  50  c.c. 
of  hydrochloric  acid  (sp.  gr.  1*07)  in  a  stream  of  CO2.  The  tube 
through  which  the  CO2  enters  is  drawn  to  a  point ;  an  exit-tube, 
somewhat  trumpet-shaped,  to  admit  of  any  liquid  that  may  spirt 
finding  its  way  back  into  the  flask  passes  downwards  into  water. 
After  solution  of  the  double  salt,  the  nitrate  is  dropped  in  with 
the  precautions  already  detailed,  and  the  liquid  is  boiled  until  the 
nitric  oxide  is  all  expelled.  The  hot  liquid  is  diluted  with  twice 
its  own  volume  of  water,  excess  of  standard  stannous  chloride 
solution  is  run  in,  the  whole  is  allowed  to  cool  in  a  stream  of  CO2, 
and  the  excess  of  tin  is  determined  by  means  of  standard  iodine. 

(c)  Holland's  ModiScation  of  the 
Pelouze  process. — The  arrangement  of 
apparatus  shown  in  fig.  38  obviates  the 
use  of  an  atmosphere  of  H  or  CO2.  A  is  a 
long-necked  assay  flask  drawn  off  at  B,  so 
as  to  form  a  shoulder,  over  which  is  passed 
a  piece  of  stout  pure  india-rubber  tube, 
D,  about  6  centimeters  long,  the  other  end 
terminating  in  a  glass  tube,  F,  drawn  off 
so  as  to  leave  only  a  small  orifice.  On 
the  elastic  connector  D  is  placed  a  screw 
clamp.  At  c,  a  distance  of  3  centimeters 
Fig.  38.  from  the  shoulder,  is  cemented  with  a 

blow-pipe  a  piece  of    glass  tube   about  2 

centimeters  long,  surmounted  by  one  of  stout  elastic  tube  rather 
more  than  twice  that  length.  The  elastic  tubes  must  be  securely 
attached  to  the  glass  by  binding  with  wire.  After  binding,  it  is  as 
well  to  turn  the  end  of  the  conductor  back  and  smear  the  inner 
surface  with  fused  caoutchouc,  and  then  replace  it  to  render  the 
joint  air-tight. 

The  Analysis :  A  small  funnel  is  inserted  into  the  elastic  tube  at  c,  the 
clamp  at  D  being  for  the  time  open ;  after  the  introduction  of  the  solution, 
followed  by  a  little  water  which  washes  all  into  the  flask,  the  funnel  is 
removed,  and  the  flask  supported  by  means  of  the  wooden  clamp,  in  the 
inclined  position  it  occupies  in  the  figure.  The  contents  are  now  made  to 
boil  so  as  to  expel  all  air  and  reduce  the  volume  of  the  fluid  to  about  4  or 
5  c.c.  "When  this  point  is  reached  a  piece  of  glass  rod  is  inserted  into  the 
elastic  tube  at  c,  which  causes  the  water  vapour  to  escape  through  F. 

Into  the  small  beaker  is  put  about  50  c.c.  of  a  previously  boiled  solution  of 
ferrous  sulphate  in  hydrochloric  acid  (the  amount  of  iron  already  existing 
as  persalt  must  be  known). 

The  boiling  is  still  continued  for  a  moment  to  ensure  perfect  expulsion  of 


232  VOLUMETRIC   ANALYSIS.  .§    67. 

air  from  F,  the  lamp  is  then  removed,  and  the  caoutchouc  connector  slightly 
compressed  with  the  first  finger  and  thumb  of  the  left  hand.  As  the  flask 
cools  the  solution  of  iron  is  drawn  into  it ;  when  the  whole  has  nearly  receded 
the  elastic  tube  is  tightly  compressed  with  the  fingers,  whilst  the  sides  of  the 
beaker  are  washed  with  a  jet  of  boiled  water,  which  is  also  allowed  to  pass 
into  the  flask.  The  washing  may  be  repeated,  taking  care  not  to  dilute  more 
than  is  necessary  or  admit  air.  Whilst  F  is  still  full  of  water,  the  elastic 
connector  previously  compressed  with  the  fingers  is  now  securely  closed  with 
the  clamp,  the  screw  of  which  is  worked  with  the  right  hand.  Provided 
the  clamp  is  a  good  one,  F  will  remain  full  of  water  during  the  subsequent 
digestion  of  the  flask. 

After  heating  in  a  water  bath  at  100°  for  half  an  hour,  the  flask  is  removed 
from  the  water  bath  and  cautiously  heated  with  a  small  flame,  the  fingers  at 
the  same  time  resting  on  the  elastic  connector  at  the  point  nearest  the 
shoulder ;  as  soon  as  the  tube  is  felt  to  expand,  owing  to  the  pressure  from 
within,  the  lamp  is  removed  and  the  screw  clamp  released,  the  fingers  main- 
taining a  secure  hold  of  the  tube,  the  gas-flame  is  again  replaced,  and  when 
the  pressure  on  the  tube  is  again  felt,  this  latter  is  released  altogether,  thus 
admitting  of  the  escape  of  the  nitric  oxide  through  F,  which  should  be 
below  the  surface  of  water  in  the  beaker  whilst  these  manipulations  are 
performed.  The  contents  of  the  flask  are  now  boiled  until  the  nitric  oxide 
is  entirely  expelled,  and  the  solution  of  iron  shows  only  the  brown  colour  of 
the  perchloride.  At  the  completion  of  the  operation  the  beaker  is  first 
removed,  and  then  the  lamp. 

It  now  only  remains  to  transfer  the  ferric  solution  to  a  suitable  vessel,  and 
determine  the  perchloride  with  stannous  chloride  as  in  b. 

A  mean  of  six  experiments  for  the  percentage  determination  of 
N205  in  pure  nitre  gave  53*53  per  cent,  instead  of  53 '41.  The 
process  is  easy  of  execution,  and  gives  satisfactory  results.  The 
point  chiefly  requiring  attention  is  that  the  apparatus  should  be 
air-tight,  which  is  secured  by  the  use  of  good  elastic  tubes  and 
clamp. 


5.     Schlosing's    Method    (available    in    the    presence    of   Org-anic 

Matter). 

The  solution  of  nitrate  is  boiled  in  a  flask  till  all  air  is  expelled, 
then  an  acid  solution  of  ferrous  chloride  drawn  in,  the  mixture 
boiled,  and  the  nitric  oxide  gas  collected  over  mercury  in  a  balloon 
filled  with  mercury  and  milk  of  lime ;  the  gas  is  then  brought, 
without  loss,  in  contact  with  oxygen  and  water,  so  as  to  convert  it 
again  into  nitric  acid,  then  titrated  with  -^  alkali  as  usual. 

This  method  was  devised  by  Sch  losing  for  the  estimation  of 
nitric  acid  in  tobacco,  and  is  especially  suitable  for  that  and  similar 
purposes,  where  the  presence  of  organic  matter  would  interfere  with 
the  direct  titration  of  the  iron  solution.  Where  the  quantity  of 
nitric  acid  is  not  below  0*15  gm.  the  process  is  fairly  accurate,  but 
needs  a  special  and  rather  complicated  arrangement  of  apparatus, 
the  description  of  which  may  be  found  in  the  original  paper  in 
Annal.  de  Chim.  [3]  xl.  479,  or  in  Fresenius'  Quant.  Anal,  sixth 
edition. 

An  arrangement  of  apparatus,  dispensing  with  the  use  of  mercury, 


67. 


NITRATES, 


233 


has  been  designed  by  Wild t  and  Scheibe  (Z.  a  C.  xxiii.  151), 
which  simplifies  the  analysis  and  gives  accurate  results  with  not 
less  than  O25  gm.  X205.  With  smaller  quantities  the  results  are 
too  low.  Fig.  39  shows  the  apparatus  used. 


Fig.  39. 

A  is  an  Erlenmeyer's  flask  of  250  c.c.  capacity,  containing 
the  solution  to  be  analyzed.  B  is  a  round-bottomed  flask  of 
250 — 300  c.c.  capacity,  half  filled  with  caustic  soda,  to  absorb  any 
HC1  which  might  be  carried  over  from  A.  C  is  an  Erlenmeyer's 
flask  of  750  c.c.  capacity,  containing  a  little  water  to  absorb  the 
nitric  acid.  D  is  a  tube,  containing  water  to  collect  any  nitric 
acid  not  absorbed  by  the  water  in  C.  The  tube  d  is  bent,  as  shown 
in  the  diagram,  and  drawn  out  to  a  point,  to  diminish  the  size  of 
the  bubbles.  The  tube  e  is  wide,  and  cut  obliquely  to  prevent 
water  collecting  and  passing  into  C. 

The  Analysis :  The  clip  b  is  closed  and  c  opened,  and  the  tube  e 
disconnected  from  /.  The  solutions  in  A  and  B  are  then  boiled  for 
20  minutes  to  remove  all  oxygen.  The  tubes  e  and  /  are  again  con- 
nected, the  clip  c  is  closed,  the  flame  under  B  increased  to  prevent  the 
liquid  in  C  from  being  drawn  back,  and  the  clip  b  is  opened.  As  soon  as 
steam  issues  from  the  tube  a,  it  is  dipped  into  a  conical  glass  containing 
50  c.c.  of  ferrous  chloride  prepared  according  to  Schlosing's  directions, 
and  the  flame  under  A  is  removed,  when  the  ferrous  chloride  enters  the  flask. 
The  clip  b  is  regulated  with  the  finger  and  thumb,  so  as  to  prevent  the  entry 
of  air  into  the  flask.  The  conical  vessel  is  rinsed  two  or  three  times  with 


234  VOLUMETRIC  ANALYSIS.  §    67. 

water,  and  this  is  allowed  to  enter  the  flask,  and  the  clip  6  is  then  closed, 
and  the  vessel  A  heated.  The  liquid  in  A  turns  brown  in  a  short  time,  and 
nitric  oxide  is  evolved.  The  clip  c  is  opened  slightly  from  time  to  time 
until  the  pressure  is  high  enough,  when  it  is  opened  entirely.  The  flames 
must  be  regulated  so  that  a  slow  current  of  gas  bubbles  through  the  water  in 
C.  The  hydrochloric  acid  is  removed  by  the  caustic  soda  in  B,  and  the 
nitric  oxide  on  coming  in  contact  with  the  air  in  C  is  oxidized,  and  the  nitric 
acid  absorbed  by  the  water.  In  case  the  current  of  gas  is  too  rapid,  the 
escaping  nitric  acid  is  absorbed  in  D.  After  an  hour  the  tubes  e  and  /are 
disconnected,  while  the  solutions  in  A  and  B  are  still  boiling,  and  the  nitric 
acid  is  titrated  with  dilute  caustic  soda  (about  £  normal).  The  vessel  C 
must  be  well  cooled  during  the  whole  experiment,  which  occupies  about  an 
hour  and  a  half. 

Good  results  were  obtained  with  nitrates  of  potash  and  soda, 
both  alone  and  mixed  with  ammonium  sulphate,  superphosphate, 
and  amido  compounds.  "With  superphosphate  the  solution  should 
be  made  slightly  alkaline,  to  prevent  the  liberation  of  nitric  acid. 

Warington  (/.  C.  S.  1880,  468)  has  made  a  series  of  experi- 
ments on  the  original  Schlosing  process,  for  the  purpose  of 
testing  its  accuracy,  when  small  quantities  of  nitric  acid  have  to  be 
determined  in  the  presence  of  organic  substances,  such  for  instance 
as  in  soils,  the  sap  of  beet-root,  etc. ;  but  instead  of  converting  the 
nitric  oxide  back  into  nitric  acid  as  in  the  original  method,  he 
collected  the  gas  either  over  caustic  soda  as  recommended  by 
Reich ardt,  or  over  mercury,  and  ascertained  its  amount  by 
measurement  in  Frankland's  gas  apparatus.  The  results  obtained 
by  Warington  plainly  showed  that  even  on  the  most  favourable 
circumstances  the  method  as  usually  worked  in  Germany,  either  by 
the  alkalimetric  titration  or  by  measurement  of  the  gas,  invariably 
gave  results  much  too  low,  especially  if  the  quantity  of  nitrate 
operated  on  was  small,  say  5  or  6  centigrams  of  nitre ;  moreover, 
Avhen  sugar  or  similar  organic  substance  was  present  the  resulting 
gas  was  very  impure,  and  the  distillates  were  highly  coloured  from 
the  presence  of  some  volatile  products.  The  nitric  oxide  also 
suffered  considerable  diminution  of  volume,  when  left  for  any  time 
in  contact  with  the  distillate,  especially  when  over  caustic  soda. 
This  being  the  case,  the  following  modification  originally  recom- 
mended by  Schlosing  was  adopted,  in  which  CO2  was  employed, 
both  to  assist  in  expelling  the  air  from  the  apparatus,  and  to  chase 
out  the  nitric  oxide  produced. 

The  form  of  apparatus  adopted  by  Warington  is  shown  in 
%.  40.  The  vessel  in  which  the  reaction  takes  place  is  a  small 
tubulated  receiver,  the  tubulure  of  which  has  been  bent  near  its 
extremity  to  make  a  convenient  junction  with  the  delivery  tube, 
which  dips  into  a  trough  of  mercury  on  the  left.  The  long  supply 
tube  attached  to  the  receiver  is  of  small  bore,  and  is  easily  filled  by 
a  J  c.c.  of  liquid.  The  short  tube  to  the  right  is  also  of  small  bore, 
and  is  connected  by  a  caoutchouc  tube  and  clamp  with  an  apparatus 
for  the  continuous  production  of  carbonic  acid. 

In  using   this  apparatus  the   supply  tube   is   first   filled  with 


§  67. 


NITRATES. 


235 


strong  HC1,  and  CO2  is  passed  through  the  apparatus  till  a  portion 
of  the  gas  collected  in  a  jar  over  mercury  is  found  to  be  entirely 
absorbed  by  caustic  potash.  The  current  of  gas  is  then  stopped 
by  closing  the  clamp  to  the  right.  A  chloride  of  calcium  bath  at 
140°  is  next  brought  under  the  receiver,  which  is  immersed  one- 
half  or  more  in  the  hot  fluid ;  the  temperature  of  the  bath  is 
maintained  throughout  the  operation  by  a  gas-burner  placed  beneath 
it.  By  allowing  a  few  drops  of  HC1  to  enter  the  hot  receiver,  the 
CO2  it  contains  is  almost  entirely  expelled.  A  jar  filled  with 


Tig.  40. 

mercury  is  then  placed  over  the  end  of  the  delivery  tube,  and  all 
is  ready  for  the  commencement  of  a  determination. 

The  nitrate,  which  should  be  in  the  form  of  a  dry  residue  in  a 
small  beaker  or  basin,  is  dissolved  in  about  2  c.c.*  of  strong  ferrous 
chloride  solution,  1  c.c.  of  strong  HC1  is  added,  and  the  whole  is 
then  introduced  into  the  receiver  through  the  supply  tube,  being 
followed  by  successive  rinsings  with  HC1,  each  rinsing  not  exceed- 
ing a  J  c.c.,  as  the  object  is  to  introduce  as  small  a  bulk  of  liquid 
as  possible.  The  contents  of  the  receiver  are  in  a  few  minutes 
boiled  to  dryness;  a  little  CO2  is  admitted  before  dryness 


IS 


*  Supposing  the  ferrous  chloride  to  contain  2  gni.  of  iron  per  10  c.c.,  then  1  c.c.  of 
the  solution  will  be  nearly  equivalent  to  0'12  gin.  of  nitre,  or  0'016G  gm.  of  nitrogen. 
A  considerable  excess  of  iron  should,  however,  always  be  used. 


236  VOLUMETRIC  ANALYSIS.  .§    67. 

reached,  and  again  afterwards  to  drive  over  all  remains  of  nitric 
oxide.  If  the  gas  will  not  be  analyzed  till  next  day,  it  is  advisable 
to  use  more  CO2,  so  as  to  leave  the  nitric  oxide  diluted  with  several 
times  its  volume  of  that  gas.  As  soon  as  one  operation  is  concluded 
the  apparatus  is  ready  for  another  charge. 

This  mode  of  working  presents  the  following  advantages  : — 

(1)  The  volume  of  liquid  introduced  into  the  apparatus  is  much 
diminished,  and  with  this  of  course  the  amount  of  dissolved  air 
contributed  from  this  source. 

(2)  By  evaporation  to  dryness  a  complete  reaction  of  the  nitrate 
and  ferrous  chloride,  and  a  perfect  expulsion  of  the  nitric  oxide 
formed,  is  as  far  as  possible  attained. 

(3)  The  nitric  oxide  in  the  collecting  jar  is  left  in  contact  with 
a   much   smaller   volume   of    acid   distillate,  and   its   liability  to 
absorption  is  greatly  diminished  by  its  dilution  with  CO2. 

The  results  obtained  with  this  apparatus  by  Warington  on 
small  quantities  of  nitre  alone,  and  mixed  with  variable  quantities 
of  ammonic  salts  and  organic  substances  including  sugar,  showed  a 
marked  improvement  upon  the  method  as  usually  carried  out. 

A  further  improvement  has  been  made  in  this  method  by 
Warington  (/.  C.  S.  1882,  345),  and  described  by  him  as 
follows : — 

The  apparatus  now  employed  is  quite  similar  to  that  shown  in  fig.  40,  with 
the  only  difference  that  the  bulb  retort  in  which  the  reaction  takes  place  is 
now  only  If  inch  in  diameter,  thus  more  exactly  resembling  the  form 
employed  by  Sch  16 sing.  A  bulb  of  this  size  is  sufficient  for  the  analysis 
of  soil  extracts ;  for  determinations  of  nitrates  in  vegetable  extracts  a  larger 
bulb  is  required. 

The  chief  improvement  consists  in  the  use  of  CO2  as  free  as  possible  from 
oxygen.  The  generator  is  formed  of  two  vessels.  The  lower  one  consists  of 
a  bottle  with  a  tubulure  in  the  side  near  the  bottom ;  this  bottle  is  supported 
in  an  inverted  position,  and  contains  the  marble  from  which  the  gas  is 
generated.  The  upper  vessel  consists  of  a  similar  bottle  standing  upright ; 
this  contains  the  HC1  required  to  act  on  the  marble.  The  two  vessels  are 
connected  by  a  glass  tube  passing  from  the  side  tubulure  of  the  upper  vessel 
to  the  inverted  mouth  of  the  lower  vessel ;  the  acid  from  the  upper  vessel 
thus  enters  below  the  marble.  CO2  is  generated  and  removed  at  pleasure  by 
opening  a  stop-cock  attached  to  the  side  tubulure  of  the  lower  vessel,  thus 
allowing  HC1  to  descend  and  come  in  contact  with  the  marble.  The  fragments 
of  marble  used  have  been  previously  boiled  in  water.  The  boiling  is  con- 
ducted in  a  strong  flask.  After  boiling  has  proceeded  some  time,  a  caoutchouc 
stopper  is  fixed  in  the  neck  of  the  flask,  and  the  flame  removed ;  boiling  will 
then  continue  for  some  time  in  a  partial  vacuum.  The  lower  reservoir  is 
nearly  filled  with  the  boiled  marble  thus  prepared.  The  HC1  has  been  also 
well  boiled,  and  before  it  is  introduced  into  the  upper  reservoir  it  has  dissolved 
in  it  a  moderate  quantity  of  cuprous  chloride.  As  soon  as  the  acid  has  been 
placed  in  the  upper  reservoir  it  is  covered  by  a  layer  of  oil.  The  apparatus 
being  thus  charged  is  at  once  set  in  active  work  by  opening  the  stop-cock  of 
the  marble  reservoir ;  the  acid  descends,  enters  the  marble  reservoir,  and  the 
CO2  produced  drives  out  the  air  which  is  necessarily  present  at  starting.  As 
the  acid  reservoir  is  kept  on  a  higher  level  than  the  marble  reservoir,  the 
latter  is  always  under  internal  pressure,  and  leakage  of  air  from  without 
cannot  occur. 


§  67.  NITKATES.  237 

The  presence  of  the  cuprous  chloride  in  the  hydrochloric  acid  not  only 
ensures  the  removal  of  dissolved  oxygen,  but  affords  an  indication  to  the  eye 
of  the  maintenance  of  this  condition.  So  long  as  the  acid  remains  of  an 
olive  tint,  oxygen  will  be  absent;  but  should  the  acid  become  of  a  clear 
blue-green,  it  is  no  longer  certainly  free  from  oxygen,  and  more  cuprous 
chloride  must  be  added. 

A  further  slight  improvement  adopted  consists  in  the  use  of  freshly-boiled 
reagents,  which  are  employed  in  as  small  a  quantity  as  possible.  When 
boiling  the  hydrochloric  acid  it  is  well  to  add  a  few  drops  of  ferrous  chloride, 
in  order  more  certainly  to  remove  any  dissolved  oxygen. 

The  mode  of  operation  is  as  follows  : — The  apparatus  is  fitted  together,  the 
long  funnel  tube  attached  to  the  bulb  retort  being  filled  with  water. 
Connection  is  made  with  the  glass  stop-cock  of  the  CO2  generator  by  means 
of  a  short  stout  caoutchouc  tube,  provided  with  a  pinch-cock.  The  pinch- 
cock  being  opened,  the  stop-cock  is  turned  till  a  moderate  stream  of  bubbles 
rises  in  the  mercury  trough ;  the  stop-cock  is  left  in  this  position,  and  the 
admission  of  gas  is  afterwards  controlled  by  the  pinch-cock,  pressure  on 
which  allows  a  few  bubbles  to  pass  at  a  time.  The  heated  chloride  of  calcium 
bath  is  next  raised,  so  that  the  bulb  retort  is  almost  submerged;  the 
temperature,  shown  by  a  thermometer  which  forms  part  of  the  apparatus, 
should  be  130 — 140°.  By  boiling  small  quantities  of  water  or  hydrochloric 
acid  in  the  bulb  retort  in  a  stream  of  CO2  the  air  present  is  expelled ;  the 
supply  of  gas  must  be  stopped  before  the  boiling  has  ceased,  so  as  to  leave 
little  in  the  retort.  Previous  to  very  delicate  experiments  it  is  advisable  to 
introduce  through  the  funnel  tube  a  small  quantity  of  nitre,  ferrous  chloride, 
and  hydrochloric  acid,  rinsing  the  tube  with  the  latter  reagent ;  any  trace  of 
oxygen  remaining  in  the  apparatus  is  then  consumed  by  the  nitric  oxide 
formed,  and  after  boiling  to  dryness,  and  driving  out  the  nitric  oxide  with 
CO2,  the  apparatus  is  in  a  perfect  condition  for  a  quantitative  experiment. 

Soil  extracts  may  be  used  without  other  preparation  than  concentration. 
Vegetable  juices,  which  coagulate  when  heated,  require  to  be  boiled  and 
filtered,  or  else  evaporated  to  a  thin  syrup,  treated  with  alcohol  and  filtered. 
A  clear  solution  being  thus  obtained,  it  is  concentrated  over  a  water-bath  to 
the  smallest  volume,  in  a"  beaker  of  smallest  size.  As  soon  as  cool,  it  is  mixed 
with  1  c.c.  of  a  cold  saturated  solution  of  ferrous  chloride  and  1  c.c.  HC1, 
both  reagents  having  been  boiled  and  cooled  immediately  before  use.  In 
mixing  with  the  reagents  care  must  be  taken  that  bubbles  of  air  are  not 
entangled ;  this  is  especially  apt  to  occur  with  viscid  extracts.  The  quantity 
of  ferrous  chloride  mentioned  is  amply  sufficient  for  most  soil  extracts,  but 
it  is  well  perhaps  to  use  2  c.c.  in  the  first  experiment  of  a  series;  the 
presence  of  a  considerable  excess  of  ferrous  chloride  in  the  retort  is  thus 
ensured.  With  bulky  vegetable  extracts  more  ferrous  chloride  should  be 
employed ;  to  the  syrup  from  20  gm.  of  mangel  sap  should  be  added  5  c.c. 
of  ferrous  chloride,  and  2  c.c.  of  hydrochloric  acid. 

The  mixture  of  the  extract  with  ferrous  chloride  and  HC1  is  introduced 
through  the  funnel  tube,  and  rinsed  in  with  three  or  four  successive  %  c.c. 
of  HC1.  The  contents  of  the  retort  are  then  boiled  to  dryness,  a  little  CO2 
being  from  time  to  time  admitted,  and  a  more  considerable  quantity  used  at 
the  end  to  expel  any  remaining  nitric  oxide.  The  most  convenient  tem- 
perature is  140°,  but  in  the  case  of  vegetable  extracts  it  is  well  to  commence 
at  130°,  as  there  is  some  risk  of  the  contents  of  the  retort  frothing  over. 
The  gas  is  collected  in  a  small  jar  over  mercury.  As  soon  as  one  operation 
is  completed,  the  jar  is  replaced  by  another  full  of  mercury,  and  the 
apparatus  is  ready  to  receive  a  fresh  extract.  A  series  of  five  determinations, 
with  all  the  accompanying  gas  analyses,  may  be  readily  performed  in  one 
day.  The  bulb  retort  becomes  encrusted  with  charcoal  when  extracts  rich  in 
organic  matter  are  the  subject  of  analysis ;  it  is  best  cleaned  first  with  water, 
and  then  by  heating  oil  of  vitriol  in  it. 


238  VOLUMETRIC   ANALYSIS.  §    67. 

Mercury,  contrary  to  the  statement  in  most  text  books,  is  gradually 
attacked  by  hydrochloric  acid  in  the  presence  of  air ;  the  mercury  in  the 
trough  is  thus  apt  to  become  covered  with  a  grey  chloride,  and  it  is  quite 
necessary  to  keep  the  store  of  mercury  in  contact  with  sulphuric  acid  to 
preserve  its  mobile  condition. 

The  gas  analysis  is  of  a  simple  character;  the  gas  is  measured  after 
absorption  of  the  CO2  by  potash,  and  again  after  absorption  of  the  nitric 
oxide,  the  difference  giving  the  amount  of  this  gas.  For  the  absorption  of 
nitric  oxide,  a  saturated  solution  of  ferrous  chloride  was  for  some  time  em- 
ployed. This  method  is  not,  however,  perfectly  satisfactory  when  the 
highest  accuracy  is  required,  the  nitric  oxide  being  generally  rather  under- 
estimated, except  the  process  of  absorption  is  repeated  with  a  fresh  portion 
of  ferrous  chloride.  The  error  is  greater  in  proportion  to  the  quantity  of 
unabsorbed  gas  present.  Thus,  with  a  mixture  of  nitrogen  and  nitric  oxide 
containing  little  of  the  former,  absorption  of  the  nitric  oxide  by  successive 
treatment  with  oxygen  and  pyrogallol  over  potash  showed  97'8  per  cent,  of 
nitric  oxide ;  while  the  same  gas,  analyzed  by  a  single  absorption  with  ferrous 
chloride  (after  potash),  showed  97' 5  per  cent,  of  nitric  oxide.  With  a  mixture 
containing  more  nitrogen,  the  oxygen  method  showed  65'9  per  cent,  of  nitric 
oxide ;  while  one  absorption  with  ferrous  chloride  gave  64'2  per  cent.,  and 
a  second  absorption,  in  which  the  ferrous  chloride  was  plainly  discoloured, 
66  '2  per  cent.  The  use  of  ferrous  chloride  as  an  absorbent  for  nitric  oxide 
has  now  been  given  up,  and  the  oxygen  method  substituted.  All  the 
measurements  of  the  gas  are  now  made  without  shifting  the  laboratory 
vessel ;  the  conditions  are  thus  favourable  to  extreme  accuracy. 

The  chief  source  of  error  attending  the  oxygen  process  -lies  in  the 
small  quantity  of  carbonic  oxide  produced  during  the  absorption  with 
pyrogallol;  this  error  becomes  negligible  if  the  oxygen  is  only  used  in 
small  excess.  The  difficulty  of  using  the  oxygen  in  nicely  regulated 
quantity  may  be  removed  by  the  use  of  Bischof's  gas  delivery- 
tube.  This  may  be  made  of  a  test-tube,  having  a  small  perforation 
half  an  inch  from  the  mouth.  The  tube  is  partly  filled  with 
oxygen  over  mercury,  and  its  mouth  is  then  closed  by  a  finely- 
perforated  stopper,  made  from  a  piece  of  wide  tube,  and  fitted  tightly 
into  the  test-tube  by  means  of  a  covering  of  caoutchouc.  When 
this  tube  is  inclined,  the  side  perforation  being  downwards,  the 
oxygen  is  discharged  in  small  bubbles  from  the  perforated  stopper, 
while  mercury  enters  through  the  side  opening.  Using  this  tube, 
the  supply  of  oxygen  is  perfectly  under  control,  and  can  be 
stopped  as  soon  as  a  fresh  bubble  ceases  to  produce  a  red  tinge  in 
the  laboratory  vessel.  The  trials  made  with  this  apparatus  have 
been  very  satisfactory.  If  nitrites  are  to  be  estimated  by  this 
method,  it  is  necessary  first  to  convert  them  into  nitrates,  with 
excess  of  hydrogen  peroxide,  which  is  entirely  destroyed  by  the 
subsequent  evaporation  to  dryness. 

Technical  method  for  Alkaline  Nitrates  and  Nitrated  Manures. 

Wagner  uses  a  simple  arrangement  of  apparatus,  which  gives 
fairly  good  results,  and  permits  of  rapid  working. 

A  200  c.c.  flask  is  fitted  with  a  two-hole  rubber  stopper.  One  hole  carries 
an  ordinary  gas  delivery  tube,  and  the  other  a  thistle  funnel,  having  a  stop- 


§  67.  NITRATES.  239 

cock  below  the  funnel.     The  end  of  this  tube  is  narrowed,  and  does  not  quite 
reach  the  liquid  in  the  flask. 

A  solution  of  200  gm.  of  iron  wire  in  hydrochloric  acid  is  made  and 
diluted  to  1  liter.  40  c.c.  of  this  solution  is  placed  in  the  flask,  and  the  air 
expelled  by  boiling.  10  c.c.  of  a  standard  solution  of  sodic  nitrate,  con- 
taining 33  gm.  per  liter,  are  then  placed  in  the  funnel,  and  allowed  gradually 
to  drop  into  the  boiling  solution  of  iron.  A  gas  tube  graduated  to  100  c.c.  is 
filled  with  boiled  and  cooled  distilled  water,  and  the  nitric  oxide  collected  in 
the  usual  way.  When  the  nitre  solution  is  nearly  all  dropped  in,  the  funnel 
is  filled  with  20  per  cent.  HC1,  and  run  down  ;  this  is  repeated,  the  liquid 
being  still  kept  gently  boiling.  10  c.c.  of  the  solution  to  be  tested  are  now 
put  into  the  funnel,  taking  care  that  not  more  than  100  c.c.  of  gas  will  result. 
The  gas  is  collected  as  before  in  a  fresh  tube  precisely  as  in  the  case  of  the 
pure  nitrate.  In  this  manner  five  or  six  estimations  can  be  made  with  the 
one  and  the  same  ferrous  solution.  Finally  a  fresh  test  is  made  with  standard 
nitre  solution  ;  the  readings  of  the  tubes  are  taken,  and  as  they  will  all  be  of 
same  temperature  and  pressure  no  correction  is  necessary,  all  being  allowed 
to  cool  to  the  same  point. 

The  calculation  is  easy.  Suppose  that  the  pure  nitre  gave  90  c.c. 
of  gas,  this  volume  =  0-33  gm.  of  NaNO3,  or  1  c.c.  =  0-00366 
gm.  =  0-000604  gm.  N. 

6.     Estimation   by   Standard   Indigro    Solution. 

This  process  has  commanded  a  great  deal  of  attention  as  a  ready 
and  convenient  one  for  estimating  the  nitrogen  existing  as  nitrates 
and  nitrites  in  waters,  etc.,  but  it  is  subject  to  great  irregularity 
unless  conducted  with  special  precautions.  The  principle  of  the 
method  is  that  of  liberating  free  nitric  and  nitrous  acids  from  their 
combinations  by  the  aid  of  strong  sulphuric  acid,  and  measuring 
the  quantity  so  liberated  by  the  decoloration  of  a  solution  of  indigo. 

As  a  general  rule,  in  the  case  of  waters,  no  amount  of  inter- 
ference is  produced  by  the  presence  of  chlorides,  sulphates,  or 
alkaline  and  earthy  matters  usually  found. 

In  the  third  edition  of  this  book,  the  process,  as  modified  by 
Thorp  and  myself,  was  given;  but  since  that  time  War  ing  ton 
has  extensively  experimented  on  the  method  with  great  discrimina- 
tion, and  found  out  its  weak  points,  the  result  being  that  when  the 
method  is  carried  out  in  the  way  adopted  by  him  in  the  case  of 
potable  waters,  drainage  waters,  soil  extracts,  etc.,  in  the  absence 
of  much  organic  matter,  very  concordant  results  are  obtained, 
differing  very  slightly  from  other  established  methods.  These 
valuable  contributions  by  Warington  are  given  in  two  papers 
(C.  N.  xxxv.  45,  and  /.  G.  S.  1879,  578),  and  may  be  summarized 
as  follows  :  — 

Standard  Potassic  Nitrate.  —  I'Oll  gm.  of  the  pure  salt  in  a 
liter.  This  is  in  reality  a  —  ^  solution  of  nitre. 


Weak  Standard  Nitre.  —  One  part  of  the  above  solution  to  three 
parts  of  water. 


240  VOLUMETRIC  ANALYSIS.  §    67. 

A  series  of  weaker  solutions  of  nitre  are  also  requisite  for  standard- 
izing the  indigo,  which  are  made  of  -|,  -f^,  -£%,  and  ^  the  original 
strength  by  simple  dilution  with  distilled  water. 

Strong  Standard  Solution  of  Indigo. — This  should  be  made  from 
pure  sublimed  indigotin,  2  gm.  of  which,  digested  with  about 
10  gm.  of  fuming  sulphuric  acid  for  some  hours,  diluted  to  about  a 
liter  and  filtered,  will  give  a  solution  of  approximate  strength. 
When  actually  adjusted  so  as  to  agree  with  the  centinormal  nitre 
solution,  4  per  cent,  by  volume  of  oil  of  vitriol,  or  about  that 
proportion,  should  be  contained  in  it ;  this  prevents  alteration  by 
keeping. 

Weak  Standard  Indigo. — This  is  made  to  agree  with  the  J 
standard  nitre  solution  by  actual  experiment,  as  described  further 
on,  and  should  also  contain  4  per  cent,  of  its  volume  of  H2S04. 

In  making  these  solutions  of  indigo  the  so-called  indigo-carmine 
has  often  been  used  (sodic  sulphindylate),  but  this  compound 
generally  gives  more  red  colour  when  oxidized  by  nitric  acid  than 
pure  indigotin;  nevertheless,  there  are  some  specimens  of  indigo- 
carmine  which  are  quite  available  for  the  purpose. 

A  burette  divided  into  -^  c.c.  should  be  used  for  the  indigo,  but 
owing  to  the  deep  colour  of  the  solution  the  reading  is  difficult. 
This  may  be  considerably  lessened  by  rubbing  with  the  finger  some 
white  lead  or  chalk,  mixed  with  oil  or  varnish,  over  the  outside  of 
the  burette,  then  wiping  the  outside  of  the  instrument  clean,  so  as 
to  leave  the  graduations  and  figures  filled  with  white.  In  the  case 
of  using  an  Erdmann's  float,  if  the  ring  is  deeply  cut,  and  filled 
with  white  material,  as  also  the  graduations  of  the  burette,  a 
remarkably  sharp  reading  may  be  obtained  in  the  case  of  all  opaque 
or  highly  coloured  liquids. 

In  water  analysis  it  is  most  convenient  to  work  with  20  c.c.  of 
the  water ;  when  this  is  done  it  is  necessary  to  standardize  the 
indigo  with  20  c.c.  of  the  -|,  y1^-,  -£%,  and  -^  nitre  solutions.  If 
10  c.c.  of  water  are  to  be  employed,  the  indigo  must  be  also 
standardized  with  10  c.c.  of  the  J  and  -J-  nitre  solutions.  It  is 
most  useful  to  standardize  both  for  10  c.c.  and  20  c.c.  of  water,  as 
waters  of  a  greater  range  of  strength  can  then  be  titrated  without 
dilution.  It  is  unnecessary  to  standardize  with  10  c.c.  of  the 
weaker  nitre  solutions ;  if  the  amount  of  nitrate  in  a  water  is  no 
greater  than  that  in  the  -J  nitre  solution,  20  c.c.  of  the  water  may 
be  at  once  taken  for  analysis. 

A  large  supply  of  pure  oil  of  vitriol  will  be  required  for  extensive 
water  analysis.  It  should  be  colourless,  quite  free  from  nitrous 
compounds,  and  contain  as  little  as  possible  of  sulphurous  acid, 
and  must  be  of  nearly  full  gravity.  The  oil  of  vitriol  is  measured 
for  use  in  a  tolerably  wide  burette  provided  with  a  glass  stop-cock. 
A  test-tube  with  foot,  marked  at  each  2  c.c.  from  10  to  40  c.c., 


§    67.  NITRATES.  241 

answers  very  well  for  the  oil  of  vitriol  and  dispenses  with  the 
burette ;  the  oil  of  vitriol  is  then  kept  in  a  stoppered  bottle. 

A  further  requisite  is  a  chloride  of  calcium  bath,  provided  with 
a  thermometer ;  the  bath  is  conveniently  made  in  a  porcelain  basin. 
The  temperature  to  be  maintained  is  140°  C.  As  the  temperature 
keeps  rising  from  the  evaporation  of  the  solution,  it  is  necessary  to 
bring  it  down  to  the  required  point  by  the  addition  of  a  little 
water,  or  calcium  solution,  immediately  before  each  experiment. 
The  bath  is  not  required  when  strong  solutions  of  nitrate  are 
analyzed  by  the  stronger  solution  of  indigo,  the  reaction  in  such 
cases  being  almost  immediate.  With  weak  solutions  of  indigo  and 
nitrate  the  reaction  may  take  some  time,  in  extreme  cases  as  much 
as  five  minutes,  and  it  becomes  essential  for  accuracy  that  the 
temperature  should  be  maintained  throughout  at  the  normal  point. 

The  standardizing  of  the  indigo  solution  is  performed  as  follows : — 

10  c.c.  or  20  c.c.  of  the  standard  nitre  solution  are  placed  in  a  wide- 
mouthed  flask  of  about  150  c.c.  capacity,  as  much  indigo  solution  is  measured 
in  as  is  judged  sufficient,  and  the  whole  mixed.  Oil  of  vitriol  is  next  run 
from  the  burette  into  a  test-tube,  in  quantity  exactly  equal  to  the  united 
volumes  of  the  nitrate  solution  and  indigo.  The  contents  of  the  test-tube  are 
then  poured  as  suddenly  as  possible  into  the  solution  in  the  flask,  the  whole 
rapidly  mixed,  and  the  flask  at  once  transferred  to  the  chloride  of  calcium 
bath.  It  is  essential  for  concordant  results  that  the  oil  of  vitriol  should  be 
uniformly  mixed  with  the  solution  as  quickly  as  possible.  This  is  especially 
necessary  in  the  case  of  strong  solutions  of  nitrate  in  which  the  action  begins 
immediately  after  the  addition  of  the  sulphuric  acid ;  with  such  solutions  it 
is  more  difficult  to  get  duplicate  experiments  to  agree  than  with  weaker 
solutions  in  which  the  action  does  not  begin  at  once,  and  in  which  therefore 
time  is  afforded  for  mixing.  The  operator  should  not  attempt  to  drain  the 
test-tube ;  the  oil  of  vitriol  adhering  to  the  tube  is  a  fairly  constant  quantity, 
and  after  the  first  experiment  the  tube  will  deliver  the  quantity  measured 
into  it. 

It  is  well  to  have  the  flask  covered  by  a  watch-glass  while  holding  it  in 
the  bath.  The  progress  of  the  reaction  should  be  watched,  and  as  soon  as 
the  greater  part  of  the  indigo  has  been  oxidized,  the  contents  of  the  flask 
should  he  gently  rotated  for  a  moment.  With  very  weak  solutions  of  pure 
nitre  no  change  is  observed  for  some  time,  and  it  may  be  necessary  in  some 
cases  to  keep  the  flask  in  the  bath  for  five  minutes.  If  the  colour  of  the 
indigo  is  suddenly  discharged,  it  is  a  sign  that  the  nitric  acid  is  in  considerable 
excess,  and  that  a  considerably  larger  amount  of  indigo  must  be  taken  for  the 
next  experiment.  If  some  of  the  indigo  remains  unoxidized,  a  little 
experience  will  enable  the  operator  to  judge  its  probable  amount,  and  so 
decide  on  the  quantity  of  indigo  suitable  for  the  next  experiment. 

The  amount  of  indigo  which  corresponds  to  the  solution  of  nitrate  is 
found  by  a  series  of  approximating  experiments  made  as  just  described  with 
varying  quantities  of  indigo,  the  oil  of  vitriol  used  being  always  equal  in  volume 
to  the  united  volumes  of  the  nitrate  solution  and  indigo.  The  determination 
is  finished  when  a  quantity  of  indigo  is  left  unoxidized  not  exceeding  O'l  c.c. 
of  the  indigo  solution  used ;  this  amount  can  be  readily  estimated  by  the 
eye.  It  is  well,  until  considerable  experience  has  been  gained,  to  check  the 
result  by  making  a  further  experiment  with  O'l  c.c.  less  indigo,  when  the 
colour  should  be  entirely  discharged.  The  tint  produced  by  a  small  excess 
of  indigo  is  test  seen  by  filling  up  the  flask  with  water.  The  estimated 
excess  of  indigo  is  of  course  deducted  from  the  reading  of  the  burette. 

R 


242 


VOLUMETRIC   ANALYSIS. 


§    67. 


To  reduce  the  number  of  experiments  required  to  obtain  the 
result  it  is  well  to  proceed  with  some  boldness,  and  ascertain  as 
soon  as  possible  what  are  the  limits  between  which  the  quantity  of 
indigo  must  fall.  Seven  experiments  will  be  a  maximum  rarely 
exceeded;  four  experiments  is  about  the  average  required  where 
the  history  of  the  waters  examined  is  already  known. 

When  the  indigo  solution  has  been  standardized  with  the  series 
of  nitre  solutions  already  mentioned,  it  will  be  found  that  the 
quantity  of  indigo  consumed  is  not  strictly  in  proportion  to  the 
nitric  acid  present,  but  diminishes  as  the  nitrate  solution  becomes 
more  dilute.  In  round  numbers,  a  diminution  of  the  amount  of 
nitre  present  to  -§-  is  accompanied  by  diminution  of  the  indigo 
oxidized  to  ^5-;  or,  in  other  words,  if  20  c.c.  of  the  J  standard 
solution  of  nitre  require  10  c.c.  of  indigo,  20  c.c.  of  the  —  nitre 
solution  will  require  only  1  c.c.  of  indigo.  This  is  a  very  important 
fact,  and  necessitates  the  standardizing  of  the  indigo  with  solutions 
of  graduated  strength,  so  that  the  value  of  the  indigo  may  be 
known  for  all  parts  of  its  scale. 

In  consequence  it  becomes  necessary  to  form  a  table  of  the  value 
in  nitrogen  corresponding  to  each  part  of  the  indigo  scale,  and  by 
the  help  of  this  table  every  analysis  subsequently  made  is  calcu- 
lated. Below  is  given  an  ideal  table  of  this  description.  It  is 
assumed,  which  is  very  near  the  truth,  that  a  diminution  to  one- 
eighth  in  the  strength  of  the  nitrate  solution  is  accompanied  by  a 
diminution  to  one-tenth  in  the  indigo  consumed.  It  is  further 
assumed,  which  is  also  near  the  truth,  that  the  alteration  in  the 
relation  of  the  indigo  to  the  nitrate  proceeds  at  a  uniform  rate 
between  the  limits  actually  determined.  The  following  will  be  the 
results  arrived  at  when  using  20  c.c.  of  the  nitrate  solution  for 
each  experiment : — 


Value    of  the    Indigo    in    Nitrogen    for    different    strengths    of 
Nitre    Solution. 


Difference  in 

Strength,  of 
nitre  solution 
used. 

Indigo 
required. 

Difference 
between 
amounts 
of  indigo. 

Nitrogen 
corresponding 
to  1  c.c.  of 
Indigo. 

Difference 
between  the 
nitrogen 
values. 

the  nitrogen 
values  fora 
difference  of 
1  c.c.  in  the 
amount  of 

indigo. 

c.c. 

c.c. 

gram. 

grain. 

gram. 

ff\  Standard 

10-00 

— 

0-000035000 

A      „       .- 

871 

1-29 

0-000035161 

0-000000161 

0-000000125 

A     „      .- 

7-43 

1-28 

0-000035330 

0-000000169 

0-000000132 

'A 

6'14 

•29 

0-000035627 

0-000000298 

0-000000231 

&     „      ... 

4-86 

•28 

0-000036008 

0-000000381 

0-000000298 

A 

3-57 

•29 

0'000036764 

0-000000756 

0-000000586 

A 

2'29 

•28 

0-000038209 

0-000001445 

0-000001129 

A      ,      - 

TOO 

•29 

0-000043750 

0-000005541 

0-000004295 

§  67.  NITKATES.  243 

The  mode  of  using  this  table  is  very  simple.  Supposing  that 
20  c.c.  of  a  water  have  required  5 '3 6  c.c.  of  indigo,  this  amount  is 
seen  to  be  0'5  c.c.  above  the  nearest  point  (4 '86  c.c.)  given  in  the 
table.  We  learn  from  the  right-hand  column  that  0 '000000 149 
must  consequently  be  subtracted  from  the  unit  value  in  nitrogen 
(0-000036008  gm.)  belonging  to  4'86  c.c.  of  indigo.  We  thus  find 
that  the  5'36  c.c.  of  indigo  should  be  reckoned  at  0*000035859  gm. 
of  N  per  c.c.  :  the  water  therefore  contains  9 '6  parts  of  N  as  nitric 
acid  per  million.  If  20  c.c.  of  the  water  have  required  less  than 
1  c.c.  of  indigo,  the  unit-value  corresponding  to  1  c.c.  of  indigo  is 
employed  for  calculating  the  result.  This  will  give  accurate  results 
if  the  oil  of  vitriol  employed  is  quite  pure. 

It  is  not  necessary  in  practice  to  form  so  complete  a  table  as  that 
now  given;  it  will  suffice  to  determine  the  indigo  with  nitre 
solutions  of  •§-,  Y^-,  -^2,  and  ~  strength  :  if  another  solution  is  used, 
that  of  F3T  strength  seems  the  most  important.  It  may  be  sufficient, 
even,  in  some  cases,  simply  to  determine  the  indigo  with  the  ^  and 
e^-  nitre  solutions,  and  to  find  all  the  intermediate  values  by 
calculation ;  examples  will  be  presently  given  showing  the  amount 
of  agreement  between  such  calculation  and  experiment.  If  10  c.c. 
of  water  are  to  be  employed  as  well  as  20  c.c.,  separate  tables 
should  be  formed  giving  the  values  of  the  indigo  in  each  case. 

There  is  one  important  advantage  that  follows  from  this  trouble- 
some necessity  of  standardizing  the  indigo  with  various  nitrate 
solutions ;  it  tends  to  remove  the  errors  due  to  impurities  in  the 
oil  of  vitriol.  As  the  volume  of  the  oil  of  vitriol  used  depends 
far  more  on  the  volume  of  water  taken  than  on  the  quantity  of 
nitric  acid  it  contains,  all  errors  due  to  oxidizing  or  reducing  matter 
contained  in  the  oil  of  vitriol  fall  far  more  heavily  on  determinations 
of  small  quantities  of  nitric  acid  than  on  larger.  Unless,  therefore, 
the  oil  of  vitriol  used  was  absolutely  pure,  it  would  always  be 
necessary  to  standardize  the  indigo  as  now  recommended,  even 
if  the  relation  of  indigo  to  nitric  acid  were  exactly  the  same 
in  weak  and  strong  solutions.  By  standardizing  as  now  described, 
the  errors  due  to  the  sulphuric  acid  affect  the  figures  of  the  table, 
but  not  the  result  of  the  analysis.  Such  standardizing  has  also 
the  effect,  as  far  as  it  goes,  of  calibrating  the  burette,  any 
inequalities  of  capacity  falling  011  the  table,  and  not  on  the 
analyses  calculated  from  it. 

In  standardizing  the  indigo  solution,  and  in  the  subsequent 
experiments  with  it,  some  regard  must  be  paid  to  the  initial 
temperature  of  the  solutions.  A  rise  in  the  initial  temperature 
will  be  attended  by  a  diminution  in  the  quantity  of  indigo 
oxidized;  this  is  most  perceptible  in  the  case  of  the  stronger 
solutions  of  nitrate.  The  following  table  shows  the  results 
obtained  by  standardizing  the  same  indigo  solution  at  two 
temperatures,  representing  nearly  the  extreme  limits  at  which 
the  solution  would  be  used  in  practice.  The  temperature  of  the 

R  2 


244 


VOLUMETRIC   ANALYSIS. 


§  67. 


room  during  the  experiment  Avas  10° ;  for  the  trials  at  the  higher 
temperature,  the  flask  containing  the  indigo  and  nitrate,  and  the- 
test-tube  containing  the  oil  of  vitriol,  were  placed  for  some  time- 
in  a  water  bath  at  22 — 23°  previously  to  being  mixed. 

Indigo    Solution    Standardized    with    10    c.c.    of   Nitre    Solution. 


Strength 
of  nitre 
solution. 

At  10°. 

At  22°. 

Indigo 
required 
(actual) 

Indigo 
calculated 
from  two 
extremes. 

Indigo 
required 
(actual). 

Indigo 

calculated 
from  two 
extremes. 

i  Standard 

*       „       ..- 

TV        „          -. 

A-    „      - 

c.c. 
10-28 
4-97 
2-30 
0-99* 

c.c. 
10-28 
4-97 
232 
0-99 

c.c. 
9-76 
4-78 
2-18 
0-96 

c.c. 
9-76 
4-73 
2-22 
0-96 

Standardized    with    20    c.c.    of   Nitre    Solution. 


i  Standard 

10-26 

10-26 

9-74 

9'74 

*  ::  ::: 

4-84 
2-21 

4-96 
2-31 

4-65 
2-21 

4-74 
2-24 

T5T        jj 

0-99 

0-99 

0-99 

0-99 

It  is  seen  that  a  rise  of  12°  in  temperature  diminishes  the  indigo 
consumed  by  about  5  per  cent,  in  the  case  of  the  stronger  solutions- 
of  nitrate ;  it  is  evident,  therefore,  that  the  indigo  solution  should 
be  standardized  at  nearly  the  same  temperature  at  which  it  is  to  b& 
iised. 

In  the  table  the  quantity  of  indigo  corresponding  to  the- 
intermediate  strengths  of  nitre  solution  has  been  calculated  from 
the  determinations  made  with  the  two  extreme  strengths,  to  show 
the  amount  of  accuracy  to  be  attained  by  this  plan ;  the  agreement 
of  calculation  with  the  results  actually  obtained  is  sometimes  very 
close,  but  in  others  the  difference  is  somewhat  greater  than  the 
errors  of  experiment. 

If  the  indigo  solution  has  been  standardized  with  20  c.c.  of  the 
nitre  solutions  recommended,  the  operator  will  be  able  to  titrate 
waters  containing  nitric  acid  up  to  17 '5  parts  of  nitrogen  per 
million.  If  the  indigo  has  also  been  standardized  with  10  c.c.  of 
the  \  and  J-  nitre  solutions,  the  operator  can,  by  employing  10  c.c. 
of  the  water,  extend  his  range  of  analysis  to  waters  containing 
34  parts  of  nitrogen  per  million.  "Waters  stronger  than  this  should 
be  diluted  for  analysis.  The  natural  error  of  the  determination, 

*  It  must  not  be  supposed  that  it  was  possible  to  work  to  one-hundredth  of  a  cubic 
centimeter ;  in  all  the  figures  given,  the  errors  shown  by  calibrating  the  measuring 
vessels  employed  have  been  taken  account  of,  and  minute  fractions  thus  introduced. 


§    67.  NITRATES.  245 

shown  by  the  performance  of  duplicate  experiments,  will  not 
exceed  1  per  cent,  of  the  nitric  acid  present  in  the  case  of  waters 
containing  17  of  nitrogen  per  million,  but  may  amount  to 
5  per  cent,  with  waters  containing  as  little  as  2  of  nitrogen 
per  million. 

Chlorides  are  of  course  generally  present  in  waters  containing 
nitrates  ;  they  are  not  altogether  without  effect  on  the  determination 
with  indigo. 

The  presence  of  an  abundance  of  chlorides  occasioned  an  error  of 
deficiency  of  about  1  '5  per  cent,  in  the  case  of  a  |-  standard  solution 
of  nitre,  and  an  error  of  excess  of  4*4  per  cent,  in  the  case  of  a 
solution  of  one-quarter  this  strength.  At  some  point  between  the 
two  the  error  was  probably  nil.  The  different  direction  of  the 
error  is  apparently  due  to  the  effect  of  chlorides  on  the  duration  of 
the  reaction.  As  nitre  solutions  become  weaker  the  time  occupied 
by  the  reaction  with  indigo  is  lengthened,  and  the  proportion  of 
indigo  consumed  diminished.  In  the  presence  of  chlorides  the 
duration  of  the  reaction  in  weak  solutions  is  much  shortened,  and 
the  quantity  of  indigo  consumed  is  consequently  increased. 

The  error  introduced  by  chlorides  is  for  many  purposes  insignifi- 
cant. Thus,  two  nitre  solutions  employed  contained  17 '8  and  4 '3 
of  nitrogen  per  million ;  titrated  in  the  presence  of  excess  of 
chloride  they  yielded  17*5  and  4*5  per  million.  As  in  water 
analysis  the  amount  of  chlorine  is  always  determined,  it  would  be 
well  to  make  this  part  of  the  analysis  preliminary  to  the  nitric  acid 
determination.  The  indigo  might  also  be  standardized  with  nitre 
solutions  containing  excess  of  chloride,  and  a  small  quantity  of 
pure  chloride  added  to  all  waters  deficient  in  this  constituent. 
Finkener  has  already  recommended  the  addition  of  chlorides  to 
the  standard  nitre  solutions. 

Nitrites  are  unfortunately  not  capable  of  being  determined  by 
indigo ;  the  amount  of  indigo  oxidized  is  much  less  than  in  the 
case  of  nitrates,  and  the  reaction  is  far  from  being  sharp. 

Nitrites  may  be  easily  converted  into  nitrates  by  treatment  with 
permanganate,  and  may  then  be  determined  by  indigo.  A  solution 
of  commercial  potassic  nitrite,  which  contained  by  the  Crum- 
Frankland  method  31*5  parts  of  nitrogen  per  million,  gave  only 
22 '1  parts  of  nitrogen  when  tested  by  indigo  previously  standardized 
with  a  nitrate.  The  same  quantity  of  nitrite,  in  a  more  concen- 
trated form,  was  first  treated  with  permanganate,  to  remove  any 
accidental  reducing  matter,  then  acidified  with  sulphuric  acid, 
and  permanganate  slowly  added  till  decolorization  no  longer 
occurred.  The  solution  was  finally  brought  to  the  same  volume  as 
in  the  first  experiment,  and  tested  with  indigo ;  it  now  yielded 
32 '4  parts  of  nitrogen  per  million. 

If  chlorides  are  present  as  well  as  nitrites,  free  chlorine  may  be 
produced  during  treatment  with  permanganate,  and  the  determina- 
tion with  indigo  consequently  come  out  too  high ;  in  this  case  it 


246  VOLUMETRIC   ANALYSIS.  §    67. 

may  be  well  to  make  the  liquid  slightly  ammoniacal  after  the 
treatment  with  permanganate,  and  raise  the  temperature  for  an 
instant  to  boiling.  This  mode  of  proceeding,  according  to 
Boussingault,  completely  removes  free  chlorine. 

The  weakest  point  in  the  indigo  method  is  its  behaviour  in  the 
presence  of  organic  matter.  Warington  found  that  a  small 
quantity  of  cane-sugar  greatly  reduced  the  quantity  of  indigo 
oxidized  by  a  nitrate,  the  effect  of  the  sugar  being  greater  in  dilute 
solutions,  in  which  the  reaction  was  naturally  more  prolonged. 
The  use  of  a  large  proportion  of  oil  of  vitriol  also  increased  the 
effect  of  the  sugar.  Carbolic  acid  and  urea  also  act  as  reducing 
agents,  while  tartaric  acid  has  been  proved  by  many  experiments  to 
be  without  effect. 

The  indigo  method  cannot  be  employed  with  safety  for  the 
analysis  of  waters  distinctly  contaminated  with  organic  matter. 
There  appears  to  be  no  method  of  determining  small  quantities  of 
nitric  acid,  save  that  of  Sch  losing,  which  is  free  from  suspicion 
under  these  circumstances. 

In  the  case  of  ordinary  drainage  waters  the  agreement  between 
the  indigo  method  and  that  of  Cr  urn-Frank  land  is  very  good. 
The  following  analyses  of  drainage  waters  refer  to  waters  collected 
from  unmanured  arable  land  (Warington).  The  figures  represent 
nitrogen  per  million  : — 

Crum-Frankland  method.  Indigo  method. 
22'7  23'0 

16-6  16-9 

13'3  13-8 

In  a  series  of  comparative  analyses,  by  the  same  two  methods, 
of  nitrified  solutions  of  ammonic  chloride  (/.  C.  S.  1879,  448) 
the  agreement  between  the  results  was  generally  good,  and  the 
comparisons  instituted  by  Hatton  (/.  C.  S.  1881,  258)  are  equally 
satisfactory. 

The  general  conclusion  respecting  the  indigo  method  for  deter- 
mining nitric  acid  will  be,  that  it  is  excellently  adapted  by  its 
simplicity,  rapidity,  and  delicacy  for  general  use  in  water  analysis ; 
but  that  accuracy  can  be  secured  only  by  working  under  the  same 
conditions  which  obtained  when  the  indigo  was  standardized. 
In  the  presence  of  organic  matter  the  results  obtained  with  indigo 
must  be  accepted  as  probably  below  the  truth. 

The  above  description  is  given  mainly  in  Warington's  own 
words,  and  is  undoubtedly  the  best  plan  of  working  the  process  so 
as  to  secure  accuracy;  notwithstanding  this,  there  are  some 
operators  who  seem  disposed  to  discard  it  even  for  water  analysis 
(Dupre,  Analyst,  vi.  39).  I  am  inclined  to  think  that  the 
apparent  or  alleged  inaccuracies  arise  from  want  of  patience  or 
practice,  and  that  if  the  manipulations  are  well  understood,  the 
process  will  give  as  good  average  results  as  most  of  the  processes  in 
use  for  the  determination  of  small  quantities  of  nitric  acid. 


§    67.  NITRATES.  247 

It  is  certainly  the  most  handy  process  for  rapidly  ascertaining 
the  approximate  amount  of  nitric  acid  in  any  given  substance ;  and 
as  an  adjunct  to  the  use  of  some  other  methods,  where  it  is 
necessary  to  know  as  nearly  as  possible  the  amount  of  nitric  acid 
to  be  dealt  with,  it  is  without  a  rival.  For  such  purposes  in  the 
case  of  materials  such  as  guanos,  manures,  etc.,  the  process  may  be 
shortened  as  follows  : — 

(1)  A  rough  test  is  made  with  10  c.c.  of  the  nitrate  solution  and  stronger 
indigo  using  20  c.c.  of  oil  of  vitriol. 

(2)  If  10  c.c.  of  the  nitrate  solution  require  less  than  1  c.c.  of  stronger 
indigo,  then  10  c.c.  of  it  may  at  once  be  titrated  with  the  weaker  indigo ; 
the  volume  of  acid  being  regulated  by  the  first  experiment  to  equal  the 
volume  of  nitrate  solution,  plus  the  volume  of  weaker  indigo  required.     1  c.c. 
or  so  of  acid  either  way  does  not  influence  the  experiment.     This  second 
titration,  if  carefully  performed,  using  an  ordinary  spirit  lamp  of  small  flame 
for  heating,  will  give  the  value  of  the  nitrate  in  terms  of  weak  indigo. 

(3)  If  in  the  preliminary  test  10  c.c.  of  the  nitrate  solution  require  more 
than  1  c.c.,  but  less  than  3  c.c.  of  stronger  indigo,  the  solution  may  be 
titrated  at  once  with  stronger  indigo,  using  about  12  c.c.  of  acid. 

(4)  If  in  the  preliminary  test  10  c.c.  of  nitrate  solution  require  more 
than  4  c.c.  of  stronger  indigo,  the  solution  must  be  diluted  twice,  thrice,  or 
more  as  the  case  may  be,  so  as  to  bring  it  to  about  the  strength  of  the  weaker 
standard  nitre  solution,  when  it  may  be  finally  titrated  with  the  stronger 
indigo  and  the  correct  amount  of  acid. 


7.     G-asometric   estimation   as   Nitric   Oxide. 

This  method  of  estimating  nitrogen  existing  as  nitric  and  nitrous 
acids,  either  separately  or  together,  is  an  exceedingly  delicate  one, 
and  capable  of  great  accuracy  under  proper  manipulation. 

It  is  now  best  known  as  the  Crum -Frank land  method,  the 
original  idea  emanating  from  Crum,  and  afterwards  improved  in 
detail  of  manipulation  by  Frank  land  and  Armstrong,  in  their 
well-known  method  of  water  analysis. 

So  far  as  the  use  of  the  method  for  water  analysis  is  concerned, 
the  process  is  given  in  Part  VI.,  where  the  shaking  tube  which  is 
used  for  the  decomposition  of  the  nitrogen  compounds  by  mercury 
and  sulphuric  acid  is  figured,  and  the  details  of  the  process  as 
applied  to  waters  fully  described. 

The  method  there  given,  however,  requires  the  use  of  a  gas 
apparatus.  This  method  obviates  that  necessity,  and  though  the 
results  cannot  be  said  to  be  absolutely  as  exact,  they  are  very 
satisfactory  for  some  purposes,  such  as  the  examination  of  nitrous 
vitriol,  raw  commercial  nitrates,  manures,  etc. 

The  apparatus  used  is  Lunge's  nitrometer,  a  figure  of  which  is 
given  in  the  section  on  technical  gas  analysis,  accompanied  with 
a  description  of  the  method  of  using  it.  The  application  of  the 
instrument  to  the  estimation  of  nitrous  and  nitric  acids  in  vitriol 
and  other  substances  is  explained  in  the  same  section. 

The  volume  of  the  nitric  oxide  obtained  can  be  read  off  to  -^  c.c. ; 


248  VOLUMETRIC   ANALYSIS.  §.   67. 

it  is  reduced  by  Bunsen's  tables  to  0°  and  760  m.m.,  and  the 
percentage  of  the  acid  calculated  from  it.  Each  c.c.  of  NO, 
measured  at  0°  and  760  m.m.,  corresponds  to  1*343  m.gm.  NO,  or 
1-701  m.gm.  N203,  or  2417  m.gm.  N205,  or  4'521  KNO3,  or 
3 '805  m.gm  NaNO3.  By  this  process,  of  course,  nitric  and  nitrous 
acids  cannot  be  distinguished,  but  are  always  estimated  together. 

The  principle  of  the  reaction  is  explained  in  the  section  on  Water 
Analysis  (Estimation  of  Nitrates  and  Nitrites),  and  the  satisfactory 
nature  of  the  method  for  vitriol-testing  has  been  amply  demonstrated 
by  Watts,  by  Davis  (C.  N.  xxxvii.  45),  and  many  others.  The 
instrument  itself  has  been  made  in  several  modified  ways,  but  the 
principle  of  its  construction  is  the  same. 

Allen  (Analyst,  v.  181)  recommends  the  use  of  this  instrument 
for  the  estimation  of  nitrates  and  nitrites  in  water  residues ;  and 
to  obviate  the  difficulty  in  reading  the  volume  which  sometimes 
arises  from  the  mercurial  froth,  he  uses  two  nitrometers  side  by 
side,  in  one  of  which  is  worked  a  pure  standard  nitrate  solution,  and 
in  the  other  the  material  for  analysis  under  precisely  the  same 
conditions  of  temperature,  pressure,  etc.  If  the  apparatus  contain- 
ing the  comparative  test  is  free  from  leakage,  it  may  be  retained  for 
a  long  period  for  the  purpose  of  comparison. 

8.      Colorimetric    Methods. 

Phenol  Method. — Both  this  and  the  carbazol  method  are 
applicable  chiefly  to  waters  where  only  small  proportions  of  nitric 
acid  are  to  be  estimated.  The  solutions  required  are — 

Standard  Potassic  nitrate. — 0'7215  gm.  of  KNO3  is  dissolved 
in  a  liter  of  water.  1  c.c.  of  this  solution  =  -^  m.gm.  of  N,  or  one 
part  N  in  100,000.  100  c.c.  of  it  should  be  diluted  to  a  liter  for 
use  in  the  actual  analysis,  and  10  c.c.  taken,  to  avoid  the  possible 
error  resulting  from  measuring  only  1  c.c. 

Phenol  Sulphuric  acid. — 80  c.c.  of  liquified  pure  phenol  is 
poured  into  200  c.c.  of  pure  concentrated  sulphuric  acid  in  a  flask, 
and  kept  on  a  boiling  water  bath  for  eight  hours.  The  mixture  is 
cooled,  and  140  c.c.  of  pure  hydrochloric  acid  with  420  c.c.  of 
water  added.  The  solution  is  then  ready  for  use. 

The  Analysis :  10  c.c.  of  the  water  under  examination  and  10  c.c.  of  the 
standard  potassic  nitrate  are  pipetted  into  two  small  beakers  and  placed  near 
the  edge  of  a  hot  plate.  When  nearly  evaporated  they  are  removed  to  the 
top  of  the  water-oven  and  left  there  till  they  are  evaporated  to  complete 
dryness.  As  this  operation  usually  takes  about  an  hour  and  a  half,  it  is 
better,  when  time  is  an  object,  to  evaporate  to  dryness  in  a  platinum  dish  over 
steam.  The  residue  in  each  case  is  then  treated  with  1  c.c.  of  the  phenol- 
sulphuric  acid,  and  the  beakers  are  placed  on  the  top  of  the  water-oven.  If 
the  water  under  examination  contain  a  large  quantity  of  nitrates  the  liquid 
speedily  assumes  a  red  colour,  which,  in  a  good  water,  will  not  appear  for 
about  ten  minutes.  After  standing  for  fifteen  minutes  the  beakers  are 
removed,  the  contents  of  each  washed  out  successively  into  a  100  c.c. 
measuring  glass,  a  slight  excess  (about  20  c.c.  of  0'96)  of  ammonia  added, 


§  67.  NITRATES.  249 

the  100  c.c.  made  up  by  the  addition  of  water,  and  the  yellow  liquid 
transferred  toaNessler  glass.  The  more  strongly  coloured  liquid  is  then 
partly  transferred  to  the  measuring  glass  again  and  the  tints  compared 
a  second  time.  In  this  way  the  tints  are  adjusted,  and  when,  as  far  as 
possible,  matched,  the  liquid  that  has  been  partially  removed  is  made  up  to 
the  100  c.c.  mark  with  water,  and,  after  well  mixing,  finally  compared.  If 
not  exactly  the  same,  a  new  liquid  can  at  once  be  made  up,  probably  of 
exactly  the  same  tint,  as  the  first  experiment  gives  very  nearly  the  number 
of  c.c.  of  the  one  equivalent  to  the  100  c.c.  of  the  other.  A.  E.  Johnson 
in  his  very  useful  Analyst's  Laboratory  Companion  (p.  50)  has  given  a 
table  for  obtaining  the  nitrogen  in  parts  per  100,000,  and  also  in  grains  per 
gallon,  by  this  method. 

In  the  case  of  very  good  waters,  20,  50,  or  more  c.c.  should  be  evaporated 
to  a  small  bulk,  rinsed  into  a  small  bsaker,  and  evaporated  to  dryness  and 
treated  as  above — only  5  c.c.  of  the  standard  potassic  nitrate  (  =  0'5  N  in 
100,000)  being  taken.  In  the  case  of  very  bad  waters,  10  c.c.  should  be 
pipetted  into  a  100  c.c.  measuring  flask  and  made  up  to  the  mark  with 
distilled  water,  then  10  c.c.  of  the  well  mixed  liquid  (  =  1  c.c.  original  water) 
withdrawn  and  treated  as  above. 

The  Carbazol  Method. — The  standard  potassic  nitrate  and  pure 
sulphuric  acid,  as  above,  are  required  as  well  as  the  following  special 
reagents : — 

(a)  Silver  sulphate   solution  containing  4*3945  gm.  per  liter ; 
1    c.c.  will   precipitate  one  part   of   chlorine   per    100,000   from 
100  c.c.  of  water. 

(b)  Aluminium  sulphate  solution  free  from  chlorides  and  iron, 
5  gm.  per  liter. 

(c)  Carbazol  Solution. — 0*6  gm.  carbazol  is  dissolved  in  glacial 
acetic  acid,  and  the  solution  made  up  to  100  c.c.  with  the  glacial 
acid.     For  use,  1  c.c.  of  this  solution  is  withdrawn  by  a  pipette 
and  mixed  with  15  c.c.  of  pure  re-distilled  sulphuric  acid. 

It  is  advisable  to  prepare  a  series  of  solutions  containing  0*03, 
0-05,  0-07,  etc.,  parts  of  nitrogen  per  100,000  from  the  standard 
nitrate  solution  by  diluting  with  water. 

The  Analysis  :  To  100  c.c.  of  the  water,  the  amount  of  chlorides  in  which 
has  first  been  ascertained,  sufficient  of  the  silver  sulphate  solution  is  added 
from  a  burette  to  precipitate  all  the  chlorides.  To  this  solution,  containing 
the  silver  chloride  in  suspension,  2  c.c.  of  the  aluminium  sulphate  solution  is 
added,  and  the  whole  made  up  to  a  convenient  bulk,  110  c.c.  in  the  case  of 
waters  containing  1  to  6  parts  of  chlorine  per  100,000.  The  solution  is  then 
filtered,  and  2  c.c.  of  this  filtrate  are  then  taken  for  the  nitrate  estimation, 
and,  of  course,  the  amount  found  must  be  calculated  from  the  diluted  bulk 
of  the  solution.  To  the  2  c.c.  of  the  filtered  water  contained  in  a  test-tube, 
4  c.c.  concentrated  sulphuric  acid  is  added,  and  the  mixture  well  cooled. 
1  c.c.  of  the  carbazol  solution  in  sulphuric  acid  as  above  described  is  then 
added,  and  a  bright  green  colour  appears  in  a  few  moments  if  nitrates  are 
present.  The  amount  of  nitrate  is  roughly  gauged  from  the  colour 
produced,  and  2  c.c.  of  the  standard  nitrate  solution,  considered  to  be  equal 
to  it,  is  placed  in  a  second  test-tube,  and  the  operation  repeated  with  it  and 
a  fresh  2  c.c  of  the  water  under  examination  at  the  same  time.  If  the 
tints  are  not  similar  a  fresh  comparison  must  be  made,  and  in  every  case  it  is 
necessary  to  repeat  the  operation  with  a  fresh  quantity  of  the  water,  so  that 
the  colours  may  be  developed  as  nearly  as  possible  simultaneously. 

The  author  states  that  O'OOOG  m.gm.  of  nitrogen  as  nitrate  may  be  detected 


250 


VOLUMETRIC  ANALYSIS. 


§    67. 


by  the  carbazol  method.  The  removal  of  chlorides  is  necessary  for  accurate 
results,  but  the  filtration  does  not  take  much  time  when  aluminium  sulphate 
solution  is  added  as  described. 


NITRITES. 
1.     lodometric   method. 

Duns  tan  and  Dymond  (Pliarm.  Journ.  [3]  xix.  741)  have 
devised  a  method  for  the  estimation  of  N20S  in  organic  and 
inorganic  combination  which  is  both  simple  in  operation  and 
accurate  in  results.  The  authors  point  out  that  although  the 
inorganic  nitrites  may  be  accurately  analyzed  by  gasometric  methods, 
or  by  permanganate,  it  is  impossible  to  use 
such  methods  for  the  organic  compounds  or 
their  alcoholic  solutions.  The  reaction  upon 
which  the  method  depends  is  not  new,  being- 
based  on  the  following  equation — 

2HI  +  2HX02  =  2H20  +  2X0  + 12. 

The  liberated  iodine  is  titrated  with  T^  thio- 
sulphate  in  the  usual  way.  The  chief  merit 
in  the  process  is  the  simple  form  of  apparatus 
used,  and  which  is  shewn  in  fig.  41. 

A  stout  glass  flask,  having  a  capacity  of 
about  100  c.c.,  is  closed  by  a  tightly  fitting 
rubber  stopper,  through  which  passes  a  piece  of 
rather  wide  glass  tubing  (C),  one  end  of  which 
(that  within  the  flask)  is  cut  off  obliquely,  so 
that  liquid  may  flow  freely  through  it.  The 
other  end  of  the  tube  is  connected  by  means 
of  a  piece  of  thick  rubber  tubing  with  a 
larger  glass  tube,  which  forms  a  lipped  funnel 
(A).  A  steel  screw  clamp  (B)  regulates  com- 
munication between  the  funnel  and  the  tube, 
and  the  short  interval  of  rubber  which  is  not 
occupied  by  glass  tubing  forms  a  hinge  upon 
which  the  flask  may  be  moved  into  a  position 
at  right  angles  to  the  funnel,  in  order  to  mix 
by  agitation  the  liquids  which  are  introduced 
into  the  apparatus.  The  absence  of  any  leak 
in  the  apparatus  is  ascertained  by  boiling 
about  50  c.c,  of  water  in  the  flask  until  steam 
has  continuously  issued  from  the  funnel  for 
some  few  minutes,  when  the  screw  clip  is 
quickly  closed  and  simultaneously  the  source 
of  heat  is  removed.  A  little  water  is  now 

placed  in  the  funnel  and  the  flask  is  cooled  by  immersion  in  water. 

On  sharply  inverting  the  flask  the  "  click "  of  the  water  against 


§67.  NITRITES.  251 

the  airless  flask  should  be  quite  distinct.  No  water  should  be 
drawn  from  the  funnel  or  from  any  of  the  joints  into  the  flask, 
and  no  diminution  in  the  intensity  of  the  "  click "  should  be 
observed  after  the  apparatus  has  been  standing,  neither  when  the 
flask  is  inverted  and  the  funnel  empty  should  any  bubbles  of  air 
pass  through  into  the  liquid.  Having  thus  proved  the  absence 
of  any  leak  in  the  apparatus  it  is  ready  for  use.  The  flask  is  now 
free  from  all  but  mere  traces  of  oxygen.  A  conclusive  proof  of 
this  is  obtained  by  boiling  in  the  flask  a  solution  of  potassic 
iodide,  acidified  with  diluted  sulphuric  acid,  and  then,  after  the 
closed  flask  has  been  cooled,  the  funnel  removed  and  its  place 
taken  by  a  smaller  glass  tube  filled  with  air-free  water,  the 
apparatus  is  connected  with  a  reservoir  of  pure  nitric  oxide. 
When  the  clamp  is  unscrewed  nitric  oxide  is  drawn  into  the  flask, 
and  should  any  oxygen  be  present  nitrous  acid  will  be  produced, 
and  consequently  iodine  will  be  set  free.  This  experiment  has 
often  been  made  by  the  authors,  who  have  failed  to  observe  any 
but  an  insignificant  trace  of  liberated  iodine, 

The  Analysis :  5  o.c.  of  a  10  per  cent,  solution  of  potassic  iodide,  5  c.c.  of 
a  10  per  cent,  solution  of  sulphuric  acid,  and  40  c.c.  of  water  are  introduced 
into  the  flask,  which  is  securely  fitted  with  the  cork  carrying  the  funnel  and 
tube.  The  screw  clip  being  open,  and  a  free  passage  left  for  the  escape  of 
steam,  the  liquid  is  boiled.  After  a  few  minutes,  when  any  iodine  which 
may  have  been  liberated  has  been  expelled,  and  the  upper  part  of  the  flask  is 
completely  filled  with  steam,  which  is  also  freely  issuing  from  the  funnel,  the 
clip  is  tightly  closed,  and  at  the  same  moment  the  source  of  heat  is  removed. 
A  little  water  is  now  put  into  the  funnel,  and  also  on  the  rim  of  the  flask,  as 
a  safeguard  against  a  possible  minute  leakage,  and  the  vessel  is  cooled  by 
immersion  in  water.  A  solution  containing  a  known  weight  of  the  nitrite 
(equivalent  to  about  O'l  gm.  of  nitrous  acid)  is  placed  in  the  funnel,  and 
slowly  drawn  into  the  flask  by  cautiously  unscrewing  the  clip.  The  liquid 
which  adheres  to  the  funnel  is  washed  into  the  flask  with  recently  boiled  and 
air-free  water,  care  being  taken  that  during  this  operation  no  air  is  admitted 
into  the  flask.  When  experiments  are  being  made  with  organic  nitrites 
which  are  insoluble  in  water,  they  are  dissolved  in  alcohol,  and  alcohol  is  also 
used  to  wash  the  funnel.  When  the  nitrite  is  very  volatile,  a  little  cold 
alcohol  should  be  put  in  the  funnel,  and  the  point  of  the  pipette  containing 
the  nitrite  should  be  held  at  the  bottom  of  the  funnel  beneath  the  alcohol, 
and  the  liquid  quickly  drawn  from  the  pipette  into  the  flask.  The  nitrate 
having  been  introduced,  the  flask  is  well  shaken  and  the  liberated  iodine  is 
titrated  with  a  standard  solution  of  sodic  thiosulphate,  small  quantities  of 
which  are  delivered  from  a  burette  into  the  funnel  and  gradually  drawn  into 
the  flask ;  the  screw  clip  renders  it  quite  easy  to  admit  minute  quantities  of 
the  solution.  As  soon  as  the  iodine  is  decolorized  any  standard  solution 
remaining  in  the  funnel  is  returned  to  the  burette.  Or  the  funnel  may, 
before  the  titration  is  commenced,  be  replaced  by  the  burette  itself,  and  the 
standard  solution  delivered  direct  into  the  flask.  Starch  may  be  used  as  an 
indicator,  but  it  is  usually  quite  easy  to  observe  the  complete  disappearance  of 
the  yellow  colour  of  the  dissolved  iodine.  Erom  the  volume  of  the  standard 
solution  used,  the  amount  of  nitrous  acid  is  calculated  from  the  equation 
before  given. 

It  is  obvious  that  the  apparatus  might  be  improved  in  several 
respects,  as,  for  example,  by  constructing  it  entirely  of  glass,  with 


252  VOLUMETRIC  ANALYSIS.  §    67. 

a  ground  stopper  and  tap,  as  well  as  by  the  use  of  a  graduated 
funnel  to  deliver  the  standard  solution,  and  also  in  other  ways. 

The  authors  quote  numerous  experiments,  comparing  the  method 
with  careful  estimations  of  sodic  and  ethyl  nitrites,  gasometrically 
shewing  excellent  results. 

As  a  further  test  of  the  accuracy  of  the  process,  experiments 
were  made  with  various  organic  nitrites  of  known  purity.  In 
each  instance  a  solution  of  the  nitrite  was  made  by  weight,  and  a 
weighed  quantity  was  used  for  the  estimation.  To  prevent  any 
loss  of  these  volatile  nitrites  the  experiments  were  conducted  in. 
the  following  manner : — A  well-stoppered  bottle  half  filled  with 
the  alcohol  corresponding  to  the  nitrite*  to  be  estimated  was 
weighed.  Sufficient  of  the  nitrite  was  now  introduced  by  means 
of  a  pipette  to  constitute  approximately  a  2  per  cent,  solution,  and 
the  liquid  again  weighed.  The  exact  strength  of  the  solution 
having  been  thus  determined,  the  contents  of  the  bottle  were  well 
mixed,  and  the  neck  and  stopper  of  the  bottle  dried.  The  bottle 
was  now  re-weighed,  and  about  2  c.c.  of  the  solution  removed  by  a 
pipette,  care  being  taken  not  to  wet  the  neck  of  the  bottle.  The 
liquid  having  been  introduced  into  the  flask  without  exposure  to 
air,  in  the  manner  which  has  been  previously  described,  the  bottle 
containing  the  solution  was  again  weighed.  The  results  obtained 
with  ethyl  nitrite  were  : — 

Taken.  Found. 

0'088  gm.  0'089  gm. 

0-176    „  0-179    „ 

0-113    ,.  0-115    ,. 


2.     Analysis   of  Alkaline  Nitrites   by  Permanganate. 

Kinnicutt  and  ISTef  (Amer.  Chem.  Journ,)  have  experimented 
on  the  following  method,  and  obtained  very  fair  results. 

The  sample  of  nitrite  is  dissolved  in  cold  water  in  the  proportion  of  about 
1  to  300 :  to  this  liquid  ^  permanganate  is  added,  drop  by  drop,  till  it  has  a 
permanent  red  colour ;  then  2  or  3  drops  of  dilute  H2SO4,  and  immediately 
afterwards  a  known  excess  of  the  permanganate.  The  liquid,  which  should 
now  be  of  a  dark  red  colour,  is  strongly  acidified  with  pure  H2S04,  heated 
to  boiling,  and  the  excess  of  permanganate  determined  by  means  of  freshly 
prepared  ^  oxalic  acid.  1  c.c.  permanganate  —  0"0345  gm.  NaNO'2,  or 
0-0425  gm.  KNO2. 

Of  course  there  must  be  no  other  reducing  substance  than  the 
nitrite  present  in  the  material  examined,  and,  to  ensure  accuracy, 
a  blank  experiment  should  be  made  with  the  like  proportions  of 
H2S04  and  oxalic  acid. 

*The  corresponding  alcohol  was  employed  to  prevent  loss  consequent  on  the  occurrence 
of  a  reverse  chemical  change,  which  takes  place  when  a  lower  homologous  alcohol  is 
mixed  with  the  nitrite  corresponding  to  a  higher  homologous  alcohol ;  for  example, 
a  solution  of  amyl  nitrite  in  ethyl  alcohol  soon  becomes  a  solution  of  ethyl  nitrite  in 
amyl  alcohol,  from  which  the  ethyl  nitrite  rapidly  volatilizes. 


§67.  NITRITES.  253 

3.     Grasometric   method. 

Percy  Frankland  («/.  C.  S.  liii.  364)  adopts  this  method  for 
the  estimation  of  nitrous  acid  in  small  quantity,  but  too  large  for 
colorimetric  estimation,  and  where  also  ammonia,  organic  matters, 
and  nitrates  may  co-exist.  It  is  based  on  the  fact  that  when 
nitrous  acid,  together  with  excess  of  urea,  is  mixed  with  sulphuric 
acid  in  the  cold,  the  reaction  is 

2CO(^sTH2)2  +  N203  =  CO(ATH40)2  +  CO2  +  2K"2. 

The  decomposition  is  made  in  the  Cr  urn-Frank  land  shaking  tube, 
described  and  figured  in  Part  VI.,  and  the  evolved  nitrogen  gas 
measured  in  the  usual  gas  apparatus.  The  ordinary  nitrometer 
may  also  be  used  for  larger  quantities  of  NO2  by  the  same  method. 
In  the  case  of  an  ordinary  alkali  nitrite,  the  dry  substance,  or 
its  solution  evaporated  to  dryness,  is  mixed  with  excess  of 
crystallized  urea,  and  dissolved  in  about  2  c.c.  of  boiling  water  in 
a  beaker,  then  transferred,  with  the  rinsings,  to  the  cup  of  the 
apparatus,  and  passed  into  the  tube.  A  few  c.c.  of  dilute 
sulphuric  acid  (1:5)  are  then  passed  in.  A  vigorous  evolution  of 
gas  takes  place,  and  continues  for  some  five  minutes ;  the  gas  is  a 
mixture  of  nitrogen  and  carbonic  anhydride.  The  decomposition 
is  complete  in  fifteen  minutes.  A  solution  of  pure  sodic  hydrate 
(1  :  3)  is  now  added  through  the  cup,  and  the  mixture  violently 
shaken,  until  the  CO2  is  absorbed.  The  gas  and  liquid  are  then 
transferred,  by  means  of  another  mercury  trough,  to  the  laboratory 
vessel,  and  the  gas,  which  is  double  the  volume  of  the  N  existing 
as  N203,  measured  in  a  gas  apparatus,  and  its  weight  calculated  in 
the  usual  way. 

Example :  A  solution  of  sodic  nitrite  was  made  and  standardized  with 
permanganate,  the  result  being  that  10  c.c.  =  0*001346  gm.  N.  10  c.c.  of  the 
same  solution  was  evaporated  to  dryness  in  a  small  beaker,  about  0*2  gm.  of 
urea  added,  the  whole  dissolved  in  2  c.c.  of  hot  water,  which,  with  the 
rinsings,  were  transferred  through  the  cup  into  the  tube,  treated  with 
sulphuric  acid  and  caustic  soda,  then  transferred  to  the  gas  apparatus  with 
the  following  results : — Volume  of  N,  13*79  c.c. ;  mercurial  pressure,  127  5 
m.m. ;  temperature,  17*7°  C.  The  weight  of  N  thus  found,  after  the 
necessary  corrections,  was  0*0013645  gm. 

The  Cr  urn-Frank  land  mercury  method,  described  in  the 
section  on  Water  Analysis,  and  in  which  the  same  shaking  tube  is 
used,  does  not  distinguish  between  nitric  and  nitrous  nitrogen; 
but  Percy  Frankland  required  a  method  for  the  estimation  of 
nitrous  acid  in  a  mixture  of  nitrates,  peptones,  sugar,  and  various 
salts  occurring  in  a  solution  used  for  cultivation  of  micro-organisms, 
and  the  experiments  carried  out  by  him  showed  that  when  such  a 
mixture  was  evaporated  to  dryness  the  loss  of  HNO2  was  consider- 
able, and  the  results  came  out  much  too  low.  Further  experiment, 
however,  showed  that  the  addition  of  a  slight  excess  of  caustic 
potash  during  evaporation  prevented  the  loss  of  any  H^O2 ;  and  on 


254  VOLUMETRIC  ANALYSIS.  §    68. 

the  other  hand  the  addition  of  a  slight  excess  of  ammonic  chloride 
entirely  destroyed  it.  Therefore  by  a  combination  of  the  mercury 
and  the  urea  methods,  the  estimation  of  nitric  and  nitrous  acids 
may  be  satisfactorily  accomplished,  the  destruction  of  the  HNO2 
on  the  one  hand  being  effected  by  excess  of  KH4C1,  whilst  on  the 
other  hand  all  loss  of  HNO2  may  be  avoided  by  evaporation  with 
caustic  alkali.  The  mode  of  procedure  has  the  advantage  over  all 
differential  methods,  in  that  each  acid  is  determined  individually 
and  independently  of  the  other. 

4.     Mixtures   of  Alkaline    Sulphites,    Thiosulphates,    and   Nitrites. 

Lunge  and  Smith  (/.  S.  C.  I.  ii.  465)  have  shown  that  the  only 
satisfactory  method  of  completely  oxidizing  sulphites  and  thio- 
sulphates  by  permanganate  is  to  add  to  the  solution  a  large  excess 
of  permanganate,  more  than  sufficient  for  complete  oxidation,  and 
with  formation  of  MnO2.  Excess  of  FeSO4  is  then  added,  and 
again  permanganate  till  pink.  When  such  a  mixture  contains 
nitrites,  they  will  of  course  be  oxidized  to  nitrates. 

To  find  the  amount  of  nitrites  present,  therefore,  the  following 
method  is  adopted  :  — 

The  solution  of  the  substance  in  not  too  large  quantity  is 
exactly  oxidized  as  described,  a  known  volume  of  standard  ferrous 
sulphate  is  added,  together  with  a  large  excess  of  strong  H2S04. 
The  mixture  is  boiled  nearly  to  dryness  in  a  flask  with  slit  valve, 
diluted,  and,  when  cool,  titrated  with  permanganate.  The  difference 
between  the  volume  then  required  and  that  required  by  the  original 
Fe2S04,  represents  the  nitric  acid  which  has  been  reduced  and 
escaped  as  NO. 

The  exceedingly  delicate  colorimetric  method  of  estimating 
nitrites  originally  devised  by  Griess,  and  improved  by  others,  will 
be  described  in  the  section  on  Water  Analysis. 

OXYGEN. 


§68.  THE  volumetric  determination  of  the  dissolved  oxygen  in 
water,  is  an  operation  of  some  importance  in  water  analysis.  It  is 
well  known  that  organic  and  bacterial  contamination  generally 
exist  side  by  side  ;  the  organic  matter  offering  a  suitable  nidus  for 
the  growth  of  bacterial  life.  Water  thus  contaminated  is 
de-oxygenated  by  the  living  organisms,  which  consume  oxygen 
during  their  growth;  hence  the  importance  of  the  estimation  of 
dissolved  oxygen  in  water,  as  a  means  of  ascertaining  the 
co-existence  of  the  two  kinds  of  impurity. 

In  brewing  also  a  knowledge  of  the  state  of  aeration  of  the  wort 
is  sometimes  of  importance,  especially  at  the  fermentation  stage  of 
the  process. 


§  68.  OXYGEN.  255 

Several  methods  have  been  proposed  for  carrying  out  the 
estimation.  Mohr's  method,  depending  on  the  oxidation  of  ferrous 
compounds,  with  subsequent  titration  by  permanganate,  has  not 
come  greatly  into  use.  Winkler  (Bericlite  1888,  2851)  has  quite 
recently  proposed  to  take  advantage  of  the  oxidation  of  manganous 
hydroxide*  by  dissolved  oxygen,  the  higher  oxide  formed 
being  decomposed  by  sulphuric  acid  and  potassic  iodide  with 
liberation  of  iodine,  which  is  estimated  by  titration  with  sodic 
thiosulphate.  This  method  is  disturbed  by  the  presence  of  nitrites, 
which  also  liberate  iodine  from  acidified  potassic  iodide ;  great 
organic  contamination  also  interferes,  inasmuch  as  the  impurities 
present  take  up  a  portion  of  the  liberated  iodine. 

Schiitzeiiberger's  method,!  fully  described  in  the  last  edition 
of  this  book,  has  received  great  attention  from  many  operators, 
some  of  whom  have  reported  favourably,  whilst  others  find  the 
process  unreliable.  The  reason  for  the  anomalies  apparent  in  the 
reports  of  the  various  experimenters  is  shown  in  the  results  of  an 
interesting  critical  investigation  of  the  process  carried  out  by 
E-oscoe  and  Lunt  (J".  G.  S.  1889,  552).  They  show  that  an 
important  disturbing  influence  had  been  overlooked,  and  explain 
many  previously  ill-understood  points  in  the  process. 

Schiitzenberger's  original  process  depends  on  the  reducing 
action  of  sodic  hyposulphite  Na2S02,  prepared  by  the  action  of 
zinc  dust  on  a  saturated  solution  of  sodic  bisulphite,  containing 
an  excess  of  sulphurous  acid.  The  estimation  was  originally 
carried  out  in  a  large  Woullf  's  bottle,  of  about  two  liters  capacity, 
filled  with  pure  hydrogen.  About  20 — 30  c.c.  of  water  was 
introduced,  and  slightly  coloured  blue  by  indigo-carmine  solution. 
The  blue  colour  was  then  cautiously  discharged  by  the  careful 
dropping  in  of  hyposulphite  solution.  To  the  yellow  reduced 
liquid  thus  produced,  the  water  to  be  examined  was  added  from 
a  pear-shaped  vessel  holding  about  250  c.c.  The  dissolved  oxygen 
restored  the  blue  colour  by  oxidation,  and  the  amount  of  hypo- 
sulphite required  to  again  decolorise  the  liquid  was  noted. 

Schiitzenberger  showed  that  when  a  small  amount  of  indigo 
was  employed  in  the  estimation,  the  yellow  colour  produced  when 
the  titration  was  completed  quickly  returned  to  blue,  and  this 
when  decolorized  again  turned  blue,  and  so  on  for  some  time,  until 
double  the  first  amount  of  hyposulphite  had  been  used.  He 
showed  also  that  by  using  a  much  larger  amount  of  indigo  the 
double  portion  of  hyposulphite  was  required  at  once. 

By  titrating  an  ammoniacal  solution  of  copper  sulphate  with  the 
hyposulphite  used  he  arrived  at  a  value  (though  an  erroneous  one) 
for  the  hyposulphite  employed  in  his  experiments,  and  concluded 
that,  at  the  first  yellow  colour  produced  in  a  titration  where 
a  small  amount  of  indigo  was  used,  only  half  the  oxygen  actually 

*  Obtained  by  mixing  solutions  of  a  manganous  salt  and  caustic  alkali. 
tSee  Fermentation  by  P.  Schiitzenberger  (International  Scientific  Series). 


256  VOLUMETKIC   ANALYSIS.  §    68. 

present  had  been  obtained.  The  other  half  he  accounted  for  by 
saying  that  the  reaction  between  hyposulphite  and  dissolved  oxygen 
is  such,  that  one-half  the  oxygen  becomes  latent  as  hydrogen 
peroxide,  which  slowly  gives  up  half  its  oxygen.  He  thus  accounted 
for  the  return  of  the  blue  colour,  as  well  as  his  observation  that 
only  half  the  oxygen  was  at  once  obtained.  To  explain  the 
observation,  that  when  a  large  amount  of  indigo  was  employed 
the  whole  of  the  dissolved  oxygen  was  found,  he  assumed  that 
a  different  reaction  takes  place,  one  between  dissolved  oxygen  and 
reduced  indigo,  in  which  the  peroxide  of  hydrogen  is  not  formed. 

Ramsay  and  Williams  (/.  C.  S.  1886,  751),  whilst  agreeing 
with  Schiitzeiiberger  and  with  Dupre,*  that  the  process  gives 
reliable  results,  throw  a  doubt  on  the  chemical  explanation  given 
of  the  above  experiments. 

Instead  of  the  ratio  1  :  2,  they  find  3  :  5  to  be  the  ratio 
between  the  first  and  total  quantity  of  hyposulphite  required  when 
a  small  amount  of  indigo  is  employed,  but  give  it  only  as  the  mean 
expression  of  the  varying  ratios  they  obtain,  and  add,  "  but  it  is 
difficult  to  devise  an  equation  which  will  in  a  rational  manner 
account  for  this  partition  of  oxygen"  into  two  stages  of  the 
process.  Roscoe  and  Lunt's  investigation  (/.  C.  JS.  1889,  552) 
has  thrown  a  new  light  on  these  experiments.  They  show  (1)  that 
a  series  of  fifteen  estimations  carried  out  with  every  care  in 
improved  apparatus,  and  under  apparently  identical  conditions, 
gave  discordant  results,  varying  between  4 '55  and  6 '50  c.c.  of 
hyposulphite  for  the  same  volume  of  water,  showing  a  difference 
of  35  per  cent,  of  the  mean  value.  (2)  The  rapidity  of  titratioii 
has  a  great  influence  on  the  result.  The  mean  of  a  series  of  ten 
estimations  carried  out  drop  by  drop  was  5 '47,  whilst  ten 
experiments  with  the  same  sample  of  water  gave  a  mean  of  7 '12 
when  the  titration  was  performed  quickly.  (3)  Not  only  is 
a  low  result  obtained  by  a  slow  titration  and  a  high  result  by 
a  quick  one,  but  by  varying  the  time  of  titration  still  more,  extreme 
variations  in  the  result  are  obtained ;  any  value  between  1  and  100 
per  cent,  of  the  total  oxygen  present  being  shown  to  be  possible. 
(4)  The  ratio  between  the  first  reading  and  the  total  quantity 
of  hyposulphite  required  is  not  a  constant  one,  and  is  shown  to 
be  capable  of  an  infinite  range  of  variation. 

The  key  to  the  explanation  of  these  remarkable  results  is  given 
by  the  authors  as  follows  : — "  The  conclusion  "  from  their  experi- 
ments "  was,  that  when  aerated  water  is  introduced  into  an 
atmosphere  of  pure  hydrogen,  it  immediately  begins  to  lose  oxygen 
by  diffusion  into  the  hydrogen  until  an  equilibrium  is  established." 
By  the  recognition  of  this  disturbing  influence,  the  previous 
anomalies  are  easily  explainable  on  the  following  data. 

(1)  Discordant  results  are  obtained  from  the  same  water, 
because  the  several  titrations  are  not  performed  in  exactly  the  same 

*  Analyst  x.  156. 


§  68. 


OXYGEN. 


257 


time,  therefore,  varying   amounts   of   oxygen   diffuse,   and   leave 
a  varying  residue  for  titration. 

(2)     The  high  results  of  a  quick  titration  are  accounted  for  by 
the  fact  that  a  large  amount  of  oxygen  is  titrated  and  fixed  before 


Fig.  42. 

it  has  had  time  to  diffuse,  whilst  the  slow  titration  gives  a  low 
result,  because  a  large  amount  of  oxygen  has  already  diffused 
from  the  liquid  before  the  titration  is  completed.  No  greater 
proof  of  the  rapidity  with  which  the  water  under  examination  lost 


258  VOLUMETRIC   ANALYSIS.  §    68. 

oxygen  by  the  old  process  need  be  given  than  the  fact,  that 
Schiitzenberger's  results  show  that  half  the  oxygen  had  left  the 
liquid  by  diffusion  before  the  estimation  could  be  completed. 

(3)  The  return  of  the  blue  colour  is  clue  to  the  re-absorption 
of  the  diffused  oxygen  by  the  sensitive  yellow  liquid,  oxidation  by 
gaseous  oxygen  producing  the  blue  colour,  which  is  thus  not  due 
to  a  reaction  within  the  liquid. 

(4)  The  whole  of  the  oxygen  is  obtained  when  a  large  amount 
of  indigo  is  used,  because  when  reduced  it  is  capable  of  at  once 
fixing   the   whole   of    the   dissolved    oxygen   and    thus   prevents 
diffusion.     The  use  of  so  large  a  quantity  of  indigo,  necessary  to 
effect  this  result,  however,  so  disturbs  the  end  reaction  that  "  it  is 
difficult  to  fix  the  point  at  which  the  last  trace  of  blue  has  been 
discharged  with  any  degree  of  accuracy"  (Dupre  loc.  vit.\     Hence 
a  new  method  must  be  resorted  to  in  which  diffusion  is  eliminated, 
and  Koscoe  and  Lunt  have  devised  the  following  method  to 
satisfy  the  conditions  of  the  case.     The  apparatus  employed  by 
them  is  shown  in  fig  42. 

It  consists  essentially  (1)  of  an  apparatus  for  the  continuous 
generation  and  purification  of  hydrogen,  by  the  action  of  dilute 
sulphuric  acid  on  zinc ;  (2)  a  200  c.c.  wide-mouthed  bottle,  fitted 
with  three  burettes  with  glass  taps,  inlet  and  outlet  tubes  for  a 
current  of  hydrogen,  and  an  outlet  tube  for  the  titrated  liquid; 
(3)  Winchester  stock  bottles  of  hyposulphite,  indigo  (not  shown), 
and  water  (sample),  communicating  with  their  respective  burettes 
by  glass*  syphons.  The  hydrogen  generated  in  A  passes  through 
two  wash-bottles  containing  caustic  potash,  thence  through  two 
Emmerling's  tubes  filled  with  glass  beads,  moistened  with  an 
alkaline  solution  of  potassic  pyrogallate,  an  arrangement  being 
made  whereby  the  beads  may  be  re-moistened  with  fresh  pyrogallate 
from  the  bottles  beneath,  the  liquid  being  forced  up  by  hydrogen 
pressure.  Pure  hydrogen  is  supplied  continuously  (1)  to  the 
stock  bottle  of  hyposulphite,  (2)  to  the  hyposulphite  burette,  and 
(3)  to  the  titration  bottle. 

Preparation  of  the  Reagents. — The  reagents  required  are — 
Hyposulphite  solution. 
Indigo-carmine  solution. 
Standard  aerated  distilled  water. 

The  Hyposulphite  solution  is  prepared  by  dissolving  125  gin.  of 
sodic  bisulphite  in  250  c.c.  of  water,  and  passing  a  current  of  SO2 
through  the  solution  until  saturation  is  effected.  The  solution  is 
poured  into  a  stoppered  bottle  of  about  500  c.c.  capacity,  containing 
50  gm.  of  zinc  dust,  the  bottle  is  almost  filled  up  with  water,  and 
the  mixture  well  shaken  for  five  minutes,  after  which  the  bottle  is 

*  India-rubber  tubing  must  not  be  used  for  the  conveyance  of  the  hyposulphite 
solution  (or  the  water  under  examination),  as  atmospheric  oxygen  rapidly  diffuses 
through  the  india-rubber  and  affects  the  strength  of  the  solution. 


§    68.  OXYGEN.  259 

placed  beneath  a  running  tap  to  cool.  The  mixture  is  again 
agitated  after  a  quarter  of  an  hour  and  left  to  deposit  the  excess  of 
zinc.  The  clear  liquid  is  poured  off  from  the  sediment  into  a 
Winchester  quart  bottle  half  full  of  water.  Milk  of  lime  is 
added  in  excess,  and  the  solution  made  up  to  fill  the  bottle  almost 
completely.  The  mixture  is  now  thoroughly  shaken  and  allowed 
to  stand  (best  overnight)  until  clear. 

The  solution  thus  obtained  is  much  too  strong  for  use.  200  c.c. 
of  this  may  be  poured  into  a  Winchester  quart  bottle  of  water 
(never  into  a  bottle  filled  with  air)  and  well  shaken  with  as  little 
air  as  possible.  The  approximate  strength  of  this  dilute  solution 
must  now  be  found  by  titrating  good  tap  water  in  the  apparatus 
already  described.  The  strength  should  be  such  that  100  c.c.  of 
water  require  about  5  c.c.  of  hyposulphite,  and  the  solution  should 
be  made  up  approximately  to  this  value.  It  slowly  loses  strength 
on  keeping,  even  in  hydrogen,  and  its  value  should  be  determined 
daily  as  required  to  be  used. 

The  Indigo-carmine  solution  is  prepared  by  shaking  up  200  gm. 
of  indigo-carmine  in  a  Winchester  quart  bottle  of  water,  and 
filtering  the  blue  solution,  which  must  be  diluted  to  such  a  strength 
that  20  c.c.  require  about  5  c.c.  of  the  above  hyposulphite  solution 
for  decolorisation. 

Standard  Aerated  Distilled  "Water. — Two  Winchester  quart  bottles 
half  filled  with  freshly  distilled  water  are  vigorously  agitated  for 
five  minutes,  and  the  air  renewed  several  times  by  filling  up  one 
bottle  with  the  contents  of  the  other,  and  again  dividing  into  two 
portions,  which  are  repeatedly  shaken  with  fresh  air.  Finally,  one 
bottle  being  filled,  the  temperature  of  the  water  is  taken,  and  also 
the  barometric  pressure,  after  which  the  bottle  is  allowed  to  stand 
stoppered  for  half  an  hour,  to  get  rid  of  minute  air-bubbles.  The 
following  table,  due  to  Roscoe  and  Lunt,  gives  the  volume  of 
oxygen  contained  in  this  standard  aerated  water,  and  the  results 
show  that  Bun  sen's  co-efficients,  previously  used,  are  inaccurate. 


260 


VOLUMETKIC   ANALYSIS. 


68. 


Oxygen   Dissolved  by   Distilled  Water.     5—30°  C. 


Temp. 
C. 

c.c.  Oxvgen 
N.T.P. 

per  liter  Aq, 

Diff.  for 
0'5°  C. 

Temp. 
C. 

c.c.  Oxygen 
N.T.P. 
per  liter  Aq. 

Diff.  for 
0-5°  C. 

5-0° 

8-68 

18-0° 

6-54 

0'07 

5-5 

8-58 

o-io 

18-5 

6-47 

0-07 

6-0 

8'49 

0-09 

19-0 

6-40 

0-06 

6-5 

8-40 

0'09 

195 

6'34 

0-06 

7-0 

8-31 

0-09 

20-0 

6-28 

0'06 

7-5 

8-22 

0-09 

20-5 

6-22 

0-06 

8-0 

8'13 

0-09 

21'0 

6-16 

0-06 

8-5 

8-04 

0'09 

21-5 

6-10 

0-06 

90 

7-95 

0-09 

22-0 

6-04 

0-05 

9'5 

7-86 

0-09 

22-5 

5'99 

0'05 

10-0 

777 

0-09 

23-0 

5-94 

0'05 

10-5 

7-68 

0'08 

23'5 

5-89 

0-05 

11-0 

7-60 

0-08 

24-0 

5-84 

0-04 

11-5 

7'52 

0-08 

24-5 

5-80 

0-04 

12-0 

7'44 

0-08 

25-0 

576 

0'04 

12-5 

7'36 

008 

25'5 

5-72 

0'04 

13-0 

7-28 

0-08 

26'0 

5-68 

0'04 

13-5 

7-20 

0-08 

26-5 

5-64 

0-04 

14-0 

7-12 

0'08 

27-0 

5'60 

0-03 

14-5 

7-04 

0-08 

27-5 

5-57 

0'03 

15-0 

6-96 

0-08 

28-0 

5-54 

0-03 

15-5 

6-89 

0-07 

28-5 

5-51 

0-03 

16-0 

6'82 

0-07 

29-0 

5'48 

0-03 

16-5 

6'75 

0-07 

29-5 

5-45 

0'02 

17-0 

6-68 

0-07 

30-0 

5-43 

17-5 

6'61 

0-07 

In  this  table  the  results  are  calculated  for  aeration  at  an  observed 
barometric  pressure  of  760  mm.  "When  the  observed  pressure  is  below 
760  mm.  ^th  the  value  must  be  subtracted  for  every  10  mm.  diff.  The 
same  value  must  be  added  when  the  pressure  is  above  760  mm. 

The  Estimation :  The  burettes  having  been  filled,  and  a  preliminary  trial 
made— 

(1)  20  c.c.  of  the  water  is  introduced  into  the  small  bottle  and  about  3  c.c. 
of  indigo  solution  added. 

(2)  A  moderate  current  of  hydrogen  is  passed  through  the  blue  liquid  by 
a  very  fine  jet  for  three  minutes  to  free  both  water  and  supernatant  gas  from 
free  hydrogen. 

(3)  Hyposulphite  is  now  carefully  added,  during  the  flow  of  hydrogen, 
until  the  change  from  blue  to  yellow  occurs,  taking  care  not  to  overstep  this 
point. 

(4)  A  further  measured  quantity  of  hyposulphite  is  now  added  (say  10  c.c.) 
sufficient  to  combine  with  all  the  dissolved  oxygen  in  the  volume  of  water 
(50 — 100  c.c.)  proposed  to  be  used  in  the  estimation. 

(5)  The  important  point  is,  that  the  water  is  now  quickly  run  in  from  a 
burette  by  a  capillary  tube  passing  beneath  the  surface  of  the  liquid  to  the 
bottom  of  the  vessel.     The  water  is  thus  introduced  into  a  liquid  which  will 
at  once  fix  the  free  oxygen  and  thus  prevent  its  diffusion  on  coming  in 
contact  with  the  hydrogen,  the  reduced  indigo  acting  as  an  indicator  for  the 


§    68.  OXYGEN.  261 

complete  oxidation  of  the  hyposulphite.  The  liquid  is  kept  in  constant 
motion  during  the  addition  of  the  water,  which  is  shut  off  the  moment  a 
permanent  blue  colour  appears. 

(6)  The  blue  is  decolorized  by  a  further  slight  addition  of  hyposulphite. 
The  volume  of  water  used  and  the  total  hyposulphite,  minus  the  first  addition, 
are  noted  and  the  estimation  repeated  for  confirmation. 

When  the  water  contains  very  little  oxygen  the  second  addition 
of  hyposulphite  may  be  omitted,  the  reduced  indigo-carmine  being 
sufficient  to  take  up  all  the  dissolved  oxygen.  In  this  case,  care 
must  be  taken  that  the  oxygen  added  should  require  not  more 
than  half  the  hyposulphite  first  added  to  decolorize  the  indigo- 
carmine. 

Standardizing-  the  Hyposulphite. — In  order  to  complete  the 
estimation  it  is  necessary  to  know  the  strength  of  the  hyposulphite 
solution  employed,  and  for  this  purpose  the  bottle  of  standard 
aerated  distilled  water  is  titrated.  This  method  has  the  great 
advantage  that  it  is  a  titration  carried  out  under  almost  the  same 
conditions  as  the  examination  of  the  sample.  The  result  of  an 
estimation  is  easily  obtained  by  the  following  formula — 

dxhsxOd 

•  =x  c.c.  O  per  liter  of  water 


where  d  and  s  =  the  volumes  of  distilled  water  and  sample  re- 
spectively used,  and  lid  and  lis  =  the  hyposulphite  required  for  the 
distilled  water  and  sample  respectively,  and  Od  the  volume  of 
dissolved  oxygen  contained  in  one  liter  of  the  standard  water. 

Standardizing:  the  Indigo. — When  once  the  hyposulphite  has 
been  carefully  standardized  by  distilled  water,  the  rather  trouble- 
some aeration  may  be  avoided  by  finding  the  oxygen-value  of  the 
indigo-carmine  solution.  This  solution  remaining  constant  may  be 
used  for  the  subsequent  standardizing  of  the  hyposulphite. 

It  is  only  necessary  to  take  a  suitable  quantity  of  indigo  solution, 
diluted  with  water  if  necessary,  free  it  from  all  dissolved  oxygen 
by  a  current  of  pure  hydrogen  continued  for  five  minutes,  then 
carefully  decolorize  with  hyposulphite,  the  value  of  which  has  been 
found  by  using  aerated  distilled  water. 

The  authors  show  that  Schutzenberger's  method  of  standard- 
ization, depending  on  the  decolorization  of  ammoniacal  copper 
sulphate,  gives  inaccurate  results. 

Free  acids  or  alkalies  greatly  disturb  the  process.  Bicarbonates 
have  no  effect.  Of  course  when  other  substances  than  oxygen, 
which  decompose  hyposulphite,  are  present,  the  accuracy  of  the 
method  is  proportionately  disturbed.  The  authors  have  applied  the 
process  to  waters  of  very  varied  character,  and  containing  widely 
different  amounts  of  oxygen,  and  show  that  the  method  is  capable 
of  giving  good  results,  compared  with  the  actual  volume  of  oxygen 
found  by  extracting  the  gases  by  boiling  in  vacua. 


262 


VOLUMETKIC  ANALYSIS. 


68. 


The  delicacy  of  the  reaction  is  such  that  one  part  of  oxygen  in. 
two  million  parts  of  water  is  easily  detected. 

The  following  numbers  were  obtained  from  five  different  samples 
of  London  tap-water  collected  on  five  different  days. 


(1) 

(2) 

(3) 

(4) 

(5) 

Nitrogen 

c.c. 
1322 
5-15 

7'98 

c.c. 
13-95 
5-91 
9-29 

c.c. 
13-36 
5-38 
6'VO 

c.c. 
13-43 
6-31 
7'35 

c.c. 
13-49 
5-80 
8-11 

Oxygen 

Carbonic  acid             

Total  otis 

26-35 

2915 

25-44 

27-09 

27-40 

Oxygen    by    the    new 
volumetric  method... 
Gas  obtained 

5-52 
5-15 

6-13 
5-91 

5-64 
5-38 

6-41 
631 

6'24 
5-80 

Difference  

0-37 

0-22 

0-26 

O'lO 

0'44 

Mean  difference  0*28  c.c.  oxygen  per  liter  of  water. 

The  oxygen  values  obtained  by  the  two  methods  show  close 
agreement,  considering  the  possible  experimental  error  in  so  complex 
a  comparison. 


lodometric    Method. 

A  simpler  method  than  the  foregoing  has  been  proposed  by 
Thresh  (/.  C.  S.  Ivii.  185)  which  by  comparison  with  Roscoe 
and  Lunt's  method  appears  to  give  satisfactory  results  when 
aerated  distilled  water  was  under  titration,  the  differences  occurring 
only  in  the  second  decimal  place.  The  author  was  led  to 
investigate  the  method  by  observing  the  large  amount  of  iodine 
which  a  very  minute  quantity  of  a  nitrite  caused  to  be  liberated, 
when  potassic  iodide  and  dilute  sulphuric  acid  were  added  to  water 
containing  it.  The  amount  of  iodine  liberated  varies  with  the 
length  of  exposure  to  air.  If  air  is  excluded  no  increase  of  free 
iodine  occurs  after  the  first  few  minutes,  and  if  the  water  is 
previously  boiled  and  cooled  in  an  air-free  space  still  less  iodine  is 
liberated.  In  this  latter  case  the  action  is  represented  by  the 
equation — 

2HI  +  2HN02  =  I2  +  2H20  +  2^0. 

When  oxygen  has  access  to  the  solution,  the  nitric  oxide  acts  as 
a  carrier,  and  more  hydrogen  iodide  is  decomposed,  the  nitric  oxide 
apparently  remaining  unaffected,  and  capable  of  causing  the 
decomposition  of  an  unlimited  quantity  of  the  iodide. 


§    68.  OXYGEN.  263 

This  reaction  is  the  one  utilised  in  the  process  devised  by 
Thresh  for  estimating  the  oxygen  dissolved  in  water.  As  16  parts 
by  weight  of  oxygen  will  liberate  254  parts  of  iodine,  thus  — 


and  as  the  latter  element  admits  of  being  accurately  estimated, 
theoretically  the  oxygen  should  be  capable  of  very  precise 
determination.  Practically  such  is  the  case  ;  the  oxygen  dissolved 
in  drinking  waters  admits  of  being  estimated  both  rapidly  and 
with  precision.  It  is  only  necessary  to  add  to  a  known  volume  of 
the  water  a  known  quantity  of  sodic  nitrite,  together  with  excess 
of  potassic  iodide  and  acid,  avoiding  access  of  air,  and  then  to 
determine  volumetrically  the  amount  of  iodine  liberated.  After 
deducting  the  proportion  due  to  the  nitrite  used,  the  remainder 
represents  the  oxygen  which  was  dissolved  in  the  water  and  in  the 
volumetric  solution  used. 

The  following  are  the  reagents  required  :  — 

(1)  Solution  of  sodic  nitrite  and  potassic  iodide  :  — 

Sodic  nitrite    ...........................       0'5  gm. 

Potassic  iodide    ........................     20*0  gm. 

Distilled  water    ........................     100  c.c. 

(2)  Dilute  sulphuric  acid  :  — 

Pure  sulphuric  acid    ..................     1  part. 

Distilled  water    ..............  .  .........     3  parts. 

(3)  A  clear  fresh  solution  of  starch. 

(4)  A  volumetric  solution  of  sodic  thiosulphate  :  — 

Pure  crystals  of  thiosulphate,  7*75  gm. 

Distilled  water  to  1  liter. 

1  c.c.  corresponds  to  0*25  milligram  of  oxygen. 

The  apparatus  required  is  very  simple,  and  can  readily  be  fitted 
up.  It  consists  of  a  wide-mouthed  white  glass  bottle  (A,  fig.  43) 
of  about  500  c.c.  capacity,  closed  with  a  caoutchouc  stopper  having 
four  perforations.  Through  one  passes  the  tube  B,  drawn  out  at 
its  lower  extremity  to  a  rather  fine  point,  and  connected  at  the 
upper  end,  by  means  of  a  few  inches  of  rubber  tubing,  with  the 
burette  C,  containing  the  thiosulphate.  Through  another  opening 
passes  the  hozzle  of  a  separatory  tube  D,  having  a  stopper  and 
stopcock.  The  capacity  of  this  tube  when  full  to  the  stopper 
must  be  accurately  determined.  Through  the  third  opening  passes 
a  tube  E,  which  can  be  attached  to  an  ordinary  gas  supply.  Through 
the  last  aperture  is  passed  another  tube,  for  the  gas  exit,  and  to 
this  is  attached  a  sufficient  length  of  rubber  tubing  to  enable  the 
cork  G  at  its  end  to  be  placed  in  the  neck  of  the  tube  D  when  the 


264 


VOLUMETRIC   ANALYSIS. 


§    68. 


stopper  is  removed.     A  small  piece  of  glass  tube  projects  through 
the  cork,  to  allow  of  the  escaping  gas  being  ignited. 

The  apparatus  is  used  in  the  following  manner  : — The  bottle  A 
being  cleaned  and  dry,  the  perforated  bung  is  inserted,  the  burette 
charged,  and  the  tube  B  fixed  in  its  place.  E  is  connected  with 
the  gas  supply.  The  tube  D  is  filled  to  the  level  of  the  stopper 
with,  the  water  to  be  examined,  1  c.c.  of  the  solution  of  sodic 
nitrite  and  potassic  iodide  added  from  a  1  c.c.  pipette,  then  1  c.c. 
of  the  dilute  acid,  and  the  stopper  instantly  fixed  in  its  place, 
displacing  a  little  of  the  water,  and  including  110  air.  If  the 
pipette  be  held  in  a  vertical  position  with  its  tip  just  under  the 
surface  of  the  water,  both  the  saline  solution  and  the  acid,  being 
much  denser  than  the  water,  flow  in  a  sharply  defined  column  to 
the  lower  part  of  the  tube,  so  that  an  infinitesimally  small  quantity 


A 


Fig.  43. 

(if  any)  is  lost  in  the  water  which  overflows  when  the  stopper  is 
inserted.  The  tube  is  next  turned  upside  down  for  a  few  seconds 
for  uniform  admixture  to  take  place,  and  then  the  nozzle  is  pushed 
through  the  bung  of  the  bottle,  and  the  whole  allowed  to  remain 
at  rest  for  15  minutes,  to  enable  the  reaction  to  become  complete. 
A  rapid  current  of  coal  gas  is  now  passed  through  the  bottle  A, 
until  all  the  air  is  displaced  and  the  gas  burns  at  G  with  a  full 
luminous  flame ;  the  flame  is  now  extinguished,  the  stopper  of  D 


§68.  OXYGEN.  265 

removed,  and  the  cork  G-  rapidly  inserted.  On  turning  the  stop- 
cock, the  water  flows  into  the  bottle  A.  The  stopcock  is  turned 
off,  the  cork  G  removed,  and  the  supply  of  gas  regulated  so  that 
a  small  flame  only  is  produced  when  this  gas  is  ignited  at  G. 
Thiosulphate  is  now  run  in  slowly  until  the  colour  of  the  iodine  is 
nearly  discharged.  A  little  solution  of  starch  is  then  poured  into 
D,  and  about  1  c.c.  allowed  to  flow  into  the  bottle  by  turning  the 
stopcock.  The  titration  with  thiosulphate  is  then  completed. 
After  the  discharge  of  the  blue  colour,  the  latter  returns  faintly  in 
the  course  of  a  few  seconds,  due  to  the  oxygen  dissolved  in  the 
volumetric  solution;  after  standing  about  two  minutes,  from  0*05 
to  O'l  c.c.  of  thiosulphate  must  be  added  to  effect  the  final 
discharge.  The  amount  of  volumetric  solution  used  must  now  be 
noted.  This  will  represent  a,  the  oxygen  dissolved  in  the  water 
examined,  +  b,  the  nitrite  in  the  1  c.c.  of  solution  used,  and  the 
oxygen  in  the  acid  and  starch  solution  +  c,  a  portion  of  the  dissolved 
oxygen  in  the  volumetric  solution.  To  find  the  value  of  a,  it  is 
obvious  that  b  and  c  must  be  ascertained.  This  can  be  effected  in 
many  ways,  and  once  known  does  not  require  re-determination 
unless  the  conditions  are  changed. 

To  Find  the  Value  of  b. — Probably  the  best  plan  is  to  complete 
a  determination  as  above  described,  and  then,  by  means  of  the 
stoppered  tube,  introduce  into  the  bottle  in  succession  5  c.c.  of 
nitrite  solution,  dilute  acid,  and  starch  solution.  After  standing 
a  few  minutes,  titrate.  One-fifth  of  the  thiosulphate  used  will  be 
the  value  required. 

To  Find  the  Value  of  c. — This  correction  is  a  comparatively 
small  one,  and  admits  of  determination  with  sufficient  accuracy  if 
it  is  assumed  that  the  thiosulphate  solution  normally  contains  as 
much  dissolved  oxygen  as  distilled  water  saturated  at  the  same 
temperature.  Complete  a  determination  as  above  described,  then 
remove  the  stoppered  tube,  and  insert  a  tube  similar  to  that 
attached  to  the  burette,  and  drop  in  from  it  10  or  20  c.c.  of 
saturated  distilled  water  exactly  as  the  thiosulphate  is  dropped  in. 
Allow  to  stand  a  few  minutes  and  titrate.  One-tenth  or  one- 
twentieth  of  the  volumetric  solution  used,  according  to  the 
number  of  c.c.  of  water  added,  will  represent  the  correction  for  each 
c.c.  of  volumetric  solution  used.  Call  this  value  d. 

Let  e  be  the  number  of  c.c.  of  thiosulphate  used  in  an  actual 
determination  of  the  amount  of  oxygen  in  a  sample  of  water  ; 

/=the  capacity  in  c.c.  of  the  tube  employed-  2  c.c.,  the  volume 

of  reagents  added ; 
g  =  the  amount  of  oxygen  in  milligrams  dissolved  in  1  liter  of 

the  water ; 

then  ( 


266  VOLUMETRIC  ANALYSIS.  §    68. 

"With  a  tube  made  to  hold  exactly  250  c.c.,  the  most  convenient 

1  000 
quantity  to  use, —  becomes  unity,  and 

g=  e  —  b  —  ed. 

In  the  author's  experiments  two  nitrite  solutions  were  used; 
in  the  first  1  =  2 '1  c.c.,  in  the  second  3'1  c.c.  A  number  of 
determinations  of  d  were  made,  at  temperatures  varying  from 
40°  to  60°  F.  The  value  of  d  was  found  to  vary  between  0*03 
and  0-0315.  In  all  the  author's  recent  experiments  d  was  taken 
as  0-031. 

When  e  =  3  c.c.  the  reaction  seems  to  be  complete  in  five 
minutes,  but,  to  be  on  the  safe  side,  it  is  better  to  fix  the  minimum 
at  fifteen  minutes. 

The  use  of  coal-gas  is  recommended  by  the  author  without 
passing  it  over  alkaline  pyrogallol  or  otherwise  treating  it  before 
allowing  it  to  pass  through  the  apparatus. 

The  results  obtained,  however,  can  be  made  to  vary,  the  extreme 
limit  being  less  than  0'5  milligram  of  oxygen  per  liter  of  water, 
using  250  c.c.  for  the  estimation.  To  quote  an  extreme  case.  In 
one  experiment  (1),  after  the  air  had  been  wholly  expelled  from 
the  bottle  A,  no  more  gas  was  passed  through,  and  the  titration 
was  effected  in  the  closed  apparatus,  the  volumetric  solution  being 
run  in  as  rapidly  as  possible.  The  end  reaction  was  not  well 
defined.  In  the  second  experiment  (2),  the  volumetric  solution 
was  run  in  very  slowly  drop  by  drop,  and  a  brisk  current  of  gas 
was  kept  passing  through  the  apparatus.  End-reaction  well 
defined. 

Volume  of  water.  Thiosulphate.  Oxygen  per  liter. 

(1)  322  c.c.  15-35  c.c.  9 -14  milligrams. 

(2)  322    „  14-9      „  8-80 

The  difference  is  probably  due  to  nearly  all  the  oxygen  dissolved 
in  thiosulphate  being  used  up  in  the  first  case,  and  being  lost  by 
diffusion  in  the  second. 

In  the  examination  of  waters  from  various  sources,  and  making 
the  experiments  in  pairs,  using  tubes  of  different  sizes,  the  author 
found  that  exceedingly  concordant  results  could  easily  be 
obtained. 

In  estimating  the  oxygen  in  distilled  water  saturated  with  air, 
the  author  found  that  the  results  at  25°  and  30°  C.  were  higher 
than  those  obtained  by  Koscoe  and  Lunt,  whilst  at  the  lower 
temperatures  they  were  almost  identical,  and  it  occurred  to  him  that 
the  difference  was  probably  due  to  the  mode  of  saturation.  The 
agitation  in  a  couple  of  Winchesters  was  done  as  directed  by 
them,  but  the  water  used  had  been  previously  saturated  at  the 


§  68. 


OXYGEN. 


267 


lower  temperatures,  and  probably  was  slightly  super-saturated. 
A  further  series  of  experiments  were  then  made  with  freshly- 
distilled  water,  which  was  not  agitated  with  air  until  it  had 
attained  the  desired  temperature.  The  results  proved  that  this 
surmise  was  correct.  Probably  some  such  explanation  accounts  for 
the  uniformly  higher  results  obtained  by  Dittmar. 

No  doubt  there  will  be  exceptional  cases  in  which  the  process 
cannot  be  used,  and  others  in  which  some  modification  may  be 
required.  A  water  containing  nitrites  will  require  the  amount  of 
the  nitrous  acid  to  be  determined  if  the  utmost  accuracy  is 
required.  (A  water  containing  1  part  of  HNO2  in  1,000,000,  will 
affect  the  results  +  0*17  milligram  of  oxygen  per  liter,  94  parts 
of  the  acid  corresponding  to  16  of  oxygen).  Where  nitrites  are 
present  in  sufficient  quantity  to  interfere,  the  amount  may  be 
determined  by  any  of  the  ordinary  processes,  but  the  author 
prefers  the  following  method  : — 

To  250  c.c.  of  the  water  to  be  examined,  rendered  faintly 
alkaline  if  not  already  so,  add  a  few  drops  of  strong  solution  of 
potassic  iodide,  and  boil  vigorously  for  a  few  minutes.  Then 
transfer  to  the  bottle  A  used  in  the  oxygen  determination,  and 
allow  to  get  quite  cold  in  a  slow  current  of  coal  gas.  Then  add 
a  few  drops  of  dilute  sulphuric  acid  and  solution  of  starch,  and 
titrate  with  the  thiosulphate.  The  correction  to  be  made  in  the 
oxygen  determination  is  thus  ascertained.  One  or  two  experi- 
mental results  may  be  quoted. 


Quantity 
of  water. 

Thiosulphate 
used. 

Corrected. 

Milligrams  of 
oxygen  per  liter. 

1 

Tap  water 

232'  5 

132 

9'7 

10'43 

2  j 

Tap  water  +  5  milli- 
grams    commercial 
sodic  nitrite 

1  232-5 

15-95 

9-55 

1027 

»{ 

Tap  water  +  10  milli- 
grams sodic  nitrite 

|  232-5 

18-6 

9'48 

10-19 

In  number  2,  the  thiosulphate  used  by  250  c.c.  of  the  boiled 

water  was  2*8  c.c. 
In  number  3,  the  thiosulphate  used  by  250  c.c.  of  the  boiled 

water  was  5 -4 5  c.c. 


The  results  are  fairly  satisfactory,  even  with  such  large 
proportions  of  nitrite,  proportions  far  larger  than  are  likely  to  be 
met  with  in  practice. 

Nitrates  do  not  interfere,  even  when  present  in  large  quantities ; 
but  fresh  urine,  when  present  to  the  extent  of  1  per  cent.,  has 
a  small  but  very  appreciable  effect. 


268 


VOLUMETRIC  ANALYSIS. 


§    68- 


The    following    is   an    example    of    the    method    at   ordinary 
temperature  : — 

Temperature    15°    C. 


Quantity  of 
water  taken. 

Thiosulphate 
used. 

e  _  b  —  ei. 

Milligrams  of 
Oxygen  per  liter. 

Difference 
from  mean. 

1... 

2... 
3... 
4... 

322-0 
322-0 
232-5 
232-5 

15-45 
15-55 
11-90 
11-70 

12-87 
12-97 
9-43 
9-23 

Mean... 

9-99 
10-07 
10-14 
9-92 

—0-04 
+  0-04 

+0-11 
—o-ii 

1003 

Barometer  reading  30  in. 
10-03  milligrams=7'02  c.c.  at  N.P.T. 


Roscoe  and  Lunt  found  6'96 


Difference  +  0'06. 


HYDROGEN    PEROXIDE. 

H202  =  34. 

This  substance  is  now  largely  used  in  commerce,  and  is  sold 
as  containing  5,  10,  or  20  volumes  of  oxygen  in  solution.  This 
should  mean  that  the  specified  number  of  volumes  can  be  obtained 
from  the  solution  itself,  but  preparations  are  sent  into  the  market 
under  false  pretences.  A  so-called  10  volume  solution  gives,  it  is 
true,  10  volumes  of  0  when  decomposed  gasometrically  with 
permanganate,  but  5  volumes  of  the  0  comes  from  the  per- 
manganate itself,  and  therefore  such  a  solution  is  really  only  5 
volume.  A  true  10  volume  solution  should  yield  from  itself  when 
fully  decomposed,  ten  times  its  volume  of  0,  and  contain  by  weight 
3-04  per  cent,  of  H202  or  1'43  per  cent,  by  weight  of  0. 

Kingzett  (J.  C.  S.  1880,  792)  has  clearly  shown  that  the  best 
and  most  rapid  estimation  of  the  hydrogen  peroxide,  contained  in 
any  given  solution  of  it,  is  made  by  iodine  and  thiosulphate  in  the 
presence  of  a  tolerably  large  excess  of  sulphuric  acid,  the  reaction 
being— 

2HI  +  H202=2H20  +  I2. 

The  function  performed  by  the  sulphuric  acid  is  difficult  of  ex- 
planation, but  the  want  of  uniformity  in  the  reaction  experienced  by 
many  operators  no  doubt  has  arisen  from  the  use  of  insufficient  acid. 

Kingzett's  method  consists  in  mixing  10  c.c.  of  the  peroxide 
solution  to  be  examined  with  about  30  c.c.  of  dilute  sulphuric 
acid  (1  :  2)  in  a  beaker,  adding  crystals  of  potassic  iodide  in 
sufficient  quantity,  and  after  standing  five  minutes  titrating  the 
liberated  iodine  with  -^  thiosulphate  and  starch.  The  peroxide 
solution  should  not  exceed  the  strength  of  2  volumes ;  if  stronger, 
it  must  be  diluted  proportionately  before  the  analysis. 


§  69.  PHOSPHORIC  ACID.  269 

In  the  case  of  a  very  weak  solution  it  will  be  advisable  to  titrate 
with  T^Q-  thiosulphate. 


1  c.c.  ^  thiosulphate  =  OOO  17  gm.  H202  or  O0016  gm.  0. 

The  estimation  of  this  substance  may  also  be  readily  made  in  the 
absence  of  organic  or  other  reducing  matters  by  weak  standard  per- 
manganate in  the  presence  of  free  sulphuric  acid,  the  permanganate 
being  added  until  a  faint  rose  colour  occurs  :  the  reaction  is  — 

2KMn04  +  5H202  +  3H2S04  =  K2S04  +  2MnS04  +  8H20  +  502. 

The  same  reaction  may  be  used  for  the  estimation  by  measuring 
the  oxygen  gas  evolved  in  a  suitable  apparatus,  such  as  the 
nitrometer. 

Carpenter  and  Nicholson  (Analyst,  ix.  36)  report  a  series 
of  experiments  on  the  analysis  of  hydrogen  peroxide,  both  by  the 
iodine  and  permanganate  methods. 

The  conclusion  they  arrive  at  is,  that  the  process  of  Kingzett 
is  accurate,  but  in  their  hands  somewhat  tedious,  owing  to  slow 
decomposition  towards  the  end.  Kingzett  however  states  that  if 
a  volume  of  strong  sulphuric  acid  equal  to  the  peroxide  taken  be  used, 
and  especially  if  the  dilute  solution  be  slightly  warmed,  the  reaction 
is  complete  in  a  few  minutes,  and  this  is  my  own  experience. 
Nevertheless,  for  technical  purposes,  very  good  results  may  be 
quickly  obtained,  either  by  natural  or  artificial  light,  with  simple 
titration  of  the  dilute  acidified  solution  by  —^  permanganate. 


PHOSPHORIC    ACID    AND    PHOSPHATES. 

P205=142. 

§  69.  THE  estimation  of  phosphoric  acid  volumetrically  may 
be  done  with  more  or  less  accuracy  by  a  variety  of  processes,  among 
which  may  be  mentioned  that  of  Mohr  as  lead  phosphate,  the 
indirect  method  as  silver  phosphate  (the  excess  of  silver  being  found 
by  thiocyanate),  by  standard  uranium  nitrate  or  acetate,  by 
Pemberton's  or  Schindler's  method  as  phospho-molybdate,  or 
when  existing  only  as  monocalcic  phosphate,  by  standard  alkali, 
as  recommended  by  Mollenda  or  Em  merlin  g.  Further,  there  is 
the  method  of  Stolba  by  separation  as  ammonio-magnesic  phosphate, 
and  the  titration  of  this  salt  when  obtained  pure  by  standard  acid. 
These  processes  are  mainly  useful  in  the  case  of  manures,  or  the  raw 
phosphates  from  which  manures  are  manufactured,  and  for  P205  in 
urine,  etc.  When,  however,  phosphorus  has  to  be  estimated  as  it 
exists  in  combination  with  metals  or  metallic  minerals,  it  is 
doubtful  whether  any  volumetric  method  can  be  relied  upon.  My 
experience  will  not  allow  the  recommendation  of  any  such  method. 
For  the  purpose  mentioned,  that  is  to  say,  when  in  combination 
with  alkaline  or  earthy  alkaline  bases  and  moderate  quantities  of 


270  VOLUMETRIC  ANALYSIS.  §    69. 

iron  or  alumina,  phosphoric  acid  may  be  estimated  volumetrically 
with  very  fair  accuracy,  and  with  much  greater  rapidity  than  by 
gravimetric  means  as  usually  carried  out.  This  remark,  however, 
can  only  be  applied  to  uranium  or  molybdenum  methods,  and  the 
alkalimetric  method  of  Stolba;  therefore  only  these  will  be 
described. 


1.     Separation   of  the   Phosphoric   Acid  previous   to   Titration. 

Natural  phosphates  used  for  the  manufacture  of  manures  differ 
materially  in  their  composition,  and  must  be  treated  differently  in 
their  analysis.  Many  of  the  rock  phosphates  contain  silica  in  large 
quantity,  and  of  such  a  nature  that  hydrochloric  acid  readily 
dissolves  a  portion  of  the  silica.  This  must  be  separated  by 
evaporating  the  acid  solution  to  dryness,  heating  to  150°  or  so,  and 
redissolving  the  phosphate  in  dilute  HC1  or  HNO3,  and  filtering  off 
the  gelatinous  SiO2.  If  this  is  not  done,  subsequent  precipitation 
either  by  molybdenum  or  magnesia  will  be  rendered  inaccurate 
from  the  presence  of  SiO2. 

In  the  case  of  separation  by  molybdenum,  organic  matter  must  be 
previously  destroyed  by  calcination.  Chlorides,  if  present,  should 
also  be  removed  by  repeated  evaporation  with  HNO3,  inasmuch  as 
the  phospho-molybdate  is  sensibly  soluble  in  free  HC1,  or  in 
alkaline  or  ferric  chlorides  in  the  presence  of  nitric  acid.  Free 
sulphuric  acid  also  retards  the  formation  of  the  precipitate,  but  neutral 
sulphates  are  of  no  consequence.  Nitric  acid,  therefore,  must  be 
the  final  solvent  in  all  cases  where  this  method  of  separation  is  used. 
Fluorides  are  of  no  consequence,  as  they  are  not  decomposed  by 
this  acid. 

In  the  case  of  separation  direct  by  magnesia,  hydrochloric  acid 
is  the  usual  solvent ;  but  soluble  silica  must  always  be  removed  by 
evaporation  previous  to  precipitation,  especially  for  the  gravimetric 
method. 

Many  natural  guanos  contain  only  mere  traces  of  SiO2,  also 
some  mineral  phosphates  like  the  Belgian  phosphatic  sands.  Bones 
and  similar  organic  phosphates  are  in  like  manner  almost  entirely 
free  from  it,  and  the  same  is  the  case  with  many  superphosphates. 

These  substances  may  therefore,  although  contaminated  with 
iron  and  alumina,  be  directly  treated  with  magnesic  citrate  as 
described  further  on. 

It  will  be  evident  to  most  operators  of  any  experience,  that  if  the 
uranium  method  is  capable  of  accurate  volumetric  results  by  special 
precautions,  the  complete  purity  of  the  precipitate  either  in  the  case 
of  magnesia  or  molybdenum  is  not  a  matter  of  great  importance. 
This  is  true  to  some  extent,  but  it  is  always  advisable  to  have  the 
P205  in  as  clean  a  form  as  possible,  and  especially  is  this  necessary 
in  the  citro-uranic  method,  since  the  smallest  trace  of  citric  acid 
interferes  seriously  with  the  colour  reaction. 


§  G9.  PHOSPHORIC  ACID.  271 

For  many  years  past  I  have  used  very  extensively  the  magnesic 
citrate  method  of  analysis  direct  by  weight,  and  with  the  most 
satisfactory  results  compared  with  the  molybdic  method  of  separa- 
tion. For  superphosphates  where  iron  or  alumina  is  present,  or 
even  raw  phosphatic  materials  containing  these  substances,  nothing 
better  can  be  desired  for  rapidity,  cleanliness,  and  accuracy.  There 
are  instances  in  which  reprecipitation  is  necessary  to  purify  from 
large  excesses  of  Fe,  Al,  Ca,  etc.;  but  these  are  comparatively  rare; 
and  even  then  less  trouble  is  involved  than  by  molybdenum,  unless 
the  modern  method  of  rapid  separation  in  the  presence  of  a  large 
excess  of  ammonic  nitrate,  with  a  small  excess  of  nitric  acid,  be 
adopted,  as  in  Pemberton's  volumetric  method.  This  is  available 
in  many  cases,  and  is  much  more  cleanly  than  when  concentrated 
nitric  acid  is  present,  and  the  precipitate  washed  with  the  molybdic 
solution  itself. 

Citro-Ma&nesic  Solution. — 27  gm.  of  pure  magnesic  carbonate 
are  added  by  degrees  to  a  solution  of  270  gm.  of  citric  acid  in 
350  c.c.  of  warm  water;  when  all  effervescence  is  over  and  the 
liquid  cool,  about  400  c.c.  of  solution  of  ammonia  are  added, 
containing  10  per  cent,  of  ]SrH3  (about  0'96  sp.  gr.),  or  if  other 
strength  is  used,  enough  to  ensure  decided  excess  of  NH3 : 
the  whole  is  then  diluted  to  a  liter,  and  preserved  in  a  well- 
stoppered  bottle.  20  c.c.  of  this  solution  is  sufficient  to  insure 
the  precipitation  of  O'l  gm.  of  P205  in  the  presence  of  a  large 
excess  of  NH3,  unless  accompanied  by  excessive  quantities  of  Fe 
or  Al,  which  may  be  known  by  an  immediate  precipitate  being 
formed  on  its  being  mixed  with  the  phosphate  solution  and  ammonia. 
In  this  case  a  fresh  portion  of  the  phosphate  must  be  taken,  and 
30  or  40  c.c.  of  the  magnesia  solution  used. 

For  estimation  by  weight,  it  is  not  advisable  to  take  more 
phosphate  solution  than  corresponds  to  O'l  gm.  P205,  using  20  or 
40  c.c.  of  magnesia  solution,  and  a  considerable  excess  of  10  per 
cent,  ammonia. 

For  volumetric  purposes  the  same  quantities  may  be  taken. 
The  precipitation  is  much  hastened  by  cooling  the  liquid  to  12°  C. 
or  50°  F.,  accompanied  by  rapid  stirring.  This,  however,  causes  a 
demise  crystalline  deposit  on  the  sides  of  the  beaker  and  on  the  rod, 
which  is  difficult  to  remove  if  required  to  be  weighed.  But  if 
it  has  to  be  estimated  volumetrically  this  is  of  no  consequence,  as 
the  titration  may  take  place  in  the  same  beaker  and  with  the  same 
rod,  after  they  have  been  well  washed  with  weak  ammonia,  the 
washing  being  passed  through  the  filter  containing  the  main 
precipitate. 

The  precipitate  of  ammonio-magnesic  phosphate  formed  is  dense, 
crystalline,  and  admits  of  very  easy  washing,  and  the  use  of  very  free 
filtering  paper.  It  is  washed  with  2J  per  cent,  ammonia  until  no 
ammonic  citrate  or  magnesia  is  present  in  the  filtrate,  then  either 


272  VOLUMETKIC   ANALYSIS.  §    69. 

dried  for  ignition  and  weighed  as  Mg2P207,  or  dissolved  through 
the  filter  with  dilute  nitric  or  hydrochloric  acid  for  subsequent 
titration  with  uranium. 

It  is  advisable  in  all  cases  to  have  the  acids  and  ammonia  of  a 
tolerably  uniform  strength,  and  to  use  as  nearly  as  possible  the  same 
proportions  in  the  analysis.  Convenient  strengths  are  10  per  cent. 
^N~H3  for  rendering  the  phosphate  and  citrate  mixture  alkaline, 
also  for  neutralizing  the  free  acid  in  superphosphates,  and  2J  per 
cent,  for  washing  the  precipitate  ;  10  per  cent,  nitric  or  hydrochloric 
acid  for  dissolving  the  precipitate  for  titration.  This  is  far  better 
than  pouring  in  acids  or  alkalies  at  random. 

Molybdenum  Solution. — This  is  the  usual  solution  made  by 
dissolving  150  gm.  of  ammonic  molybdate  in  a  liter  of  water,  and 
pouring  it  into  a  liter  of  nitric  acid  sp.  gr.  1  *20. 

50  c.c.  of  this  solution  suffices  amply  to  precipitate  O'l  gm.  P205, 
and  it  should  be  accompanied  by  a  quantity  of  ammonic  nitrate  in 
clear  solution  equal  to  about  15  per  cent,  of  the  total  weight  of 
liquid.  If  heated  to  80°  or  90°  C.,  the  precipitation  is  complete  in 
one  hour.  Instead  of  as  formerly  washing  the  precipitate  with  equal 
parts  of  molybdic  solution  and  water,  a  10  per-cent.  solution  of 
ammonic  nitrate  is  used. 

The  precipitate  of  yellow  phospho-molybdate  is  dissolved  in  2J 
per  cent,  ammonia  solution  through  the  filter,  taking  care  that  every 
trace  is  removed  from  its  folds,  and  then  the  usual  magnesia  mixture 
added  "drop wise"  with  gentle  stirring  in  the  proportion  of  not  less 
than  15  c.c.  for  every  O'l  gm.  P205.  Two  hours  amply  suffice  for 
this  precipitate  to  separate ;  it  is  then  filtered  and  washed  with  2  J 
per  cent.  NH3  till  clean,  when  it  may  be  either  ignited  as  Mg2P207, 
or  titrated  with  uranium. 

Magnesia  Mixture. — 55  gm.  of  crystallized  magnesic  chloride 
and  70  gm.  of  ammonic  chloride  are  dissolved  to  a  liter  with 
2J  per  cent,  ammonic  hydrate.  10  c.c.  is  sufficient  to  precipitate 
0*1  gm.  P205,  but  it  is  safer  to  use  15  c.c.  as  before  recom- 
mended. 

The  literature  connected  with  the  determination  of  phosphoric 
acid  is  very  voluminous,  and  many  competent  chemists  have  con- 
tributed thereto  in  various  scientific  journals  and  standard  works, 
which  have  been  consulted  and  freely  used  in  the  compilation  of 
this  section.  * 

*Fresenius,  Quant,.  Chem.  Analyse,  6*e  Aufl.  411. 
Abesser,  Jani  u.  Marcker,  Z.  a.  C.  xii.  239. 
Schumann,  ibid.  xi.  382;  Janovsky,  ibid.  xi.  153. 
Gilbert,  ibid.  xii.  1 ;  Kumpler.  ibid.  xii.  151. 
Fresenius,  Neubauer,  and  Luck.  ibid.  ix.  16. 
Mohr,  Titrirbucfc,  4te  Aufl.  520. 
Neubauer,  Anal,  des  Harris,  6te  Aufl. 

Joulie,  Moniteur  Scientifique,  1872—3,  et  Annuaire  de  la  Pharmacie,  redige  par 
Dr .  C .  Mehu,  1875,  465,  etc.,  etc.    Joulie,  Ann.  Agronom.  xi.  97—129. 


§    69.  PHOSPHORIC    ACID.  273 

2.    Precipitation  as  TTranic  Phosphate  in  Acetic  Acid  Solution. 

This  method  is  based  on  the  fact  that  when  uranic  acetate  or 
nitrate  is  added  to  a  neutral  solution  of  tribasic  phosphoric  acid, 
such,  for  instance,  as  sodic  orthophosphate,  the  whole  of  the 
phosphoric  acid  is  thrown  down  as  yellow  uranic  phosphate  Ur203, 
P205  +  Aq.  Should  the  solution,  however,  contain  free  mineral 
acid,  it  must  be  neutralized  with  an  alkali,  and  an  alkaline  acetate 
added,  together  with  excess  of  free  acetic  acid.  In  case  of  using 
ammonia  and  ammonic  acetate,  the  whole  of  the  phosphoric  acid 
is  thrown  down  as  double  phosphate  of  uranium  and  ammonia, 
having  a  light  lemon  colour,  and  the  composition  Ur203, 
2(NH40),  P205  +  Aq.  When  this  precipitate  is  washed  with  hot 
water,  dried  and  burned,  the  ammonia  is  entirely  dissipated  leaving 
uranic  phosphate,  which  possesses  the  formula  Ur203,  P205,  and 
contains  in  100  parts  80*09  uranic  oxide  and  19 '91  phosphoric 
acid.  In  the  presence  of  fixed  alkalies,  instead  of  ammonia,  the 
precipitate  consists  simply  of  uranic  phosphate.  By  this  method 
phosphoric  acid  may  be  completely  removed  from  all  the  alkalies 
and  alkaline  earths ;  also,  with  a  slight  modification,  from  iron ; 
not,  however,  satisfactorily  from  alumina  when  present  in  any 
quantity. 

The  details  of  the  gravimetric  process  were  fully  described  by 
me  (C.  N.  i.  97 — 122),  and  immediately  after  the  publication  of 
that  article,  while  employed  in  further  investigation  of  the  subject, 
I  devised  the  volumetric  method  now  to  be  described.  Since  that 
time  it  has  come  to  my  knowledge  that  Xeubauer*  and  Pincusf 
had  independently  of  each  other  and  myself  arrived  at  the  same 
process.  This  is  not  to  be  wondered  at,  if  it  be  considered  how 
easy  the  step  is  from  the  ordinary  determination  by  weight  to  that 
by  measure,  when  the  delicate  reaction  between  uranium  and 
potassic  ferrocyanide  is  known.  Moreover,  the  great  want  of  a 
really  good  volumetric  process  for  phosphoric  acid  in  place  of  those 
hitherto  used  has  been  felt  by  all  who  have  anything  to  do  with  it, 
and  consequently  the  most  would  be  made  of  any  new  method 
possessing  so  great  a  claim  to  accuracy  as  the  gravimetric  estimation 
of  phosphoric  acid  by  uranium  undoubtedly  does. 

Conditions  under  -which  accuracy  may  be  insured. — Objections 
have  been  urged,  not  without  reason,  that  this  process  is  inaccurate, 
because  varying  amounts  of  saline  substances  have  an  influence 
upon  the  production  of  colour  with  the  indicator.  J  Again,  that 
very  different  shades  of  colour  occur  with  lapse  of  time.  This 

*  Archiv.  filr  wissenscMftliche  Heilkunde,  iv.  228. 
t  Journal  fiir  Prakt.  CJiem.  Ixxvi.  104. 

JMalot  prefers  to  make  use  of  the  reaction  which  occurs  between  cochineal  and 
uranium,  which  gives  a  bluish-green  lake,  as  the  indicator.  With  perfectly  pure 
materials  this  method  succeeds,  but  where  traces  of  iron,  alumina,  or  other  matters 
occur,  the  end-reaction  is  far  less  delicate  than  with  the  ferrocyanide. 

T 


274  VOLUMETRIC   ANALYSIS.  §    69. 

is  all  true,  and  the  analysis  is  unfortunately  one  of  that  class  which 
requires  uniform  conditions ;  but  when  the  source  of  irregularity  is 
known,  it  is  not  difficult  to  obviate  them.  Therefore  it  is  absolutely 
essential  that  the  standardizing  of  the  uranium  solution  should  be 
done  under  the  same  conditions  as  the  analysis.  For  instance,  a 
different  volume  of  uranium  will  be  required  to  give  the  colour  in 
the  presence  of  salts  of  ammonia  to  that  which  would  be  necessary 
with  salts  of  the  fixed  alkalies  or  alkaline  earths.  But  if  the 
standard  solution  is  purposely  adjusted  with  ammonia  salts  in  about 
the  same  proportion,  the  difficulties  all  vanish.  Fortunately  this 
can  be  easily  done,  and  as  the  chief  substances  requiring  analysis 
are  more  or  less  ammoniacal  in  their  composition,  such  as  urine, 
manures,  etc.,  110  practical  difficulty  need  occur. 

Excessive  quantities  of  alkaline  or  earthy  salts  modify  the  colour, 
but  especially  is  it  so  with  acetate  or  citrate  of  ammonia.  For  this 
reason  I  have  insisted  on  the  complete  washing  of  the  citro- 
magnesian  precipitate,  where  that  method  of  separating  P205  is 
adopted  previous  to  titration. 


3.     Estimation  of  Phosphoric   Acid  in  combination  -with   Alkaline 
Bases,  or  in  presence  of  small  quantities  of  Alkaline  Earths. 

The  necessary  materials  are — 

(a)  A  standard  solution  of  Uranium.  1  c.c.  =0'005  gm.  P205. 

(b)  A  standard  solution  of  tribasic  Phosphoric  acid. 

(c)  A  solution  of  Sodic  acetate  in  dilute  acetic  acid,  made  by 
dissolving  100  gm.  of  sodic  acetate  in  water,  adding  50  c.c.   of 
glacial  acetic  acid,  and  diluting  to  1  liter.     Exact  quantities  are 
not  necessary. 

(d)  A    freshly  prepared  solution  of   Potassic  ferrocyanide,  or 
some  finely  powdered  pure  crystals  of  the  same  salt. 

Standard  Solution  of  Uranium. — This  solution  may  consist 
either  of  uranic  nitrate  or  acetate.  An  approximate  solution  is 
obtained  by  using  about  35  gm.  of  either  salt  to  the  liter. 
In  using  uranic  nitrate  it  is  imperative  that  the  sodic  acetate 
should  be  added  in  order  to  avoid  the  possible  occurrence 
of  free  nitric  acid  in  the  solution.  With  acetate,  however, 
it  may  be  omitted  at  the  discretion  of  the  operator,  but  it  is 
important  that  the  method  used  in  standardizing  the  uranium  be 
invariably  adhered  to  in  the  actual  analysis.  The  solution  should 
be  perfectly  clear  and  free  from  basic  salt.  Whether  made  from 
acetate  or  nitrate,  it  is  advisable  to  include  about  25  c.c.  of  pure 
glacial  acetic,  or  a  corresponding  quantity  of  weaker  acid  to 
each  liter  of  solution;  exposure  to  light  has  then  less  reducing 
action. 

My  own  practice  is  to  use  in  all  cases  acetate  solution,  and 
dispense  entirely  with  the  addition  of  sodic  acetate. 


§    69.  PHOSPHOKIC  ACID.  275 

4.      Titration    of   the    TTranium    Solution. 

Standard  Phosphoric  Acid. — When  the  uranium  solution  is  not 
required  for  phosphate  of  lime,  it  may  be  titrated  upon  ammonio- 
sodic  phosphate  (microcosmic  salt)  as  follows : — 5*886  gm.  of  the 
crystallized,  non-effloresced  salt  (previously  powdered  and  pressed 
between  bibulous  paper  to  remove  any  adhering  moisture)  are 
weighed,  dissolved  in  water,  and  diluted  to  1  liter.  50  c.c.  of  this 
solution  will  represent  0*1  gm.  P205.* 

50  c.c.  of  this  solution  are  measured  into  a  small  beaker,  5  c.c.  sodic  acetate 
solution  added  if  uranic  nitrate  is  to  be  used,  and  the  mixture  heated  to 
90°  or  100°  C.  The  uranium  solution  is  then  delivered  in  from  a  burette, 
divided  into  ^  c.c.,  until  a  test  taken  shall  show  the  slight  predominance  of 
uranium.  This  is  done  by  spreading  a  drop  or  two  of  the  hot  mixture  upon 
a  clean  white  level  plate,  and  bringing  in  contact  with  the  middle  of  the  drop 
a  small  glass  rod  moistened  with  the  freshly  made  solution  of  ferrocyanide, 
or  a  dust  of  the  powdered  salt.  The  occurrence  of  a  faint  brown  tinge  shows 
an  excess  of  uranium,  the  slightest  amount  of  which  produces  a  brown 
precipitate  of  uranic  ferrocyanide. 

A  second  or  third  titration  is  then  made  in  the  same  way,  so  as 
to  arrive  exactly  at  the  strength  of  the  uranium  solution,  which 
is  then  diluted  and  re-titrated,  until  exactly  20  c.c.  are  required  to 
produce  the  necessary  reaction  with  50  c.c.  of  phosphate. 

Suppose  18*7  c.c.  of  the  uranium  solution  have  been  required  to 
produce  the  colour  with  50  c.c.  of  phosphate  solution,  then  every 
18 '7  c.c.  will  have  to  be  diluted  to  20  c.c.  in  order  to  be  of  the 
proper  strength,  or  935  to  1000.  After  dilution,  two  or  three 
fresh  trials  must  be  made  to  insure  accuracy. 

It  is  of  considerable  importance  that  the  actual  experiment  for 
estimating  phosphoric  acid  by  means  of  the  uranium  solution 
should  take  place  with  about  the  same  bulk  of  fluid  that  has  been 
used  in  standardizing  the  solution,  and  with  as  nearly  as  possible 
the  same  relative  amount  of  sodic  acetate,  and  the  production  of 
the  same  depth  of  colour  in  testing.  Hence  the  proportions  here 
recommended  have  been  chosen,  so  that  50  c.c.  of  liquid  shall 
contain  O'l  gm.  P205. 

Standard  Phosphoric  Acid  corresponding-  volume  for  volume  with 
Standard  Uranium. — This  solution  is  obtained  by  dissolving 
14 '7 15  gm.  of  microcosmic  salt  in  a  liter,  and  is  two  and  a  half 
times  the  strength  of  the  solution  before  described ;  it  is  used  for 
residual  titration  in  case  the  required  volume  of  uranium  is  over- 
stepped in  any  given  analysis. 

A  little  practice  enables  the  operator  to  tell  very  quickly  the 

*  "W.  B.  Giles,  who  has  had  great  experience  in  the  determination  of  phosphoric  acid 
in  various  forms,  has  called  my  attention  to  dihydric  potassic  phosphate,  KH^PO4,  as  an 
excellent  form  of  salt  for  a  standard  solution.  The  sample  sent  to  me  was  in  beautifully 
formed  crystals  which  do  not  alter  on  exposure  to  the  air,  and  makes  a  solution  which 
keeps  clear.  Everyone  knows  how  unsatisfactory  sodic  phosphate  is,  hoth  as  to  its 
state  of  hydration  and  its  keeping  qualities  in  solution :  the  microcosmic  salt  is  better, 
but  is  open  to  objection  on  the  score  of  indefinite  hydration.  If  the  potassium  salt  is 
used,  a  standard  solution  of  the  proper  strength  is  made  by  dissolving  3'83  gm.  in  a  liter 

T    2 


276:  VOLUMETRIC   ANALYSIS.  §    69. 

precise  point ;  but  it  must  be  remembered  that  when  the  two  drops 
are  brought  together  for  the  production  of  the  chocolate  colour, 
however  faint  it  seems  at  first,  owing  to  the  retarding  action  of  the 
sodic  acetate  and  acetic  acid  upon  the  formation  of  uranic 
ferrocyanide,  if  left  for  some  little  time  the  colour  increases  con- 
siderably ;  but  this  has  no  effect  upon  the  accuracy  of  the  process, 
since  the  original  standard  of  the  solution  has  been  based  on  an. 
experiment  conducted  in  precisely  the  same  way. 

The  Analysis :  In  estimating  unknown  qualities  of  P2O5,  it  is  necessary 
to  have  an  approximate  knowledge  of  the  amount  in  any  given  material,  so 
as  to  fulfil  as  nearly  as  possible  the  conditions  laid  down  above ;  that  is  to  say, 
50  c.c.  of  solution  shall  contain  about  O'l  gm.  P2O5,  or  whatever  other  pro- 
portion may  have  been  used  in  standardizing  the  uranium. 

The  compound  containing  the  P2O5  to  be  estimated  is  dissolved  in  water ; 
if  no  ammonia  is  present,  1  c.c.  of  10  per  cent,  solution  is  dropped  in  and 
neutralized  with  the  least  possible  quantity  of  acetic  acid  (also  5  c.c.  of  sodic 
acetate  if  uranic  nitrate  has  to  be  used),  and  the  volume  made  up  to  about 
50  c.c.,  then  heated  to  about  90°  C.  on  the  water  bath,  and  the  uranium 
solution  delivered  in  cautiously,  with  frequent  testing  as  above  described, 
until  the  faint  brown  tinge  appears. 

The  first  trial  will  give  roughly  the  amount  of  solution  required,  and 
taking  that  as  a  guide,  the  operator  can  vary  the  amount  of  liquid  and  sodic 
acetate  for  the  final  titration,  should  the  proportions  be  found  widely 
differing  from  those  under  which  the  strength  of  the  uranium  was  originally 
fixed. 

Each  c.c.  of  uranium  solution  =0  005  gm.  P2O5. 

5.  Estimation  of  Phosphoric  Acid  in  combination  with  Lime  and 
Mag-nesia  (Bones,  Bone  Ash,  Soluble  Phosphates,  and  other 
Phosphatic  Materials,  free  from  Iron  and  Alumina). 

The  procedure  in  these  cases  differs  from  the  foregoing  in  two 
respects  only ;  that  is  to  say,  the  uranium  solution  is  preferably 
standardized  by  tribasic  calcic  phosphate;  and  in  the  process  of 
titration  it  is  necessary  to  add  nearly  the  full  amount  of  uranium 
required  before  heating  the  mixture,  so  as  to  prevent  the  precipita- 
tion of  calcic  phosphate,  which  is  apt  to  occur  in  acetic  acid 
solution  when  heated;  or  the  modification  adopted  by  Fresenius, 
Xeubauer,  and  Luck,  may  be  used,  which  consists  in  reversing 
the  process  by  taking  a  measured  volume  of  uranium,  and  delivering 
into  it  the  solution  of  phosphate  until  a  drop  of  the  mixture  ceases 
to  give  a  brown  colour  with  ferrocyanide.  This  plan  gives,  how- 
ever, much  more  trouble,  and  possesses  no  advantage  on  the  score 
of  accuracy,  because  in  any  case  at  least  two  titrations  must  occur,  and 
the  first  being  made  somewhat  roughly,  in  the  ordinary  way,  shows 
within  1  or  2  c.c.  the  volume  of  standard  uranium  required  :  and  in 
the  final  trial  it  is  only  necessary  to  add  at  once  nearly  the  quantity, 
then  heat  the  mixture,  and  finish  the  titration  by  adding  a  drop  or 
two  of  uranium  at  a  time  until  the  required  colour  is  obtained. 

This  reversed  process  is  strongly  advocated  by  many  operators, 
but  except  in  rare  instances  I  fail  to  see  its  superiority  to  the  direct 


§    69.  ,      PHOSPHORIC    ACID.  277 

method  for  general  use.  The  best  modification  to  adopt  in  the 
reverse  process  is  to  use  invariably  an  excess  of  uranium,  and  to 
titrate  back  with  standard  phosphate  solution  till  the  colour 
disappears ;  this  avoids  all  the  trouble  of  preparing  and  cleaning  a 
burette  for  the  solution  to  be  analyzed,  and  if  a  standard  phosphate 
is  made  to  correspond  volume  for  volume  with  the  uranium,  an 
-analysis  may  always  be  brought  into  order  at  any  stage. 

Standard  Calcic  Phosphate. — It  is  not  safe  to  depend  upon  the 
usual  preparations  of  tricalcic  phosphate  by  weighing  any  given 
quantity  direct,  owing  to  uncertainty  as  to  the  state  in  which  the 
phosphoric  acid  may  exist;  therefore,  in  order  to  titrate  the 
uranium  solution  with  calcic  phosphate,  it  is  only  necessary  to 
take  rather  more  than  5  gm.  of  precipitated  pure  tricalcic  phosphate 
such  as  occurs  in  commerce,  dissolve  it  in  a  slight  excess  of  dilute 
hydrochloric  acid,  precipitate  again  with  a  slight  excess  of  ammonia, 
re-dissolve  in  a  moderate  excess  of  acetic  acid,  then  dilute  to 
a  liter;  by  this  means  is  obtained  a  solution  of  acid  moiiocalcic 
phosphate,  existing  under  the  same  conditions  as  occur  in  the 
actual  analysis.  In  order  to  ascertain  the  exact  amount  of  tribasic 
phosphoric  acid  present  in  a  given  measure  of  this  solution,  two 
portions  of  50  c.c.  each  are  placed  in  two  beakers,  each  holding  about 
half  a  liter.  A  slight  excess  of  solution  of  uranic  acetate  or  nitrate 
is  then  added  to  each,  together  with  about  10  c.c.  of  the  acetic 
solution  of  sodic  acetate ;  they  are  then  heated  to  actual  boiling  on 
a,  hot-plate  or  sand-bath,  the  beakers  filled  up  with  boiling  distilled 
water,  and  then  set  aside  to  settle,  which  occurs  very  speedily.  The 
supernatant  fluid  should  be  faintly  yellow  from  excess  of  uranium. 
When  perfectly  settled,  the  clear  liquid  is  withdrawn  by  a  syphon 
or  poured  off  as  closely  as  possible  without  disturbing  the 
precipitate,  and  the  beakers  again  filled  up  with  boiling  water. 
The  same  should  be  done  a  third  time,  when  the  precipitates 
may  be  brought  on  two  filters,  and  need  very  little  further 
washing. 

When  the  filtration  is  complete,  the  filters  are  dried  and  ignited 
separate  from  the  precipitate,  taking  care  to  burn  off  all  carbon. 
Before  being  weighed,  however,  the  uranic-phosphate  must  be 
moistened  with  strong  nitric  acid,  dried  perfectly  in  the  water  bath 
or  oven,  and  again  ignited ;  at  first,  very  gently,  then  strongly,  so 
as  to  leave  a  residue  when  cold  of  a  pure  light  lemon  colour.  This 
is  uranic  phosphate  Ur203,  P205,  the  percentage  composition  of 
which  is  80 '09  of  uranic  oxide,  and  19*91  of  phosphoric  acid. 

The  two  precipitates  are  accurately  weighed,  and  should  agree  to 
within  a  trifle.  If  they  differ,  the  mean  is  taken  to  represent  the 
amount  of  P205  in  the  given  quantity  of  tricalcic  phosphate,  from 
which  may  be  calculated  the  strength  of  the  solution  to  be  used  as 
a  standard.  Of  course  any  other  accurate  method  of  determining 
the  P205  may  be  used  in  place  of  this. 


278  VOLUMETRIC  ANALYSIS.  §    69. 

The  actual  standard  required  is  5  gin.  of  pure  tricalcic  phosphate 
per  liter ;  and  it  should  be  adjusted  to  this  strength  by  dilution, 
after  the  actual  strength  has  been  found.  In  this  way  is  obtained 
a  standard  which  agrees  exactly  with  the  analysis  of  a  super- 
phosphate or  other  similar  manure. 

Standard  Uranium  Solution. — This  is  best  adjusted  to  such 
strength  that  25  c.c.  are  required  to  give  the  faint  chocolate  colour 
with  ferrocyanide,  when  50  c.c.  of  the  standard  acetic  solution  of 
calcic  phosphate  are  taken  for  titration.  Working  in  this  manner 
each  c.c.  of  uranium  solution  represents  1  per  cent,  of  soluble 
tricalcic  phosphate,  when  1  gm.  of  manure  is  taken  for  analysis, 
because  50  c.c.  of  the  calcic  phosphate  will  contain  monocalcic 
phosphate  equal  to  0'25  gm.  of  Ca3P208  and  will  require  25  c.c.  of 
uranium  solution  to  balance  it. 

These  standards  are  given  as  convenient  for  manures,  but  they 
may  be  modified  to  suit  any  particular  purpose. 

The  Analysis  in  case  of  Superphosphate  free  from  Fe  and  Al,  except 
in  mere  traces : — 10  gm.  of  the  substance  is  weighed,  placed  in  a  small  glass 
mortar  and  gently  broken  down  by  the  pestle,  cold  water  being  used  to  bring- 
it  to  a  smooth  cream.  The  material  should  not  be  ground  or  rubbed  hard, 
which  might  cause  the  solution  of  some  insoluble  phosphate  in  the 
concentrated  mixture.  The  creamy  substance  is  washed  gradually  without 
loss  into  a  measuring  flask  marked  at  503'5  c.c.,  the  3'5  c.c.  being  the  space 
occupied  by  the  insoluble  matters  in  an  ordinary  25  to  30  per  cent, 
superphosphate.  The  flask  is  filled  to  the  mark  with  cold  water,  and  shaken 
every  few  minutes  during  about  half-an-hour.  A  portion  is  then  filtered 
through  a  dry  filter  into  a  dry  beaker,  and  50  c.c.  =  l  gm.  of  manure 
measured  into  a  beaker  holding  about  100  c.c.  Sufficient  10  per  cent,  ammonia 
is  then  added  to  precipitate  the  monocalcic  phosphate  in  the  form  of 
Ca3P2O8  (in  all  ordinary  superphosphates  there  is  enough  Ca  present  as 
sulphate  to  ensure  this,  and  four  or  five  drops  of  ammonia  generally  suffice 
to  effect  the  precipitation).  Acetic  acid  is  then  added  in  just  sufficient 
quantity  to  render  the  liquid  clear.  Should  traces  of  gelatinous  A1PO4  or 
FePO4  occur  at  this  stage,  the  liquid  will  be  slightly  opalescent ;  but  this 
may  be  disregarded  if  only  slight,  as  the  subsequent  heating  will  enable  the 
uranium  to  decompose  it.  If  more  than  traces  occur,  the  method  will  not  be 
accurate,  and  recourse  must  be  had  to  separation  by  the  citro-magnesic 
solution. 

While  the  liquid  is  still  cold,  a  measured  volume  of  the  standard  uranium 
is  run  in  with  stirring,  and  occasional  drops  are  taken  out  with  a  glass  rod, 
and  put  in  contact  with  some  ferrocyanide  indicator  sprinkled  on  a  white  plate 
until  a  -faint  colour  occurs.  The  beaker  is  then  placed  in  the  water-bath  for 
a  few  minutes,  and  again  the  mixture  tested  with  the  indicator :  after  heating 
in  this  way  the  testing  ought  to  show  no  colour.  More  uranium  is  then 
added  with  stirring,  and  drop  by  drop  till  the  proper  reaction  occurs.  This 
titration  is  only  a  guide  for  a  second,  which  may  be  made  more  accurate  by 
running  in  at  once  very  nearly  the  requisite  volume  of  uranium. 

This  operation  may  be  reversed,  if  so  desired,  by  making  the  clear 
solution  of  phosphate  up  to  a  definite  volume  (say  60  c.c.),  and 
running  it  into  a  measured  volume  of  uranium  until  a  test  taken 
shows  no  colour. 


§    69.  PHOSPHORIC   ACID.  279 

6.    Estimation  of  Phosphoric  Acid  in  Minerals  or  other  substances 
containing-  Iron,  Alumina,  or  other  disturbing-  matters. 

In  order  to  make  use  of  any  volumetric  process  for  this  purpose, 
the  phosphoric  acid  must  be  separated.  As  has  been  already 
described,  this  may  be  done  either  by  the  molybdic  precipitation 
followed  by  solution  in  !NH3,  again  precipitated  with  ordinary 
magnesia  mixture,  or  direct  separation  by  citro-magnesia  mixture. 
In  either  case  the  ammonio-magnesic  salt  is  dissolved  in  the  least 
possible  quantity  of  nitric  or  hydrochloric  acid,  neutralized  with 
ammonia,  acidified  with  acetic  acid,  and  the  titration  with  uranium 
carried  out  as  before  described. 

7.     Joulie's  Method. 

This  differs  somewhat  from  the  foregoing,  and  may  be  summarized 
as  follows  (Munro,  C.  N.  lii.  85). 

Joulie  applies  the  citro-magnesia  method  to  all  phosphates, 
Avhether  containing  iron  and  alumina  or  not,  and  prefers  nitrate  to 
acetate  of  uranium. 

1  to  10  gm.  of  the  sample  are  dissolved  in  HC1.  Some  chemists  use 
nitric  acid  with  a  view  of  leaving  as  much  ferric  oxide  as  possible  undissolved. 
This  course  is  condemned  by  the  author,  because  the  presence  of  ferric  salts 
in  no  way  interferes  with  the  process,  and  because  HC1  is  a  much  better 
solvent  of  mineral  phosphates  than  nitric  acid,  and  leaves  a  residue  free  from 
iron,  by  the  whiteness  of  which  one  may  judge  of  the  completeness  of  the 
attack.  In  the  case  of  phosphates  containing  a  little  pyrites,  nitric  acid 
should  be  used  in  conjunction  with  hydrochloric.  The  removal  of  silica  by 
evaporation  to  dryness  is  necessary  only  in  those  cases  where  the  sample 
contains  silicates  decomposable  by  HC1,  with  separation  of  gelatinous  silica. 
The  sample  is  boiled  with  the  acid  in  a  measuring  flask  until  the  residue  is 
perfectly  white,  the  contents  are  cooled,  made  up  to  the  mark  with  cold 
water,  mixed,  filtered  through  a  dry  filter,  and  such  a  fraction  of  the  filtrate 
withdrawn  by  a  pipette  as  contains  about  50  m.gm.  of  P2O5.  The  sample 
being  delivered  from  the  pipette  into  a  small  beaker,  10  c.c.  of  citro-magnesia 
solution  are  added,  and  then  a  large  excess  of  ammonia.  If  this  quantity 
of  citro-magnesia  liquor  is  sufficient,  no  precipitate  will  form  until  the  lapse 
of  a  few  moments;  should  an  immediate  precipitate  form,  it  is  iron  or 
aluminium  phosphate.  In  this  case  a  fresh  sample  must  be  pipetted  off,  and 
20  c.c.  citro-magnesia  liquor  added ;  it  is  of  no  use  adding  another  10  c.c.  of 
the  citric  solution  to  the  original  sample,  as  the  precipitated  phosphates  of 
iron  and  aluminium  do  not  readily  redissolve  when  once  formed.  The  citro- 
magnesia  liquor  is  the  same  as  described  on  p.  271.  The  old  plan  of  adding 
first  citric  acid  and  then  "  magnesia  mixture  "  to  the  solution  under,  analysis 
frequently  leads  to  incomplete  precipitation  of  the  phosphoric  acid,  because 
the  ammonio-magnesic  phosphate  is  slightly  soluble  in  ammonic  citrate 
unless  a  sufficient  excess  of  magnesium  salt  is  present,  and  therefore  the 
quantity  of  magnesium  salt  should  be  increased  pari  passu  with  the  citric 
acid  required,  which  is  best  done  when  they  are  in  solution  together.  The 
liquid  after  precipitation  is  allowed  to  stand  from  2  to  12  hours  (covered  to 
prevent  evaporation  of  ammonia),  and  then  decanted  through  a  small  filter. 
The  precipitate  remaining  in  the  beaker  is  washed  with  weak  ammonia  by 
decantation,  and  then  on  the  filter  until  the  filtrate  gives  no  precipitate  with 
sodic  phosphate.  Dilute  nitric  acid  is  next  poured  into  the  beaker  to  dissolve 
the  precipitate  adhering  to  the  glass,  thence  on  to  the  precipitate  on  the 


280  VOLUMETRIC   ANALYSIS.  §    69. 

filter.  The  nitric  solution  is  received  in  a  beaker  holding  about  150  c.c.  and 
marked  at  77  c.c.  After  two  or  three  washings  with  acidulated  water  the 
filter  itself  is  detached  from  the  funnel  and  added  to  the  contents  of  the 
beaker,  as  the  paper  is  found  to  retain  traces  of  P205  even  after  many 
washings.  Dilute  ammonia  is  next  added  until  a  slight  turbidity  is  produced, 
which  is  removed  by  the  addition  of  one  or  two  drops  nitric  acid,  the  liquid 
is  heated  to  boiling,  5  c.c.  of  the  sodic  acetate  solution  added  (page  274,  3c.) 
and  the  titration  with  uranic  nitrate  immediately  proceeded  with. 

The  Standard  Uranic  Nitrate  is  made  by  dissolving  about  40  gm.  of  the 
pure  crystals  in  800  c.c.  water,  adding  a  few  drops  of  ammonia  to  produce  a 
slight  turbidity,  then  acetic  acid  until  cleared,  and  diluting  to  1  liter.  Acetate 
of  uranium  should  not  be  used,  as  it  impairs  the  sensibility  of  the  end-reaction. 
The  uranium,  solution  is  titrated  with  10  c.c.  of  a  standard  solution  of  acid 
ammonic  phosphate  containing  8'10  gm.  of  the  pure  dry  salt  per  liter 
(1  c.c.=0'005  gm.  P2O5).  The  ammonic  phosphate  solution  is  verified  by 
evaporating  a  measured  quantity  (say  50  c.c.)  of  it  to  dryness  with  a  measured 
quantity  of  a  solution  of  pure  ferric  nitrate  containing  an  excess  of  ferric 
oxide,  and  calcining  the  residue.  The  difference  in  weight  between  this 
calcined  residue  and  that  from  an  equal  volume  of  ferric  nitrate  solution 
evaporated  alone,  is  the  weight  of  phosphoric  anhydride  contained  in  the 
50  c.c.  of  ammonic  phosphate  solution.  The  actual  verification  of  the 
uranic  nitrate  is  performed  by  measuring  accurately  10  c.c.  of  the  ammonic 
phosphate  into  a  beaker  marked  at  75  c.c.,  adding  5  c.c.  of  the  sodic 
acetate,  making  up  with  water  to  about  30  c.c.,  and  heating  to  boiling. 
9  c.c.  uranium  are  then  run  in  from  a  burette,  and  the  liquid  tested  in  the 
usual  way  with  ferrocyanide.  Prom  this  point  the  uranium  is  added  two  or 
three  drops  at  a  time,  until  the  end-reaction  just  appears,  the  burette  being 
read  off  at  each  testing.  As  soon  as  the  faintest  colouration  appears, 
the  beaker  is  immediately  filled  to  the  mark  with  boiling  distilled  water, 
and  another  test  made.  If  the  operation  has  been  properly  conducted  no 
brown  colour  will  be  detected,  owing  to  the  dilution  of  the  liquid,  and  one 
or  two  drops  more  of  the  uranium  solution  must  be  added  before  the  colour 
becomes  evident,  and  the  burette  is  finally  read  off.  A  constant  correction  is 
subtracted  from  all  readings  obtained  in  this  way :  it  is  the  quantity  of 
uranium  found  necessary  to  give  the  end-reaction  with  5  c.c.  of  the  sodic 
acetate  solution  alone,  diluted  to  75  c.c.  with  boiling  water  as  above  described. 
The  end-point  must  always  be  verified  by  adding  three  or  four  drops  of 
uranium  in  excess,  and  testing  again,  when  a  strongly  marked  colour  should 
be  produced.  The  standard  uranium  is  made  of  the  same  strength  as  the 
standard_  ammonic  phosphate,  in  order  to  eliminate  the  error  caused  by 
changes  in  the  temperature  of  the  laboratory.  The  actual  analysis  is  made  in 
the  same  way  as  the  titration  of  the  standard  uranium,  except  that  a  slight 
error  is  introduced  by  the  number  of  tests  that  have  to  be  made  abstracting 
a  small  fraction  of  the  assay.  To  correct  this,  a  second  estimation  should 
always  be  made,  and  nearly  the  whole  of  the  uranium  found  necessary  in  the 
first  trial  should  be  added  at  once.  Tests  are  then  made  at  intervals  of  two 
or  three  drops,  and  the  final  and  correct  result  should  slightly  exceed  that 
obtained  in  the  first  trial. 

8.      Stolba's    Alkalimetric    Method. 

This  process  has  given  me  very  good  results  in  the  analysis  of 
superphosphates  containing  iron  and  alumina,  even  if  the  quantity 
of  these  substances  is  very  considerable,  such  as  mostly  occurs 
when  the  total  P205  has  to  be  estimated  in  a  given  manure,  and 
where  the  hydrochloric  acid  solution  has  necessarily  contained  all 
the  iron  or  alumina  present  in  the  substance. 


§    69.  PHOSPHORIC    ACID.  281 

The  Analysis :  The  clear  aqueous  solution  of  1  gm.  of  a  superphosphate, 
or  the  acid  solution  of  the  soluble  and  insoluble  phosphates,  is  placed  into  a 
beaker  holding  about  150  c.c.,  and  from  30  to  50  c.c.  of  citro-inagnesia 
solution  added  according  to  the  proportion  of  P2O5.  A  good  excess  of  strong 
ammonia  is  added,  and  vigorously  stirred,  regardless  of  rubbing  the  sides  of 
the  beaker.  If  the  stirring  is  done  at  intervals  of  a  few  minutes,  it  is 
possible  to  separate  the  whole  of  the  P2O5  in  half  an  hour,  but  for  safety  the 
mixture  may  be  left  at  rest  for  another  half-hour ;  then  the  liquid  filtered 
through  a  porous  filter,  washing  the  main  precipitate  and  the  filter  with 
alcohol  or  methylated  spirit  of  50  per  cent,  until  all  free  ammonia  is 
removed.  The  stirring  rod  and  sides  of  the  beaker  will  be  covered  with 
crystals,  which  need  not  be  detached,  but  must  be  carefully  washed  with  the 
dilute  alcohol ;  and  finally,  the  main  precipitate  may  be  transferred  to  the 
filter  to  drain ;  but  before  this  is  done,  the  first  strong  ammoniacal  filtrate 
should  be  removed  from  beneath  the  funnel,  so  that  no  volatile  ammonia 
may  contaminate  the  precipitate  or  filter.  In  fact,  all  care  must  be  taken 
to  remove  ammonia,  except  that  which  is  chemically  combined  with  the 
magnesia  and  the  phosphoric  acid ;  this  being  done,  the  original  beaker  and 
stirring  rod  are  placed  under  the  funnel,  and  a  measured  excess  of  y^ 
sulphuric,  nitric,  or  hydrochloric  acid  is  poured  over  the  filter  and  precipitate 
in  repeated  small  quantities  until  the  double  phosphate  is  completely 
dissolved.  Finally,  the  whole  is  washed  with  repeated  portions  of  hot  water, 
so  that  all  the  salt  is  extracted  from  the  folds  of  the  filter,  and  a  perfect^ 
clear  solution  of  all  the  crystals  from  the  rod  and  sides  of  the  beaker  is 
obtained. 

The  titration  is  made  by  cooling  the  liquid  to  ordinary  temperature, 
and  adding  a  drop  or  two  of  methyl  orange  or  rosolic  acid,  then  titrating 
residually  with  •£$  ammonia  or  other  alkali. 

The  volume  of  -~j  acid  neutralized  by  the  alkaline  double 
phosphate,  when  multiplied  by  O00355,  will  give  the  weight  of 
P205,  or  by  0-00775,  the  weight  of  Ca3P208  in  the  1  gm.  of 
material  used. 

The  process  is  one  of  delicacy,  and  cannot  be  used  except  by 
experienced  manipulators. 


9.      Pemberton's    Molybdic    Method. 

This  process,  with  all  the  steps  that  led  to  its  adoption,  and  the 
difficulties  involved,  is  described  in  a  paper  read  before  the  chemical 
section  of  the  Franklin  Institute  in  1882  (C.  N.  xlvi.  4). 

The  process  is  based  on  the  fact  that,  if  a  standard  aqueous 
solution  of  ammonic  molybdate  be  added  to  one  of  phosphoric 
acid,  in  the  presence  of  a  large  proportion  of  ammonic  nitrate, 
accompanied  with  a  small  excess  of  nitric  acid,  and  heat  applied  to 
the  mixture,  the  whole  of  the  P205  is  immediately  and  completely 
carried  down  as  phospho-molybdate  quite  free  from  MoO3.  A  small 
excess  of  the  precipitant  renders  the  supernatant  liquid  clear  and 
colourless,  and  the  ratio  of  molybdic  trioxide  to  phosphoric 
anhydride  is  always  the  same. 

The  weak  part  of  the  method  is  the  difficulty  in  finding  the 
exact  point  at  which  the  precipitation  is  ended,  because  the 


282  VOLUMETRIC   ANALYSIS.  §    69. 

yellow  precipitate  does  not  settle  in  clots  like  silver  chloride, 
and  hence  nitration  is  necessary,  in  order  to  obtain  a  portion  of 
clear  liquid  for  testing  with  a  drop  of  the  niolybdate.  Very  good 
results  may  be  obtained  with  some  little  patience  and  practice  by 
using  the  Beale  filter  (fig.  19).  When  the  precipitation  is  thought 
to  be  nearly  complete,  the  filter  is  dipped  into  the  hot  liquid,  so 
as  to  obtain  2  c.c.  or  so  in  a  clear  condition  :  this  is  transferred 
to  a  clean  test  tube  or  small  short  beaker,  and  a  drop  or  two 
of  the  precipitant  added,  then  heated  in  the  bath  to  see  if  a  yellow 
colour  occurs ;  if  it  does,  the  filter  and  beaker  are  washed  again 
into  the  bulk  with  hot  water  in  very  small  quantities  from  a  small 
wash  bottle.  A  second  titration  ought  to  result  in  a  very  near 
approximation,  and  a  third  will  be  exact.  A  convenient  small 
suction  asbestos  filter  is  figured  and  described  by  Professor 
C  aid  well  as  well  adapted  to  this  process  (C.  N.  xlviii.  61). 
As  each  titration  can  be  made  in  a  very  short  time,  and  iron  or 
alumina  may  be  totally  disregarded  in  moderate  quantity,  the 
process  may  be  made  valuable  for  technical  purposes. 

It  is,  however,  imperative  here,  as  it  is  in  the  usual  molybdic 
process,  to  avoid  the  presence  of  soluble  silica,  organic  matter, 
and  organic  acids.  Chlorides  in  moderate  quantity  do  not 
interfere. 

The  necessary  solutions  and  reagents  are — 

•  Standard  Ammonic  niolybdate.  89*543  gm.  of  the  crystallized 
salt  are  dissolved  in  about  900  c.c.  of  water ;  if  not  quite  clear, 
a  very  few  drops  of  ammonia  may  be  added  to  ensure  perfect 
solution  ;  the  flask  is  then  filled  to  the  liter  mark.  The  weight  of 
salt  used  is  based  on  the  proportion  of  24  MoO3  to  1  of  P205,  and 
each  c.c.  precipitates  3  m.gm.  P205.  If  any  doubt  exists  as  to  the 
purity  of  the  niolybdate,  the  solution  should  be  standardized  with 
a  solution  of  P205  of  known  strength.  In  any  case  this  is  to  be 
recommended. 

Ammonic  nitrate  in  granular  form  and  neutral. 

Mtric  acid,  sp.  gr.  not  less  than  1*4  ;  or  if  of  less  strength,  a 
proportionate  increase  must  be  used  in  the  titration. 

The  Analysis:  The  phosphate  to  be  titrated  is  taken  in  quantity  con- 
taining not  over  O'l  gin.  P2O5  or  0'15  gm.  at  the  utmost.  If  silica  is  present, 
the  solution  is  evaporated  to  dryness.  In  presence  of  organic  matter  ignite 
gently  and  evaporate  to  dryness  twice  with  HNO3.  There  is  no  advantage 
in  filtering  off  the  SiO2.  The  solution  is  transferred  to  a  beaker  of  100  to 
125  c.c.,  using  as  little  water  as  possible  to  prevent  unnecessary  dilution 
and  is  just  neutralized  with  NH4HO,  i.e.,  until  a  slight  precipitate  is 
formed. 

If  much  iron  is  present  the  ammonia  is  added  until  the  yellow  colour  begins 
to  change  to  a  darlcer  shade.  2  c.c.  of  nitric  acid  are  added.  Care  must  be 
taken  that  the  sp.  gr.  of  the  acid  is  not  less  than  1'4,  otherwise  more  must 
be  added.  10  gm.  of  granular  nitrate  of  ammonia  are  now  added.  After 
a  little  experience  the  quantity  can  be  judged  with  sufficient  accuracy  by  the 


§  69.  pHOsrHOEic  ACID.  283 

eye  without  the  trouble  of  weighing.  The  solution  is  now  heated  to  140°  P. 
or  over  and  the  molybdate  solution  run  in  (most  conveniently  from  a  Gay 
Lussac  burette),  meanwhile  stirring  the  liquid.  The  beaker  is  now  left 
undisturbed  for  about  a  minute  on  the  water-bath  or  hot  plate  until  the 
precipitate  settles,  leaving  the  supernatant  liquid  not  clear  but  containing 
widely  disseminated  particles,  in  which  the  yellow  cloud  can  easily  be  seen 
on  the  further  addition  of  the  molybdate.  This  addition  is  continued  as  long 
as  the  precipitate  is  thick  and  of  a  deep  colour.  But  as  soon  as  it  becomes 
rather  faint  and  thin,  a  little  of  the  solution,  about  2  to  3  c.c.,  after  settling 
of  the  precipitate,  is  filtered  into  a  very  small  beaker,  and  this  is  heated  on 
a  hot  plate  and  4  or  5  drops  of  the  molybdate  added.  If  a  precipitate  is 
produced,  the  whole  is  poured  back  into  the  large  beaker,  and  a  further 
addition  of  the  molybdate  (1,  2,  or  3  c.c.)  added,  according  to  the  quantity 
of  the  precipitate  in  the  small  beaker.  After  stirring  and  settling,  another 
small  quantity  is  filtered  and  again  tested.  If  the  mark  has  been  overstepped 
and  too  much  molybdate  added,  a  measured  quantity  of  P2O5  solution  of 
known  strength  is  added,  and  the  corresponding  amount  of  P2O5  deducted. 
The  results  may  be  checked  by  adding  1  c.c.  of  standard  P2O5  solution,  and 
then  again  testing.  This  can  be  repeated  as  often  as  desired.  The  portion 
that  finally  produces  a  cloud  is  the  end-point ;  from  this  is  deducted  0'5  c.c. 
(for  neutralizing  the  solvent  action  of  the  nitric  acid),  the  remainder 
multiplied  by  3  gives  the  weight  of  P2O5  in  milligrams.  O'l  gm.  of  P2O5 
gives  about  2  '75  gm.  of  the  yellow  precipitate,  and  the  accuracy  of  the 
method  is  largely  due  to  the  low  percentage  of  P2O5. 


10.      Schindler's    Method. 

This  method  is  based  on  the  precipitation  of  the  phosphoric  acid 
as  phospho-molybdate  of  definite  composition  which  is  secured  by 
adding  citric  acid  to  the  ordinary  molybdate  solution  in  the  pro- 
portion of  15  gm.  to  1  liter.  50  c.c.  of  the  nitric  acid  solution  of 
the  phosphate  (0'5  gm.  of  substance)  is  mixed  with  so  much  of 
a  solution  of  ammonic  nitrate  (750  gm.  per  liter),  that  after  the 
addition  of  the  molybdate  the  mixture  shall  contain  25  gm.  of 
ammonic  nitrate  per  100  c.c.  Then  for  each  O'l  gm.  of  phosphoric 
anhydride,  100  c.c.  of  molybdate  solution  is  added,  and  the 
mixture  is  heated  in  a  water  bath  to  about  58°.  The  precipitate 
is  allowed  to  deposit  for  10  minutes,  the  supernatant  liquid  is 
filtered,  and  the  precipitate  is  washed  three  or  four  times  with 
dilute  ammonic  nitrate  (100  gm.  with  10  c.c.  of  nitric  acid  per 
liter).  It  is  then  dissolved  in  3  per  cent,  ammonia,  treated  with 
10  to  20  c.c.  of  magnesia  mixture,  and  made  up  to  250  c.c.  After 
shaking,  it  is  filtered :  50  c.c.  of  the  filtrate  is  acidified  with 
acetic  acid,  diluted  to  300  c.c.  with  hot  water,  and  titrated  with 
lead  acetate.  Comparative  determinations  on  a  variety  of  materials 
show  a  close  agreement  with  the  magnesia  method. 

Further  details  of  the  reactions  involved  are  contained  in  the 
section  on  Molybdenum,  and  it  is  necessary  to  study  these  in 
carrying  out  the  process. 


284  VOLUMETRIC  ANALYSIS.  §    70. 


SILVER. 

Ag=107-66. 

c.c.  or  1  dm.  ~  sotlic  chloride  =  0*010766  gin.  or  0'10766  grn. 
Silver;  also  0 '01 6 96 6  gm.  or  0*16966  grn.  Silver  nitrate. 


1.      Precipitation    with    JQ    Sodic    Chloride. 

§  70.  THE  determination  of  silver  is  precisely  the  converse  of 
the  operations  described  under  chlorine  (§37,  1  and  2),  and  the 
process  may  either  be  concluded  by  adding  the  sodic  chloride  till 
no  further  precipitate  is  produced,  or  potassic  chromate  may  be 
used  as  an  indicator.  In  the  latter  case,  however,  it  is  advisable 
to  add  the  salt  solution  in  excess,  then  a  drop  or  two  of  chromate, 
and  titrate  residually  with  y^  silver,  till  the  red  colour  is  produced, 
for  the  excess  of  sodic  chloride. 


2.      By    Ammonic    Sulphocyanate    (Thiocyanate). 

The  principle  of  this  method  is  fully  described  in  §  39,  and 
need  not  further  be  alluded  to  here.  The  author  of  the  method 
(Volhard)  states,  that  comparative  tests  made  by  this  method 
and  that  of  GayLussac  gave  equally  exact  results,  both  being- 
controlled  by  cupellation,  but  claims  for  this  process  that  the  end 
of  the  reaction  is  more  easily  distinguished,  and  that  there  is  no 
labour  of  shaking,  or  danger  of  decomposition  by  light,  as  in  the 
case  of  chloride. 


3.     Estimation   of   Silver,    in    Ores   and    Alloys,    by   Starch    Iodide 
(Method    of   Pisani    and    F.    Field). 

If  a  solution  of  blue  starch-iodide  be  added  to  a  neutral  solution 
of  silver  nitrate,  while  any  of  the  latter  is  in  excess  the  blue  colour 
disappears,  the  iodine  entering  into  combination  with  the  silver  •  as 
soon  as  all  the  silver  is  thus  saturated,  the  blue  colour  remains 
permanent,  and  marks  the  end  of  the  process.  The  reaction  is 
very  delicate,  and  the  process  is  more  especially  applicable  to  the 
analysis  of  ores  and  alloys  of  silver  containing  lead  and  copper,  but 
not  mercury,  tin,  iron,  manganese,  antimony,  arsenic,  or  gold  in 
solution. 

The  solution  of  starch  iodide,  devised  by  Pisani,  is  made  by 
rubbing  together  in  a  mortar  2  gm.  of  iodine  with  15  gm.  of  starch 
and  about  6  or  8  drops  of  water,  putting  the  moist  mixture  into  a 
stoppered  flask,  and  digesting  in  a  water  bath  for  about  an  hour,  or 
until  it  has  assumed  a  dark  bluish-grey  colour ;  water  is  then  added 
till  all  is  dissolved.  The  strength  of  the  solution  is  then  ascertained 


§  70.  SILVER.  285 

by  titrating  it  with  10  c.c.  of  a  solution  of  silver  containing  1  gin. 
in  the  liter,  to  which  a  portion  of  pure  precipitated  calcic  carbonate 
is  added ;  the  addition  of  this  latter  removes  all  excess  of  acid,  and 
at  the  same  time  enables  the  operator  to  distinguish  the  end  of  the 
reaction  more  accurately.  The  starch  iodide  solution  should  be  of 
such  a  strength  that  about  50  c.c.  are  required  for  10  c.c.  of  the 
silver  solution  (  =  O'Ol  gm.  silver). 

F.  Field  (C.  N.  ii.  17),  who  discovered  the  principle  of  this 
method  simultaneously  with  Pisani,  uses  a  solution  of  iodine  in 
potassic  iodide  with  starch.  Those  who  desire  to  make  use  of 
this  plan  can  use  the  —^  and  yj^  solutions  of  iodine  described 
in  §34. 

In  the  analysis  of  silver  containing  copper,  the  solution  must  be 
considerably  diluted  in  order  to  weaken  the  colour  of  the  copper ; 
a  small  measured  portion  is  then  taken,  calcic  carbonate  added,  and 
starch  iodide  till  the  colour  is  permanent.  It  is  best  to  operate 
with  about  from  60  to  100  c.c.,  containing  not  more  than  0'02  gm. 
silver ;  when  the  quantity  is  much  greater  than  this,  it  is  preferable 
to  precipitate  the  greater  portion  with  —  sodic  chloride,  and  to 
complete  with  starch  iodide  after  filtering  off  the  chloride.  When 
lead  is  present  with  silver  in  the  nitric  acid  solution,  add  sulphuric 
acid,  and  filter  off  the  lead  sulphate,  then  add  calcic  carbonate  to 
neutralize  excess  of  acid,  filter  again  if  necessary,  then  add  fresh 
carbonate  and  titrate  as  above. 


4.     Assay  of  Commercial  Silver   (Plate,   Bullion,   Coin,   etc.).     Gay 
Lussac's   Method   modified   by   J.    Q-.    Mulder. 

For  more  than  thirty  years  Gay  Lussac's  method  of  estimating 
silver  in  its  alloys  has  been  practised  intact,  at  all  the  European 
mints,  under  the  name  of  the  "  humid  method,"  in  place  of  the  old 
system  of  cupellation.  During  that  time  it  has  been  regarded  as  one 
of  the  most  exact  methods  of  quantitative  analysis.  The  researches 
of  Mulder,  however,  into  the  innermost  details  of  the  process 
have  shown  that  it  is  capable  of  even  greater  accuracy  than  has 
hitherto  been  gained  by  it. 

The  principle  of  the  process  is  the  same  as  described  in  §  37, 
depending  on  the  affinity  which  chlorine  has  for  silver  in  preference 
to  all  other  substances,  and  resulting  in  the  formation  of  chloride 
of  silver,  a  compound  insoluble  in  dilute  acids,  and  which  readily 
separates  itself  from  the  liquid  in  which  it  is  suspended. 

The  plan  originally  devised  by  the  illustrious  inventor  of  the 
process  for  assaying  silver,  and  which  is  still  followed,  is  to  consider 
the  weight  of  alloy  taken  for  examination  to  consist  of  1000  parts, 
and  the  question  is  to  find  how  many  of  these  parts  are  pure  silver. 
This  empirical  system  was  arranged  for  the  convenience  of  commerce, 
and  being  now  thoroughly  established,  it  is  the  best  plan  of 
procedure.  If,  therefore,  a  standard  solution  of  salt  be  made  of 


286  VOLUMETRIC   ANALYSIS.  §    70. 

such  strength  that  100  c.c.  will  exactly  precipitate  1  gm.  of  silver, 
it  is  manifest  that  each  ^  c.c.  will  precipitate  1  m.gm.  or  10100 
part  of  the  gram  taken;  and  consequently  in  the  analysis  of 
1  gm.  of  any  alloy  containing  silver,  the  number  of  ^  c.c. 
required  to  precipitate  all  the  silver  out  of  it  would  be  the  number 
of  thousandths  of  pure  silver  contained  in  the  specimen. 

In  practice,  however,  it  would  not  do  to  follow  this  plan  precisely, 
inasmuch  as  neither  the  measurement  of  the  standard  solution  nor 
the  ending  of  the  process  would  be  gained  in  the  most  exact 
manner;  consequently,  a  decimal  solution  of  salt,  one-tenth  the 
strength  of  the  standard  solution,  is  prepared,  so  that  1000  c.c. 
will  exactly  precipitate  1  gm.  of  silver,  and,  therefore,  1  c.c. 
1  m.gm. 

The  silver  alloy  to  be  examined  (the  composition  of  which  must 
be  approximately  known)  is  weighed  so  that  about  1  gm.  of  pure 
silver  is  present ;  it  is  then  dissolved  in  pure  nitric  acid  by  the  aid 
of  a  gentle  heat,  and  100  c.c.  of  standard  solution  of  salt  added 
from  a  pipette  in  order  to  precipitate  exactly  1  gm.  of  silver ;  the 
bottle  containing  the  mixture  is  then  well  shaken  until  the  chloride 
of  silver  has  curdled,  leaving  the  liquid  clear. 

The  question  is  now  :  Which  is  in  excess,  salt  or  silver  ?  A  drop 
of  decimal  salt  solution  is  added,  and  if  a  precipitate  be  produced 
1  c.c.  is  delivered  in,  and  after  clearing,  another,  and  so  on  as  long 
as  a  precipitate  is  produced.  If  on  the  other  hand  the  one  drop  of 
salt  produced  no  precipitate,  showing  that  the  pure  silver  present 
was  less  than  1  gm.,  a  decimal  solution  of  silver  is  used,  prepared 
by  dissolving  1  gm.  pure  silver  in  pure  nitric  acid  and  diluting  to 
1  liter.  This  solution  is  added  after  the  same  manner  as  the  salt 
solution  just  described,  until  no  further  precipitate  occurs ;  in  either 
case  the  quantity  of  decimal  solution  used  is  noted,  and  the  results 
calculated  in  thousandths  for  1  gm.  of  the  alloy. 

The  process  thus  shortly  described  is  that  originally  devised  by 
Gay  Lussac,  and  it  was  taken  for  granted  that  when  equivalent 
chemical  proportions  of  silver  and  sodic  chloride  were  brought  thus 
in  contact,  that  every  trace  of  the  metal  was  precipitated  from  the 
solution,  leaving  sodic  nitrate  and  free  nitric  acid  only  in  solution. 
The  researches  of  Mulder,  however,  go  to  prove  that  this  is  not 
strictly  the  case,  but  that  when  the  most  exact  chemical  proportions 
of  silver  and  salt  are  made  to  react  on  each  other,  and  the  chloride 
has  subsided,  a  few  drops  more  of  either  salt  or  silver  solution  will 
produce  a  further  precipitate,  indicating  the  presence  of  both  silver 
nitrate  and  sodic  chloride  in  a  state  of  equilibrium,  which  is  upset 
on  the  addition  of  either  salt  or  silver.  Mulder  decides,  and  no 
doubt  rightly,  that  this  peculiarity  is  owing  to  the  presence  of  sodic 
nitrate,  and  varies  somewhat  with  the  temperature  and  state  of 
dilution  of  the  liquid. 

It  therefore  follows  that  when  a  silver  solution  is  carefully 
precipitated,  first  by  concentrated  and  then  by  dilute  salt  solution, 


§  70.  SILVER.  287 

until  no  further  precipitate  appears,  the  clear  liquid  will  at  this 
point  give  a  precipitate  with  dilute  silver  solution ;  and  if  it  he 
added  till  no  further  cloudiness  is  produced,  it  will  again  he 
precipitable  "by  dilute  salt  solution. 

Example :  Suppose  that  in  a  given  silver  analysis  the  decimal  salt  solution 
lias  been  added  so  long  as  a  precipitate  is  produced,  and  that  1  c.c.  (=20  drops 
of  Mulder's  dropping  apparatus)  of  decimal  silver  is  in  turn  required  to 
precipitate  the  apparent  excess,  it  would  be  found  that  when  this  had  been 
done,  1  c.c.  more  of  salt  solution  would  be  wanted  to  reach  the  point  at  which 
no  further  cloudiness  is  produced  by  it,  and  so  the  changes  might  be  rung 
time  after  time;  if,  however,  instead  of  the  last  1  c.c.  (=20  drops)  of  salt, 
half  the  quantity  be  added,  that  is  to  say  10  drops  (  =  £  c.c.),  Mulder's 
so-called  neutral  point  is  reached ;  namely,  that  in  which,  if  the  liquid  be 
divided  in  half,  both  salt  and  silver  will  produce  the  same  amount  of 
precipitate.  At  this  stage  the  solution  contains  silver  chloride  dissolved 
in  sodic  nitrate,  and  the  addition  of  either  salt  or  silver  expels  it  from 
solution. 

A  silver  analysis  may  therefore  he  concluded  in  three  ways — 

( 1 )  By  adding  decimal  salt  solution  until  it  just  ceases  to  produce 
a  cloudiness. 

(2)  By  adding  a  slight  excess  of  salt,  and  then  decimal  silver 
till  no  more  precipitate  occurs. 

(3)  By  finding  the  neutral  point. 

According  to  Mulder  the  latter  is  the  only  correct  method,  and 
preserves  its  accuracy  at  all  temperatures  up  to  56°  C.  (  =  133° 
Fahr.),  while  the  difference  hetween  1  and  3  amounts  to  J  a  m.gm., 
and  that  hetween  1  and  2  to  1  m.gm.  on  1  gm.  of  silver  at 
16°  C.  (  =  60°  Fahr.),  and  is  seriously  increased  hy  variation  of 
temperature. 

It  will  readily  he  seen  that  much  more  trouhle  and  care  is 
required  hy  Mulder's  method  than  hy  that  of  GayLussac,  hut, 
as  a  compensation,  much  greater  accuracy  is  obtained. 

On  the  whole,  it  appears  to  me  preferable  to  weigh  the  alloy  so 
that  slightly  more  than  1  gm.  of  silver  is  present,  and  to  choose  the 
ending  No.  1,  adding  drop  hy  drop  the  decimal  salt  solution  until 
just  a  trace  of  the  precipitate  is  seen,  and  which,  after  some  practice, 
is  known  hy  the  operator  to  he  final.  It  will  he  found  that  the 
quantity  of  salt  solution  used  will  slightly  exceed  that  required  hy 
chemical  computation;  say  100*1  c.c.  are  found  equal  to  1  gm.  of 
silver,  the  operator  has  only  to  calculate  that  quantity  of  the  salt 
solution  in  question  for  every  1  gm.  of  silver  he  assays  in  the  form 
of  alloy,  and  the  error  produced  hy  the  solubility  of  silver  chloride 
in  sodic  nitrate  is  removed. 

If  the  decimal  solution  has  been  cautiously  added,  and  the 
temperature  not  higher  than  17°  C.  (62°  Fahr.),  this  method  of 
conclusion  is  as  reliable  as  No.  3,  and  free  from  the  possible  errors 
of  experiment;  for  it  requires  a  great  expenditure  of  time  and 
patience  to  reverse  an  assay  two  or  three  times,  each  time 
cautiously  adding  the  solutions,  drop  by  drop,  then  shaking  and 


288  VOLUMETRIC  ANALYSIS.  §    70. 

waiting  for  the  liquid  to  clear,  besides  the  risk  of  discolouring  the 
chloride  of  silver,  which  would  at  once  vitiate  the  results. 

The  decimal  silver  solution,  according  to  this  arrangement,  would 
seldom  be  required ;  if  the  salt  has  been  incautiously  added,  or  the 
quantity  of  alloy  too  little  to  contain  1  gm.  pure  silver,  then  it  is 
best  to  add  once  for  all  2,  3,  or  5  c.c.,  according  to  circumstances, 
and  finish  with  decimal  salt  as  No.  1,  deducting  the  silver  added. 

The   Standard   Sohitions   and  Apparatus. 

(a)  Standard  Salt  Solution. — Pure  sodic  chloride  is  prepared  by  treating 
a  concentrated  solution  of  the  whitest  table-salt  first  with  a  solution  of 
caustic  baryta  to  remove  sulphuric  acid  and  magnesia,  then  with  a  slight 
excess  of  sodic  carbonate  to  remove  baryta  and  lime,  warming  and  allowing 
the  precipitates  to  subside,  then  evaporating  to  a  small  bulk  that  crystals 
may  form;  these  are  separated  by  a  filter,  and  slightly  washed  with  cold 
distilled  water,  dried,  removed  from  the  filter,  and  heated  to  dull  redness, 
and  when  cold  preserved  in  a  well-closed  bottle  for  use.  The  mother-liquor 
is  thrown  away,  or  used  for  other  purposes.  Of  the  salt  so  prepared,  or  of 
chemically  pure  rock-salt  (Steinsalz,  a  substance  to  be  obtained  freely  in 
Germany),  5*4145  gm.  are  to  be  weighed  and  dissolved  in  1  liter  of  distilled 
water  at  16°  C.  100  c.c.  of  this  solution  will  precipitate  exactly  1  gm.  of 
silver.  It  is  preserved  in  a  well-stoppered  bottle,  and  shaken  before  use. 

(5)  Decimal  Salt  Solution. — 100  c.c.  of  the  above  solution  are  diluted  to 
exactly  1  liter  with  distilled  water  at  16°  C.  1  c.c.  will  precipitate  O'OOl  gm. 
of  silver. 

(c)  Decimal  Silver  Solution. — Pure  metallic  silver  is  best  prepared  by 
galvanic  action  from  pure  chloride ;  and  as  clean  and  secure  a  method  as  any 
is  to  wrap  a  lump  of  clean  zinc,  into  which  a  silver  wire  is  melted,  with 
a  piece  of  wretted  bladder  or  calico,  so  as  to  keep  any  particles  of  impurity 
contained  in  the  zinc  from  the  silver.  The  chloride  is  placed  at  the  bottom 
of  a  porcelain  dish,  covered  with  dilute  sulphuric  acid,  and  the  zinc  laid  in 
the  middle ;  the  silver  wire  is  bent  over  so  as  to  be  immersed  in  the  chloride. 
As  soon  as  the  acid  begins  to  act  upon  the  zinc  the  reduction  commences  in 
the  chloride,  and  grows  gradually  all  over  the  mass ;  the  resulting  finely- 
divided  silver  is  well  washed,  first  with  dilute  acid,  then  with  hot  water,  till 
all  acid  and  soluble  zinc  are  removed. 

The  moist  metal  is  then  mixed  with  a  little  sodic  carbonate,  saltpetre, 
and  borax,  say  aoout  an  eighth  part  of  each,  dried  perfectly,  then  melted. 
Mulder  recommends  that  the  melting  should  be  done  in  a  porcelain  crucible 
immersed  in  sand  contained  in  a  common  earthen  crucible ;  borax  is  sprinkled 
over  the  surface  of  the  sand  so  that  it  may  be  somewhat  vitrified,  that  in 
pouring  out  the  silver  when  melted  no  particles  of  dirt  or  sand  may  fall  into 
it.  If  the  quantity  of  metal  be  small  it  may  be  melted  in  a  porcelain  crucible 
over  a  gas  blowpipe. 

The  molten  metal  obtained  in  either  case  can  be  poured  into  cold  water 
and  so  granulated,  or  upon  a  slab  of  pipe-clay,  into  which  a  glass  plate  has 
been  pressed  when  soft  so  as  to  form  a  shallow  mould.  The  metal  is  then 
washed  well  with  boiling  water  to  remove  accidental  surface  impurities,  and 
rolled  into  thin  strips  by  a  goldsmith's  mill,  in  order  that  it  may  be  readily 
cut  for  weighing.  The  granulated  metal  is,  of  course,  ready  for  use  at  once 
without  any  rolling. 

1  gm.  of  this  silver  is  dissolved  in  pure  dilute  nitric  acid,  and 
diluted  to  1  liter ;  each  c.c.  contains  0*001  gm.  of  silver.  It  should 
be  kept  from  the  light. 


§  70.  SILVER.  289 

(d)  Dropping-  Apparatus  for  Concluding-  the  Assay. — Mulder 
constructs  a  special  affair  for  this  purpose,  consisting  of   a  pear- 
shaped   vessel   fixed   in  a  stand,   with   special   arrangements   for 
preventing  any  continued  flow  of  liquid.     The  delivery  tube  has  an 
opening  of  such  size  that  20  drops  measure  exactly  1  c.c.     The 
vessel  itself  is   not  graduated.     As  this  arrangement  is  of   more 
service  to  assay  than  to  general  laboratories,  it  need  not  be  further 
described  here.     A  small  burette  divided  in  —^  c.c.  with  a  conve- 
nient dropping  tube,  will  answer  every  purpose,  and  possesses  the 
further  advantage  of  recording  the  actual  volume  of  fluid  delivered. 

The  100-c.c.  pipette,  for  delivering  the  concentrated  salt  solution, 
must  be  accurately  graduated,  and  should  deliver  exactly  100  gm. 
of  distilled  water  at  16°  C. 

The  test  bottles,  holding  about  200  c.c.,  should  have  their 
stoppers  well  ground  and  brought  to  a  point,  and  should  be  fitted 
into  japanned  tin  tubes,  reaching  as  high  as  the  neck,  so  as  to  pre- 
serve the  precipitated  chloride  from  the  action  of  light,  and,  when 
shaken,  a  piece  of  black  cloth  should  be  covered  over  the  stopper. 

(e)  Titration  of  the  Standard  Salt  Solution. — From  what  has 
been  said  previously  as  to  the  principle  of  this  method,  it  will  be 
seen  that  it  is  not  possible  to  rely  absolutely  upon  a  standard  solu- 
tion of    salt   containing   5 '4 145  gm.   per  liter,   although   this   is 
chemically  correct  in  its  strength.     The  real  working  power  must 
be  found  by  experiment.     From  1*002  to  1*004  gm.  of  absolutely 
pure  silver  is  weighed  on  the  assay  balance,  put  into  a  test  bottle 
with  about  5  c.c.  of  pure  nitric  acid,  of  about  1*2  sp.  gr.,  and  gently 
heated  in  the  water  or  sand  bath  till  it  is  all  dissolved.      The 
nitrous  vapours  are  then  blown  from  the  bottle,  and  it  is  set  aside 
to  cool  down  to  about  16°  C.  or  60°  Fahr. 

The  100  c.c.  pipette,  which  should  be  securely  fixed  in  a  support, 
is  then  carefully  filled  with  the  salt  solution,  and  delivered  into 
the  test  bottle  contained  in  its  case,  the  moistened  stopper  inserted, 
covered  over  with  the  black  velvet  or  cloth,  and  shaken  con- 
tinuously till  the  chloride  has  clotted,  and  the  liquid  becomes  clear ; 
the  stopper  is  then  slightly  lifted,  and  its  point  touched  against  the 
neck  of  the  bottle  to  remove  excess  of  liquid,  again  inserted,  and 
any  particles  of  chloride  washed  down  from  the  top  of  the  bottle 
by  carefully  shaking  the  clear  liquid  over  them.  The  bottle  is 
then  brought  under  the  decimal  salt  burette,  and  J  c.c.  added,  the 
mixture  shaken,  cleared,  another  J  c.c.  put  in,  and  the  bottle  lifted 
partly  out  of  its  case  to  see  if  the  precipitate  is  considerable ; 
lastly,  2  or  3  drops  only  of  the  solution  are  added  at  a  time  until 
no  further  opacity  is  produced  by  the  final  drop.  Suppose,  for 
instance,  that  in  titrating  the  salt  solution  it  is  found  that  1*003  gm. 
of  silver  require  100  c.c.  concentrated,  and  4  c.c.  decimal  solution, 
altogether  equal  to  100*4  c.c.  concentrated,  then — 

1*003  silver  :  100*4  salt  :  :  1*000  :  x,  #=  100*0999. 

u 


290  VOLUMETRIC   ANALYSIS.  §    70. 

The  result  is  within  y^J^^  of  100*1,  which  is  near  enough  for  the 
purpose,  and  may  be  more  conveniently  used.  The  operator 
therefore  knows  that  100*1  c.c.  of  the  concentrated  salt  solution 
at  16°  C.  will  exactly,  precipitate  1  gm.  silver,  and  calculates 
accordingly  in  his  examination  of  alloys. 

In  the  assay  of  coin  and  plate  of  the  English  standard,  namely, 
11*1  silver  and  0'9  copper,  the  weight  corresponding  to  1  gm.  of 
silver  is  1-081  gm.,  therefore  in  examining  this  alloy  1-085  gm. 
may  be  weighed. 

When  the  quantity  of  silver  is  not  approximately  known,  a 
preliminary  analysis  is  necessary,  which  is  best  made  by  dissolving 
J  or  1  gm.  of  the  alloy  in  nitric  acid,  and  precipitating  very 
carefully  with  the  concentrated  salt  solution  from  a  ~$  c.c.  burette. 
Suppose  that  in  this  manner  1  gm.  of  alloy  required  45  c.c.  salt 
solution, 

100-1  salt  :  1-000  silver  :  :  45  :  x.  x  =  0-4495. 
Again  0-4495  :  1   :  :  1-003  :  x=2'231. 

2 '2 31  gm.   of  this  particular  alloy  are  therefore  taken  for  the 


Where  alloys  of  silver  contain  sulphur  or  gold,  with  small 
quantities  of  tin,  lead,  or  antimony,  they  are  first  treated  with  a 
small  quantity  of  nitric  acid  so  long  as  red  vapours  are  disengaged, 
then  boiled  with  concentrated  sulphuric  acid  till  the  gold  has 
become  compact,  set  aside  to  cool,  diluted  with  water,  and  titrated 
as  above. 

Assaying    on    the    Grain    System. 

It  will  be  readily  seen  that  the  process  just  described  may  quite 
as  conveniently  be  arranged  on  the  grain  system  by  substituting  10 
grains  of  silver  as  the  unit  in  place  of  the  gram  ;  each  decem  of 
concentrated  salt  solution  would  then  be  equal  to  —  of  a  grain 
of  silver,  and  each  decem  of  decimal  solution  to  T^-g-  of  a  grain. 


5.      Analysis    of   the    Silver    Solutions    used    in    Photography. 

The  silver  bath  solutions  .for  sensitizing  collodion  and  paper 
frequently  require  examination,  as  their  strength  is  constantly 
lessening.  To  save  calculation,  it  is  better  to  use  an  empirical 
solution  of  salt  than  the  systematic  one  described  above. 

This  is  best  prepared  by  dissolving  43  grains  of  pure  sodic 
chloride  in  1  0,000  grains  of  distilled  water.  Each  decem  (  =  10  grn.  ) 
of  this  solution  will  precipitate  0'125  grn.  (i.e.  -J-  grn.)  of  pure 
silver  nitrate  ;  therefore,  if  one  fluid  drachm  of  any  silver  solution 
be  taken  for  examination,  the  number  of  decems  of  salt  solution 
required  to  precipitate  all  the  silver  will  be  the  number  of  grains 
of  silver  nitrate  in  each  ounce  of  the  solution. 


§  71.  SUGAR.  291 

Example :  One  fluid  drachin  of  an  old  nitrate  bath  was  carefully  measured 
into  a  stoppered  bottle,  10  or  15  drops  of  pure  nitric  acid  and  a  little  distilled 
water  added ;  the  salt  solution  was  then  cautiously  added,  shaking  well  after 
each  addition  until  no  further  precipitate  was  produced.  The  quantity 
required  was  26' 5  dm.=26i  grains  of  silver  nitrate  in  each  ounce  of 
solution. 

Crystals  of  silver  nitrate  may  also  be  examined  in  the  same  way, 
by  dissolving  say  30  or  40  grn.  in  an  ounce  of  water,  taking  one 
drachm  of  the  fluid  and  titrating  as  above. 

In  consequence  of  the  rapidity  and  accuracy  with  which  silver 
may  be  determined,  when  potassic  chromate  is  used  as  indicator, 
some  may  prefer  to  use  that  method.  It  is  then  necessary  to  have 
a  standard  solution  of  silver,  of  the  same  chemical  power  as  the 
salt  solution :  this  is  made  by  dissolving  125  grains  of  pure  and 
dry  neutral  silver  nitrate  in  1000  dm.  of  distilled  water ;  both 
solutions  will  then  be  equal,  volume  for  volume. 

Suppose,  therefore,  it  is  necessary  to  examine  a  silver  solution 
used  for  sensitizing  paper.  One  drachm  is  measured,  and 
if  any  free  acid  be  present,  cautiously  neutralized  with  a  weak 
solution  of  sodic  carbonate ;  100  dm.  of  salt  solution  are  then 
added  with  a  pipette.  If  the  solution  is  under  100  grn.  to 
the  ounce,  the  quantity  will  be  sufficient.  3  or  4  drops  of 
chromate  solution  are  then  added,  and  the  silver  solution  delivered 
from  the  burette  until  the  red  colour  of  silver  chromate  is  just 
visible.  If  25 -5  dm.  have  been  required,  that  number  is  deducted 
from  the  100  dm.  of  salt  solution,  which  leaves  74*5  dm.,  or 
74J  grains  to  the  ounce. 

This  method  is  much  more  likely  to  give  exact  results  in  the 
hands  of  persons  not  expert  in  analysis  than  the  ordinary  plan  by 
precipitation,  inasmuch  as,  with  collodion  baths,  containing  as  they 
always  do  silver  iodide,  it  is  almost  impossible  to  get  the  supernatant 
liquid  clear  enough  to  distinguish  the  exact  end  of  the  analysis. 


§  71.  THE  term  sugar  is  applied  to  several  bodies  possessing 
distinct  properties,  and  differing  somewhat  in  molecular  com- 
position, also  differing  materially  in  their  effects  upon  various 
reagents. 

The  methods  in  general  use  for  the  estimation  of  the  various 
kinds  of  sugar  are,  the  optical  method,  by  the  polariscope  or 
polarizing  saccharometer ;  by  gravimetric  analysis  with  copper 
solution,  and  volumetric  analysis  by  copper  or  mercury  solutions. 
The  two  last  depend  upon  the  reducing  power  possessed  by  various 
kinds  of  saccharine  substances  upon  the  oxides  of  copper  or 
mercury. 

The  study  of  the  nature  of  the  various  sugars,  and  their  effects 

u  2 


292  VOLUMETRIC   ANALYSIS.  §    71. 

upon  certain  reagents,  is  one  of  great  interest  and  importance,  and 
lias  given  rise  to  very  extensive  researches,  including  the  transfor- 
mation products  of  starch,  malt,  etc.* 

The  discussion  of  the  intricate  organic  changes  which  occur  in 
vegetable  juices,  or  the  starches,  in  relation  to  the  sugar  they 
contain,  or  are  capable  of  developing,  is  far  too  complicated  a  matter 
to  be  entered  upon  here ;  but  those  who  may  be  concerned  in  the 
study  of  such  subjects  will  derive  great  advantage  from  the  perusal 
of  the  admirable  papers  of  0' Sullivan  and  of  Brown  and  Heron, 
which  may  be  regarded  as  models  of  research  in  this  particular 
branch  of  organic  chemistry.  The  varieties  of  sugar  of  general 
importance  are — 

(1)  Those  that  possess  the  chemical  composition  of  grape  sugar 
or  glucose,  C6H1206,  such  as  the  sugar  contained  in  the  juice  of 
grapes,   apples,  and  other  ripe  fruit;    also  that  which  occurs  in 
urine  in  Diabetes  mellitus. 

(2)  Common  cane  sugar,  C12H22011,  contained  in  the  juice  of 
the  sugar  cane,  beet  root,  maple,  malt  sugar,  etc. 

Sugars  of  the  latter  class,  and  also  those  contained  in  milk,  may 
all  be  altered  in  character  (inverted)  by  boiling  for  a  short  period 
with  weak  sulphuric  or  hydrochloric  acid. 

These  inverted  sugars  are  not  identically  the  same  as  grape  sugar, 
and  they  each  have  their  peculiar  effect  upon  the  copper  or  mercury 
solutions  used  for  estimating  them.  Cane  sugar  in  a  pure  state  has 
no  reducing  action  upon  the  metallic  solutions. 

The  volumetric  method  of  estimating  glucose  by  Fehling's 
copper  solution  has  for  a  long  time  been  thought  open  to  question 
on  the  score  of  accuracy,  and  the  extensive  and  elaborate  experi- 
ments of  Soxhlet  have  clearly  shown,  that  only  under  identical 
conditions  of  dilution,  etc.,  can  concordant  results  be  obtained. 
The  high  official  position  of  this  chemist,  together  with  the  evident 
care  shown  in  his  methods,  leave  no  doubt  as  to  the  general 
accuracy  of  his  conclusions.  His  rather  sweeping  statement,  how- 
ever, that  the  accurate  gravimetric  estimation  of  glucose  by 
Fe Ming's  solution  is  impossible,  is  strongly  controverted  by 
Brown  and  Heron,  whose  large  experience  leads  them  to  a 
different  conclusion.  It  is  probable,  however,  that  both  authorities 
are  right  from  their  OAvn  points  of  view,  and  that  Brown  and 
Heron  do  obtain  concordant  results  when  working  in  precisely  the 
same  way;  whereas  Soxhlet  is  equally  correct  in  stating  that 
the  gravimetric  estimation,  as  usually  performed  under  varying 
•conditions,  is  open  to  serious  errors. 

"Kumpf  and  Heintzerling,  Z.  o.  C.  ix.  358. 
O'Sullivan,  J.  C.  S.  1872,  579,  etc.,  etc. 
Marker,  Landw.  Versuchs-Stat.  xxii.  69. 
Musculus  and  Gruber,  Bull.  Soc.  Chim.  xxx.  54. 
Httfner,  Jour.f.  pract.  Chem.  [2]  v.  372. 
Brown  and  Heron,  J.  C.  S.  1879.  596. 
Soxhlet,  Jour.f.  pract.  Chem.  [2]  xxi.  227. 
Allen's  Organic  Analysis  i.  187—348,  2nd  edit. 


§  71.  SUGAK.  293 

The  Solution  of  Stigrar. — For  -all  the  processes  of  titration  this 
must  be  so  diluted  as  to  contain  J  or  at  most  1  per  cent  of  sugar : 
if  on  trial  it  is  found  to  be  stronger  than  this,  it  must  be  further 
diluted  with  a  measured  quantity  of  distilled  water. 

If  the  sugar  solution  to.be  examined  is  of  dark  colour,  or  likely 
to  contain  extractive  matters  which  might  interfere  with  the 
distinct  ending  of  the  reaction,  it  is  advisable  to  heat  a  measured 
quantity  to  boiling,  and  add  a  few  drops  of  milk  of  lime,  allow  the 
precipitate  to  settle,  then  filter  through  purified  animal  charcoal, 
iind  dilute  with  the  washings  to  a  definite  volume.  In  some 
instances  cream  of  alumina  or  basic  lead  acetate  may  be  used  to 
clarify  highly  coloured  or  impure  solution,  but  no  lead  must  be 
left  in  the  solution.* 

From  thick  mucilaginous  liquids,  or  those  which  contain  a  large 
proportion  of  albuminous  or  extractive  matters,  the  sugar  is  best 
extracted  by  Graham's  dialyser. 

The  Feh ling  method  may  be  applied  directly  to  fresh  diabetic 
urine  (see  Analysis  of  Urine),  as  also  to  brewer's  wort  or  distiller's 
mash.  Dextrine  does  not  interfere,  except  the  boiling  of  the 
liquid  under  titration  is  long  continued. 


INVERSION    OF    VARIOUS    SUGARS    INTO    GLUCOSE. 

The  various  kinds  of  sucrose  such  as  cane,  milk,  malt,  and  other 
less  familiar  forms  of  sugar  must  be  inverted  before  they  can  be 
estimated  as  glucose  by  the  Fehling  process ;  the  scientific  term 
for  this  change  is  "  hydrolysis,"  or  re-arrangement  of  the  elements 
of  water  in  the  saccharine  substance.  This  inversion  may  be 
caused  by  heating  with  acids  or  by  treatment  with  yeast  or 
diastase,  but  acids  are  the  agents  by  which  the  process  is  carried 
out  for  volumetric  or  gravimetric  estimation  with  copper  or 
mercury.  Ordinary  cane  sugar  is  best  inverted  by  heating  to 
about  70°  C.  a  dilute  solution  (in  no  case  should  the  concentration 
exceed  25  per  cent.)  of  the  sugar  with  10  per  cent,  of  fuming 
hydrochloric  acid  for  15  minutes.  Dilute  sulphuric  acid  is 
preferred  by  some  operators.  If  the  mixture  is  boiled,  the 
inversion  occurs  in  from  5  to  10  minutes.  The  inversion  of  milk 
sugar  takes  longer  time  than  cane  sugar. 

Maltose  or  malt  sugar  takes  a  much  longer  time  than  milk 
sugar,  but  may  be  done  by  the  addition  of  3  c.c.  of  concentrated 
sulphuric  acid  to  100  c.c.  of  wort,  and  heating  for  3  hours  in 

*  Although  traces  of  lead  are  of  no  great  consequence  when  clarifying  sugars  for  the 
polariscope,  it  is  of  great  importance  to  remove  all  lead  in  the  volumetric  method.  In 
order  to  do  this  it  is  best  to  treat  a  measured  quantity  of  the  sugar  solution  which  has 
been  clarified  hy  lead  with  a  strong  solution  of  sulphurous  acid  until  no  further 
precipitate  occurs,  then  add  a  few  drops  of  alumina  hydrate  suspended  in  water, 
dilute  to  a  definite  volume  and  filter.  In  many  cases  concentrated  solution  of  sodic 
carbonate  will  suffice  to  remove  all  lead.  These  methods  of  clarification  are  highly 
necessary  in  the  case  of  albuminous  or  gelatinous  liquids,  as  otherwise  the  copper  oxide 
will  not  settle  readily,  and  it  becomes  difficult  to  tell  when  the  end-reaction  occurs. 


294  VOLUMETRIC  ANALYSIS.  §    71. 

a  boiling  water  bath ;  if  dextrine  is  present,  it  is  also  inverted  at 
the  same  time. 

The  inversion  of  the  slowly  changing  sugars  may  be  hastened 
considerably  by  heating  at  increased  atmospheric  pressure,  although 
some  authorities  condemn  the  process.  O'Sullivan  however 
states  that  a  good  result  with  maltose  or  dextrine  is  obtained  by 
heating  30  gnu  of  the  substance  in  100  c.c.  of  water  containing 
1  c.c.  of  H2S04  for  20  minutes,  at  a  pressure  of  one  additional 
atmosphere  (Allen's  Organic  Analysis  i.  217). 

Allen  also  gives  a  handy  means  of  carrying  out  this  method, 
which  consists  in  using  a  soda  water  bottle  with  rubber  stopper 
through  which  passes  a  long  glass  tube  bent  at  right  angles,  and 
immersed  to  a  depth  of  30  inches  in  mercury  contained  in 
a  vertical  tube  of  glass  or  metal.  The  rubber  stopper  must  be 
secured  by  wire,  and  the  bottle  heated  to  boiling  in  a  saturated 
solution  of  sodic  nitrate,  which  gives  a  temperature  corresponding 
to  an  extra  atmosphere.  Of  course  in  all  cases  where  acid  has 
been  used  for  the  inversion  of  sugar,  it  must  be  neutralized  before 
the  copper  titration  takes  place ;  this  may  be  done  either  with 
sodic  or  potassic  hydrates  or  carbonates,  or  calcic  carbonate  may  be 
used. 

Starch  from  various  sources  may  be  inverted  in  the  same  way 
as  the  sugars,  but  it  needs  a  prolonged  heating  with  acid.  For 
approximate  purposes  1  gin.  of  starch  should  be  mixed  to  a  smooth 
cream  with  about  30  c.c.  of  cold  water,  then  1  c.c.  of  strong 
hydrochloric  acid  added,  and  the  mixture  kept  at  a  boiling 
temperature  in  an  obliquely  fixed  flask  for  8  or  10  hours,  replacing 
the  evaporated  water  from  time  to  time  to  avoid  charring  the 
sugar,  and  testing  with  iodine  to  ascertain  when  the  inversion 
is  complete.  The  product  is  glucose. 

100  parts  of  grape  sugar,  found  by  Fehling's  process,  represent 
90  parts  of  starch  or  dextrine.  When  dextrine  is  present  with 
grape  sugar,  care  must  be  taken  not  to  boil  the  mixture  too  long 
with  the  alkaline  copper  solution,  as  it  has  been  found  that  a  small 
portion  of  the  copper  is  precipitated  by  the  dextrine  (Rumpf  and 
Heintzerling,  Z.  a.  C.  ix.  358). 

An  inversion  of  starch  may  be  produced  more  rapidly,  and  at 
lower  temperature,  by  using  some  form  of  diastase  in  place  of 
acid.  An  infusion  of  malt  is  best  suited  to  the  purpose,  but  the 
temperature  must  not  exceed  71°  C.  (160°  Fahr.).  The  digestion 
may  vary  from  fifteen  minutes  to  as  many  hours.  The  presence  of 
unchanged  starch  may  be  found  by  occasionally  testing  with  iodine. 
If  the  digestion  is  carried  beyond  half  an  hour,  a  like  quantity  of 
the  same  malt  solution  must  be  digested  alone,  at  the  same 
temperature,  and  for  the  same  time,  then  titrated  for  its  amount  of 
sugar,  which  is  deducted  from  the  total  quantity  found  in  the 
mixture.  O'Sullivan  (/.  C.  S.  1872,  579)  has,  however,  clearly 
shown  that  the  effect  of  the  so-called  diastase  is  to  produce  maltose, 


§  71.  SUGAR.  295 

which  has  only  the  power  of  reducing  the  copper  solution  to  the 
extent  of  about  three-fifths  that  of  dextrose  or  true  grape  sugar, 
the  rest  being  probably  various  grades  of  dextrine.  Brown  and 
Heron's  experiments  clearly  demonstrate  that  no  dextrose  is 
produced  from  starch  by  even  prolonged  treatment  with  malt 
extract ;  the  only  product  is  maltose.  Sulphuric  or  other  similar 
acids  cause  complete  inversion. 

For  the  exact  estimation  of  starch  in  grain  of  various  kinds 
O'Sullivan  gives  very  elaborate  directions,  involving  the  treat- 
ment of  the  substance  with  alcohol  and  ether,  to  remove  fatty  and 
other  constituents  previous  to  digestion  with  diastase.  The  same 
authority  also  gives  special  directions  for  the  preparation  of  the 
proper  kind  of  diastase,  all  of  which  may  be  found  in  J".  C.  S. 
xlv.  1. 

Preparation  of   the   Standard  Solutions. 

Feh ling's  Standard  Copper  Solution. — Crystals  of  pure  cupric 
sulphate  are  powdered  and  pressed  between  unsized  paper  to 
remove  adhering  moisture ;  69 '28  gm.  are  weighed,  dissolved  in 
water,  about  1  c.c.  of  pure  sulphuric  acid  added,  and  the  solution 
diluted  to  1  liter. 

Alkaline  Tartrate  Solution. — 350  gm.  of  Eochelle  salt  (sodio- 
potassic  tartrate)  are  dissolved  in  about  700  c.c.  of  water,  and  the 
solution  filtered,  if  not  already  clear ;  there  is  then  added  to  it  a 
clear  solution  of  100  gm.  of  caustic  soda  (prepared  by  alcohol)  in 
about  200  c.c.  of  water.  The  volume  is  made  up  to  1  liter. 

These  solutions  are  preserved  separately,  and,  when  mixed  in 
exactly  equal  proportions,  form  the  original  Fehling  solution,  which 
should  contain  in  each  c.c.  0'03464  gm.  of  cupric  sulphate,  and  has 
hitherto  been  taken  to  represent  0'005  gm.  of  pure  anhydrous 
grape  sugar,  the  supposition  being  that  10  equivalents  of  copper 
are  reduced  from  the  state  of  cupric  to  cuprous  oxide  by  1  equiva- 
lent of  grape  sugar.*  Soxhlet,  however,  has  with  great  pains 
prepared  specimens  of  pure  sugars  of  various  types  which  have 
been  used  as  standards  for  the  verification  of  these  hitherto- 
received  conclusions  of  Fehling,  Neubauer,  and  others,  and 
which  show  that  the  ratio  of  reduction  is  dependent  upon  various 
conditions  of  dilution,  duration  of  experiment,  etc.,  hitherto  not 
taken  into  account;  the  results  will  be  given  further  on.  The 

*  If  pure  cupric  sulphate  lias  been  used,  and  the  solutions  mixed  only  at  the  time  of 
titration,  there  need  be  very  little  fear  of  inaccuracy ;  nevertheless  ic  is  advisable  to 
verify  the  mixed  solutions  from  time  to  time.  This  may  be  done  by  weighing  and 
dissolving  0'95  gm.  of  pure  cane  sugar  in  about  500  c.c.  of  water,  adding  2  c.c.  of 
hydrochloric  acid,  and  heating  to  70°  C.  for  ten  minutes.  The  acid  is  then  neutralized 
with  sodic  carbonate  and  diluted  to  a  liter.  50  c.c.  of  this  liquid  should  exactly 
reduce  the  copper  in  10  c.c.  of  Fehling's  solution.  A  standard  solution  of  inverted 
sugar,  which  will  keep  good  for  many  months,  may  be  made  in  the  foregoing  manner : 
it  should  be  of  about  20  per  cent,  strength,  and  rendered  strongly  alkaline  with  soda  or 
potash. 


296  VOLUMETUIC  ANALYSIS.  §    71. 

principle  of  Fehling's  method  is  based  on  the  fact  that  although 
the  copper  solution,  as  described  above,  may  be  heated  to  boiling 
without  change,  the  introduction  into  it  of  the  smallest  quantity  of 
grape  sugar,  at  a  boiling  temperature,  at  once  produces  a  precipitate 
of  cuprous  oxide,  the  amount  of  reduction  being  in  the  ratio 
above  mentioned. 

Knapp's  Standard  Mercuric  cyanide. — 10  gm.  of  pure  dry 
mercuric  cyanide  are  dissolved  in  about  600  c.c.  of  water;  100  c.c. 
of  caustic  soda  solution  (sp.  gr.  1*145)  are  added,  and  the  liquid 
diluted  to  1  liter. 

Sachsse's  Standard  Mercuric  iodide. — 18  gm.  of  pure  dry 
mercuric  iodide  and  25  gm.  of  potassic  iodide  are  dissolved  in 
water,  and  to  the  liquid  is  added  a  solution  of  80  gm.  of  caustic 
potash ;  the  mixture  is  finally  diluted  to  1  liter. 

These  solutions,  if  wrell  preserved,  will  hold  their  strength 
unaltered  for  a  long  period. 

These  solutions  are  very  nearly,  but  not  quite,  the  same  in 
mercurial  strength,  Knapp's  containing  7'9365  gm.  Hg  in  the 
liter,  Sachsse's  7 '92  95  gm.  100  c.c.  of  the  former  are  equal  to 
100-1  c.c.  of  the  latter. 

Indicators  for  the  Mercurial  Solutions. — In  the  case  of  Fehling's 
solution,  the  absence  of  blue  colour  acts  as  a  sufficient  indicator, 
but  with  mercury  solutions  the  end  of  reaction  must  be  found  by 
an  external  indicator.  In  the  case  of  Knapp's  solution  the  end  of 
the  reaction  is  found  by  placing  a  drop  of  the  clear  yellowish 
liquid  above  the  precipitate  on  pure  white  Swedish  filter  paper, 
then  holding  it  first  over  a  bottle  of  fuming  HC1,  then  over  strong 
sulphuretted  hydrogen  water ;  the  slightest  trace  of  free  mercury 
shows  a  light  brown  or  yellowish-brown  stain.  The  indicator  best 
adapted  for  Sachsse's  solution  is  a  strongly  alkaline  solution  of 
stannous  chloride  spotted  on  a  porcelain  tile.  An  excess  of 
mercury  gives  a  brown  colour. 

The  Titration  of  Glucose  with  Mercury  Solutions :  40  c.c.  of  either  are 
placed  in  a  porcelain  basin  or  a  flask,  diluted  with  an  equal  bulk  of  water, 
and  heated  to  boiling.  The  solution  of  sugar  of  £  per  cent,  strength  is  then 
delivered  in  until  all  the  mercury  is  precipitated,  the  theory  being  in  either 
case  that  40  c.c.  should  be  reduced  by  O'l  gm.  of  dextrose. 

The  results  of  Sox h let's  experiments  show  that  this  estimate 
is  entirely  wrong*;  nevertheless,  it  does  not  follow  that  these 
mercurial  solutions  are  useless.  It  is  found  that,  using  them  by 
comparison  with  Fehling's  solution,  it  is  possible  to  define  to 
some  extent  the  nature  of  mixed  sugars,  on  the  principle  of  indirect 
analysis. 

*  Careful  experiment  shows  that  40  c.c.  of  Sachsse's  solution  is  reduced  by  01342 
gm.  dextrose  or  0'1072  gm.  invert  sugar. 


§  71.  SUGAR.  297 

Knapp's  solution  is  strongly  recommended  by  good  authorities 
for  the  estimation  of  diabetic  sugar  in  urine.  The  method  of  using 
it  is  described  in  the  section  on  Urinary  analysis. 

The  Titration  of  Glucose  with  Fehling's  Solution— 5  c.c.  each  of 
standard  copper  and  alkaline  tartrate  solutions  are  accurately  measured  into 
a  thin  white  porcelain  basin,  40  c.c.  of  water  added,  and  the  basin  quickly 
heated  to  boiling  on  a  sand-bath  or  by  a  small  flame.  No  reduction  or 
change  of  colour  should  occur ;  if  it  does,  the  alkaline  tartrate  solution 
is  probably  defective  from  age.  This  may  probably  be  remedied  by  the 
addition  of  a  little  fresh  caustic  alkali  on  second  trial,  but  it  is  advisable  to 
use  a  new  solution.  The  i  or  1  per  cent,  sugar  solution  is  then  delivered  in 
from  a  burette  *  in  small  quantities  at  a  time,  with  subsequent  boiling,  until 
the  blue  colour  of  the  copper  solution  is  just  discharged,  a  point  which  is 
readily  detected  by  inclining  the  basin,  so  that  the  colour  of  the  clear 
supernatant  fluid  may  be  observed  against  the  white  sides  of  the  basin. 
Some  operators  use  a  small  thin  boiling  flask  instead  of  the  basin. 

It  is  almost  impossible  to  hit  the  exact  point  of  reduction  in  the 
first  titration,  but  it  affords  a  very  good  guide  for  a  more  rapid  and 
exact  addition  of  the  sugar  solution  in  a  second  trial,  when  the 
sugar  may  be  added  with  more  boldness,  and  the  time  of  exposure 
of  the  copper  solution  to  the  air  lessened,  which  is  a  matter  of 
great  importance,  since  prolonged  boiling  has  undoubtedly  a 
prejudicial  effect  on  the  accuracy  of  the  process.! 

When  the  exact  point  of  reduction  is  obtained,  it  is  assumed 
that  the  volume  of  sugar  solution  used  represents  0'05  gin.  of  grape 
sugar  or  dextrose,  or  that  1  equivalent  of  dextrose  (  =  180)  exactly 
reduces  10  equivalents  of  cupric  oxide  (  =  397). 

With  this  assumption,  however,  Sox  hie  t  does  not  agree,  but 
maintains  from  the  results  of  his  experiments  on  carefully  prepared 
standard  sugars,  that  the  accuracy  of  the  reaction  is  interfered 
with  by  varying  concentration  of  the  solutions,  duration  of  the 
experiment,  and  the  character  of  the  sugar. 

The  critical  experiments  of  Sox h let]:  were  both  volumetric 
and  gravimetric,  and  may  be  summarized  as  follows  : — 

The  reducing  power  of  a  sugar  was  volumetrically  determined  in 
the  following  manner : — Varying  quantities  of  the  copper  solution 
were  heated  to  boiling  in  a  dish,  equal  volumes  of  the  alkaline 
tartrate  solution  being  previously  added.  Then  50  c.c.  or  100  c.c. 
of  the  1  per  cent,  or  J  per  cent,  sugar  solutions  respectively  were 
added,  and  the  whole  was  boiled  for  two,  four,  or  six  minutes, 
according  to  the  variety  of  the  sugar.  The  contents  of  the  dish 

*  The  instrument  should  he  ai'ranged  as  described  on  page  11. 

t  It  has  heen  proposed  to  use  an  excess  of  copper,  and  to  estimate  the  excess 
iodometrically  or  with  cyanide  (§  54)  in  view  of  the  alleged  uncertain  ending  in  the 
ordinary  P  eh  ling  process.  My  experiments  with  these  methods  show  that  the  errors 
are  greater  than  the  one  they  are  supposed  to  cure.  Moreover,  in  practised  hands  the 
true  ending  presents  no  difficulty. 

J  A  very  admirable  and  complete  resume  of  Soxhlet's  results  is  given  in  a  paper 
read  before  the  School  of  Pharmacy  Students'  Association  by  C.  H.  Hutchinson,  F.C.S. 
(Pharm.  Journ.  Feb.  1881,  720). 


298  YOLUMETKIC  ANALYSIS.  §    71. 

are  then  thrown  on  a  filter,  the  filtrate  is  acidified  with  acetic  acid, 
and  potassic  ferrocyanide  at  once  added  to  ascertain  the  presence  of 
copper.  This  process  is  repeated  until  two  quantities  of  the  copper 
solution,  differing  from  each  other  by  y1^  c.c.,  give,  the  one  a  filtrate 
containing  copper,  the  other  a  filtrate  free  from  copper.  The  mean 
of  these  two  readings  is  taken  as  the  result. 

The  gravimetric  method  of  determining  the  copper  reduced  by 
the  sugars  acting  on  Fehling's  or  Lowe's  solution  (hydrated 
cupric  oxide  dissolved  in  an  alkaline  solution  of  glycerine)  is  to 
boil  a  measured  quantity  of  the  sugar  solution  with  an  excess  of 
the  Fehling's  or  Lowe's  solution,  and  then  to  filter  by  means  of 
gentle  suction,  through  a  weighed  tube  filled  with  asbestos ;  wash 
with  hot  Avater,  then  with  absolute  alcohol,  and  finally  with  ether. 
On  passing  hydrogen  through  the  heated  tube,  the  cuprous  oxide  is 
reduced  to  the  metallic  state  in  two  or  three  minutes,  and  then 
weighed.  The  following  are  the  chief  results  : — 

Dextrose. — 0'5  gm.  in  1  per  cent,  solution  reduces  105-2  c.c.  of 
Fehling  (undiluted),  or  101*1  c.c.  of  Fehling  (diluted  with  4 
volumes  of  water). 

Eatio  of  reduction,  1   :  10'52 — 1   :  10-11. 

Invert  Sugar  (i.e.  equal  molecules  of  dextrose  and  levulose 
obtained  by  the  action  of  acids  on  cane-sugar). — 0'5  gm.  in  1  per 
cent,  solution  reduces  101 -2  c.c.  of  Fehling  (undiluted),  or  97*0 
c.c.  of  Fehling  (diluted  with  4  volumes  of  water). 

Eatio  of  reduction,  1   :  10-12— 1   :  97. 

In  the  case  of  dextrose  and  invert  sugar,  dilution  of  the  solution 
lowers,  excess  of  copper  raises,  the  reducing  power. 

Milk  Sugar. — 0'5  gm.  in  1  per  cent,  solution  reduces  74  c.c. 
of  Fehling. 

Eatio  of  reduction,  1   :  7  "4. 

Dilution  has  no  noteworthy  influence  on  the  reducing  power. 
Excess  of  copper  raises  it,  but  to  a  much  slighter  extent  than  with 
dextrose  or  invert  sugar. 

Galactose. — 0"5  gm.  in  1  per  cent,  solution  reduces  98  c.c. 
of  Fehling  (undiluted),  or  94  c.c.  of  Fehling  (diluted  with 
4  volumes  of  water). 

Eatio  of  reduction,  1   :  9-8—1   :  9 -4. 

Dilution  lessens  the  reducing  power  to  the  same  extent  as  with 
dextrose  and  invert  sugar.  Excess  of  copper  raises  the  reducing 
power,  but  to  somewhat  slighter  extent  than  with  dextrose  and 
invert  sugar. 

Levulose  (calculated  from  the  results  with  dextrose  and  invert 
sugar). — 0-5  gm.  in  1  per  cent,  solution  reduces  97*2  c.c.  of 
Fehling  (undiluted),  or  93  c.c.  of  Fehling  (diluted  with  4  volumes 
of  water). 


§  71.  SUGAE.  299 

Katio  of  reduction,  1   :  9 '7  2 — 1   :  9 -3. 

Dilution  and  excess  of  copper  act  respectively  as  with  dextrose 
and  invert  sugar.  The  reducing  power  of  levulose  is  probably 
equal  to  that  of  galactose. 

Inverted  Milk  Sugar  (made  by  heating  ordinary  milk  sugar  with 
acids). — Keducing  power  equal  to  that  of  invert  sugar. 

Maltose. — 0'5  gm.  in  1  per  cent,  solution  reduces  64*2  c.c.  of 
Fehling  (undiluted),  or  6 7 '5  c.c.  of  Fehling  (diluted  with  4 
volumes  of  water). 

Katio  of  reduction,  1   :  6-09—1   :  6'41. 

Dilution  raises  the  reducing  power.  Excess  of  copper  has  no 
effect  with  undiluted  Fehling,  but  in  highly  dilute  solutions 
raises  the  reducing  power  to  a  slight  extent. 

With  the  exception  of  the  determination  of  sugar  in  diabetic 
urine  (where,  owing  to  the  constant  formation  of  ammonia,  some  of 
the  cuprous  oxide  is  dissolved  and  passes  through  the  filter,  and 
consequently  the  end  of  the  reaction  must  be  decided,  as  usual,  by 
the  disappearance  of  the  blue  colour),  the  following  plan  is  adopted 
for  the  estimation  of  the  various  sugars.  The  approximate  strength 
of  the  sugar  solution  is  first  determined  in  the  usual  manner,  by 
the  disappearance  of  the  blue,  operating  on  25  c.c.  Fehling.  The 
sugar  solution  is  now  diluted  so  as  to  contain  1  per  cent,  of  the 
sugar,  and  the  determination  is  proceeded  with  as  described  above, 
operating  on  50  c.c.  Fehling,  undiluted  with  water. 

In  the  case  of  highly  coloured  fluids,  the  indication  with  potassic 
ferrocyanide  is  difficult  to  recognize,  the  reaction  with  sulphuretted 
hydrogen  giving  still  worse  results.  In  such  cases  the  following 
device  is  adopted : — The  filtrate  is  boiled  with  a  few  drops  of  the 
sugar  solution  in  a  beaker,  allowed  to  settle,  and  then  poured  off ; 
on  wiping  the  bottom  and  sides  of  the  beaker  with  a  piece  of  white 
filter-paper,  it  will  be  coloured  red  if  any  copper  still  remain  in  the 
solution. 

The  remarks  which  Soxhlet  appends  to  these  experiments  are 
thus  classified : — 

(1)  The  reducing  power  of  inverted  sugar,  for  alkaline  copper  solution,  is 
importantly  influenced  by  the  concentration  of   the  solutions :    a  smaller 
quantity  of  sugar  being  required  to  decompose  Fehling's  solution  in  the 
undiluted  state  than  when  it  is  diluted  with  1,  2,  3,  or  4  volumes  of  water. 
It  is  immaterial  whether  the  sugar  solution  be  added  to  the  cold  or  boiling 
copper  reagent. 

(2)  If  inverted  sugar  acts  on  a  larger  quantity  of  copper  solution  than  it 
is  just  able  to  reduce,  its  reducing  powrer  will  be  increased,  the  increment 
varying  according  to  the  amount  of  copper  in  excess  and  the  concentration 
of  the  cupric  liquid;   in  the  previous  experiments  the  equivalents  varied 
from  1  :  9'7  to  1  :  12*6,  these  numbers  being  by  no  means  the  limit  of 
possible  variation. 

(3)  In  a  volumetric  estimation  of  inverted  sugar  by  means  ofFehling's 
solution,  the  amount  of  copper  reduced  by  each  successive  addition  of  sugar 
solution  is  a  decreasing  quantity ;  the  results  obtained  are  therefore  perfectly 
empirical,  and  are  only  true  of  that  particular  set  of  conditions. 


300  VOLUMETRIC  ANALYSIS.  §    71. 

(4)  The  statement  that  1  equivalent  of  inverted  sugar  reduces  10 
equivalents  of  cupric  oxide  is  not  true,  the  hypothesis  that  0'5  gm.  inverted 
sugar  reduces  100  c.c.  of  Fehling's  solution  being  shown  to  be  incorrect; 
the  real  amount  under  the  conditions  laid  down  byFehling(l  volume  of 
alkaline  copper  solution,  4  volumes  of  water,  sugar  solution  £ — 1  per  cent.) 
being  97  c.c.,  the  results  obtained  under  this  hypothesis  are,  therefore,  3  per 
cent,  too  low.  Where,  however,  the  above  conditions  have  been  fulfilled,  the 
results,  although  not  absolutely,  are  relatively  correct ;  not  so,  however,  those 
obtained  by  gravimetric  processes,  since  the  interference  of  concentration  and 
excess  has  not  been  previously  recognized. 

The  behaviour  of  the  sugars  with  alkaline  mercury  solutions  was  tested 
both  with  Knapp's  solution  (alkaline  mercuric  cyanide)  and  Sachsse's 
solution  (alkaline  mercuric  iodide  in  potassic  iodide). 

It  was  found  that  different  results  are  obtained  from  Knapp's  solutions, 
according  as  the  sugar  solution  is  added  gradually,  or  all  at  once;  when 
gradually  added  more  sugar  being  required ;  with  Sachsse's,  however,  the 
reverse  is  the  case. 

To  get  comparable  results  the  sugar  must  be  added  all  at  once,  the  solution 
boiled  for  two  or  three  minutes,  and  the  liquid  tested  for  mercury,  always 
using  the  same  indicator;  in  using  the  alkaline  tin  solution  as  indicator, 
0*200— 0'202  gm.  of  grape  sugar  was  always  required  for  100  c.c.  Knapp, 
in  a  large  number  of  experiments.  It  is  remarkable  that  these  two  solutions, 
although  containing  almost  exactly  the  same  amount  of  mercury,  require 
very  different  quantities  of  sugar  to  reduce  equal  volumes  of  them.  This  is 
shown  to  be  due,  to  a  great  extent,  to  the  different  amounts  of  alkali  present 
in  them. 

The  amounts  of  mercury  solutions  which  1  gm.  of  sugar  in 
1  per  cent,  solution  reduces  are : — 

Grape  sugar 497*5  c.c.  (Knapp),  302*5  c.c.  (Sachsse). 

Invert  sugar 502*5  „  376*0 

Levulose  508*5  „  449*5             „ 

Milk  sugar    322*5  „  214*5 

Galactose 413*0  „  226*0 

Inverted  milk  sugar  448'0  „  258*0 

Maltose     317*5  „  197*6 

The  various  sugars  have  different  reducing  powers  for  the  alkaline 
mercury  solutions,  and  there  is  no  definite  relation  between  the 
amount  of  Knapp's  and  S a chsse's  solutions  required  by  them; 
the  amount  of  Sachsse's  solution,  to  which  100  c.c.  Knapp's 
correspond,  varying  from  54*7  c.c.  in  the  case  of  galactose,  to 
74*8  c.c.  in  the  case  of  invert  sugar. 

Taking  the  reducing  power  of  grape  sugar  =100,  the  reducing 
powers  of  the  other  sugars  are  : — 

Fehling  (undiluted).        Knapp.  Sachsse. 

Grape  sugar    100  100  100 

Invert  sugar    96*2  99*0  124*5 

Levulose  (calculated) 92*4  102*2  148*6 

Milk  sugar 70*3  64*9  70*9 

Galactose    93*2  83*0  74*8 

Inverted  milk  sugar  96*2  90*0  85*5 

Maltose  61*0  63*8  65*0 


§  ,71.  SUGAE.  301 

The  two  mercury  methods  have  no  advantage  in  point  of  accuracy 
or  convenience  over  Fell  ling's  method,  the  latter  having  the 
preference  on  account  of  the  great  certainty  of  the  point  at  which 
the  reduction  is  finished. 

The  mercury  methods  are,  however,  of  great  importance,  both 
for  the  identification  of  a  sugar  and  for  the  estimation  of  two 
sugars  in  presence  of  each  other,  as  proposed  by  Sachsse. 
For  instance,  in  the  estimation  of  grape  and  invert  sugars  in 
presence  of  each  other,  there  are  the  two  equations :  ax  +  by  =  'F, 
ex  +  dy  =  S. 

Where— 

a  =  number  of  1  c.c.  Fehling,  reduced  by  1  gm.  grape  sugar. 

6=                                      „  „         invert  sugar. 

c=                               Sachsse  „               „          grape  sugar. 

„  „                „         invert  sugar. 

Fehling,  used  for  1   vol.  sugar  solution. 

Sachsse  „               „              „ 

x  =  amount  of   grape  sugar  in  gms.  in  1  vol.  of   the  solution. 
y=           „          invert  sugar 

It  need  hardly  be  mentioned  that  the  above,  like  all  other  indirect 
methods,  leaves  room  for  increased  accuracy ;  but  nevertheless  the 
combination  of  a  mercury  method  with  a  copper  method  in  the 
determination  of  a  sugar  whose  nature  is  not  exactly  known,  gives 
a  more  serviceable  result  than  the  hitherto  adopted  plan,  by  which 
a  solution  that  reduced  10  c.c.  Fehling  was  said  to  contain  0'05  gm. 
of  sugar  (J.  G.  S.  Abstracts,  1880,  758). 


Sidersky's    Method. 

This  process  has  found  great  favour  among  French  sugar  experts, 
and  is  based  on  the  use  of  Soldaini's  cupric  solution,  which  was 
devised  to  remedy  the  faults  common  to  Fehling  and  other 
copper  solutions  containing  tartrated  and  caustic  or  carbonated 
alkalies. 

This  liquid  is  prepared,  according  to  Degener,  in  the  following 
manner : — 40  gm.  of  cupric  sulphate  is  dissolved  in  water,  and,  in 
another  vessel,  40  gm.  of  sodic  carbonate  is  also  dissolved  in  water. 
The  two  solutions  are  mixed,  and  the  copper  precipitated  in  the 
state  of  hydrobasic  carbonate.  The  precipitate  is  washed  with 
cold  water  and  dried.  This  precipitate  is  added  to  a  very  con- 
centrated and  boiling  solution  of  bicarbonate  of  potash  (about 
415  gm.)  and  agitated  until  the  whole  is  completely  or  nearly 
dissolved,  water  is  added  to  form  a  volume  of  1400  c.c.,  and  the 
whole  mass  heated  for  two  hours  upon  a  water-bath.  The  insoluble 
matter  is  filtered,  and  the  filtrate,  after  cooling,  is  of  a  deep  blue 
colour.  The  sensibility  of  this  liquid  is  so  great  that  it  gives  a 


302  VOLUMETRIC  ANALYSIS.  §    71. 

decided  reaction  with  0*0014  gm.  of  invert  sugar.     The  presence 
of  sucrose  in  the  solution  increases  this  sensibility  still  more. 

Sidersky  has  recently  offered  a  new  volumetric  method,  based 
upon  the  use  of  Soldaini's  solution.  With  sugars  the  same 
method  as  is  now  in  use  with  Fehliiig's  solution  can  easily  be 
followed,  watching  the  disappearance  of  the  blue  colour,  and 
testing  the  end  with  ferrocyanide  and  acetic  acid.  This  process 
offers  no  serious  objections  common  to  Fehling's  solution,  but  is 
inapplicable  to  coloured  sugar  solutions,  such  as  molasses,  etc.  For 
the  last  the  following  is  recommended : — 25  gm.  of  molasses  are 
dissolved  in  100  c.c.  of  water  and  sub-acetate  of  lead  added  in 
sufficient  quantities  to  precipitate  the  impurities,  and  the  volume 
raised  to  200  c.c.  and  filtered.  To  100  c.c.  of  the  filtrate  are 
added  25  c.c.  of  concentrated  solution  of  carbonate  of  soda, 
agitated,  and  filtered  again.  100  c.c.  of  the  second  filtrate  with 
excess  of  lead  removed  is  taken  for  analysis.  On  the  other  hand, 
100  c.c.  of  Soldaini's  solution  is  placed  in  a  flask  and  heated  five 
minutes  over  an  open  flame.  The  sugar  solution  is  now  added 
little  by  little,  and  the  heating  continued  for  five  minutes.  Finally, 
the  heat  is  withdrawn  and  cooled  by  turning  in  100  c.c.  of  cold 
water,  and  filtered  through  a  Swedish  filter,  washed  with  hot 
water,  letting  each  washing  run  off  before  another  addition.  Three 
or  four  washings  will  generally  remove  completely  the  alkaline 
reaction.  The  precipitate  is  then  washed  through  a  hole  in  the 
filter  into  a  flask,  removing  the  last  trace  of  copper.  25  c.c.  of 
normal  sulphuric  acid  is  added  with  two  or  three  crystals  of 
chlorate  of  potash,  and  the  Avhole  gently  heated  to  dissolve  com- 
pletely the  oxide  of  copper,  which  is  transformed  into  copper 
sulphate.  The  excess  of  sulphuric  acid  is  determined  by  a 
standard  ammonia  solution  (semi-normal),  of  which  the  best 
indicator  is  the  sulphate  of  copper  itself.  When  the  deep  blue 
colour  gives  place  to  a  greenish  tinge  the  titration  is  completed. 
The  method  of  titration  is  performed  as  follows : — Having  cooled 
the  contents  of  the  flask,  a  quantity  of  ammonia  equivalent  to 
25  c.c.  of  normal  sulphuric  acid  is  added.  From  a  burette 
graduated  into  one-tenth  c.c.  standard  sulphuric  acid  is  dropped 
in  drop  by  drop,  agitating  after  each  addition.  The  blue  colour 
disappears  with  each  addition  to  reappear  after  shaking.  When 
the  last  trace  of  ammonia  is  saturated  the  titration  is  complete, 
which  is  known  by  a  very  feeble  greenish  tinge.  The  number  of 
c.c.  is  read  from  the  burette,  which  is  equivalent  to  the  copper 
precipitated.  The  equivalent  of  copper  being  taken  at  317,  the 
normal  acid  equivalent  is  OO317  of  copper.  Multiplying  the 
copper  found  by  3546  the  invert  sugar  is  found.  A  blank  titration 
is  needed  to  accurately  determine  the  slight  excess  which  gives 
the  pale  green  tinge.* 

*  Report  of  Proceedings  of  Fifth  Annual  Convention  of  the  American  Association, 
of  Official  Agricultural  Chemists  (1888). 


§    71.  SUGAR.  303 

Pavy's   modified   Fehlingr   Process. 

This  method  consists  in  adding  ammonia  to  the  ordinary 
Fehling  solution,  by  which  means  the  precipitation  of  cuprous 
oxide  is  entirely  prevented,  the  end  of  the  reaction  being  shown  by 
the  disappearance  of  the  blue  colour  in  a  perfectly  clear  solution 
(G.  N.  xxxix.  77). 

The  solution  finally  recommended  by  Pavy  as  equivalent  in 
action  to  the  usual  F  eh  ling  test  is  made  as  follows : — Cupric 
sulphate  34*65  gm.,  Eochelle  salt  170  gm.,  caustic  potash  170  gm., 
dissolved  to  1  liter  with  distilled  water.  120  c.c.  are  then  mixed 
with  400  c.c.  of  ammonia  (sp.  gr.  0*88)  and  diluted  to  a  liter.  This 
liquid  constitutes  the  Pavy-Fehling  solution,  of  which  10  c.c.  = 
1  c.c.  Fehling,  the  glucose  reduction  ratio  being  1  to  6  instead  of 
1  to  5,  as  has  been  hitherto  accepted  in  the  case  of  Fehling.  If 
well  stoppered  it  keeps  perfectly. 

The  experiments  of  Hehner  (C.  N.  xxxix.  197)  and  Yoshida 
(C.  N.  xliii.  29),  as  also  my  own,  show  that  the  ratio  of  reduction 
is  seriously  influenced  by  the  amount  of  fixed  caustic  alkali  in  the 
solution  and  by  the  strength  of  the  ammonia,  consequently  the 
result  can  only  be  depended  on  when  the  solution  is  standardized 
under  precisely  the  same  conditions  as  are  adopted  in  the  actual 
analysis.  The  variations  with  sugars,  other  than  dextrose,  appear 
to  be  even  greater  than  occur  in  the  usual  Fehling  process. 

In  order  to  avoid  the  nuisance  of  filling  the  laboratory  with 
strong  ammoniacal  vapours,  the  titration  should  be  made  in  a  small 
boiling  flask,  through  the  cork  of  which  the  elongated  end  of  the 
burette  is  passed.  A  small  escape  tube  is  also  passed  through  the 
same  cork,  leading  into  a  vessel  containing  water  or  weak  acid,  in 
order  to  condense  the  ammonia.  The  titration  should  in  all  cases 
be  made  as  quickly  as  possible. 

Stillingfleet  Johnson  (C.  N.  xlvii.  57)  points  out  that  in  this  process 
it  is  possible  to  verify  the  results  of  titration  on  one  and  the  same  portion  of 
cupric  solution,  by  passing  air  in  sufficient  volume  through  the  liquid  to 
re-oxidize  the  reduced  copper  to  the  blue  cupric  state. 

In  carrying  out  this  arrangement  it  is  necessary  to  use  a  wide-mouthed 
boiling  flask  having  a  cork  with  three  holes— one  for  the  burette  spit,  one  for 
the  escape  tube,  and  the  other  carrying  a  tube  reaching  to  the  bottom  of  the 
flask,  and  to  which  is  attached  a  Dancer's  aspirator.  About  H  liter  of  air 
passed  through  in  fifteen  minutes  suffices  to  restore  the  full  colour,  the  liquid 
being  kept  boiling  the  whole  time.  It  is  hardly  necessary  to  say  that  a  larger 
excess  than  usual  of  NH3  must  be  used  in  order  to  prevent  precipitation  of 
Cu2O  by  loss  on  long  boiling.  This,  it  appears  to  me,  is  a  serious  drawback 
in  point  of  accuracy,  because  the  conditions  of  titration  cannot  be  the  same. 

The  method  is  well  adapted  for  the  examination  of  diabetic 
urine  and  milk,  also  mixtures  of  milk  and  cane  sugars,  and 
certainly  has  the  advantage  over  the  ordinary  Fehling  method  by 
its  definite  end-action. 


304  VOLUMETRIC   ANALYSIS.  §    VI. 

Some   technical  applications   of  these   Solutions   for   mixtures   of 
various   Sugars. 

It  cannot  be  claimed  for  these  estimations  that  they  are  absolutely 
exact ;  but  with  care  and  practice,  accompanied  with  uniform  con- 
ditions, they  are  probably  capable  of  the  best  possible  results 
whatever  methods  may  be  used. 

Cane  Sugar,  Grape  Sugrar,  and  Dextrine  (Biard  and  Pellet, 
Z.  a.  C.  xxiv.  275).  The  solution  containing  these  three  forms  is  first 
titrated  with  the  usual  Fehling  solution  for  grape  sugar.  A  second  portion 
is  boiled  with  acetic  acid  (which  only  inverts  cane  sugar)  and  titrated. 
Finally,  a  third  portion  is  completely  inverted  with  sulphuric  acid  and 
titrated.  The  difference  of  the  first  and  second  titrations  gives  the  cane 
sugar,  and  that  of  the  second  and  third  the  dextrine. 

Milk  and  Cane  Sugar. — If  the  estimation  of  milk  sugar  is  alone  re- 
quired, and  by  the  usual  Fehling  solution,  the  casein  and  albumen  must 
be  first  removed.  Acidify  the  liquid  with  a  few  drops  of  acetic  acid,  warm 
until  coagulation  is  effected,  and  filter.  Boil  the  filtrate  to  coagulate  the 
albumen.  Filter  again,  and  neutralize  with  soda  previous  to  treatment  for 
sugar  by  the  copper  test.  The  number  of  c.c.  of  Fehling's  solution  re- 
quired, multiplied  by  0 '006786,  will  give  the  weight  of  milk  sugar  in 
grams.  Direct  estimation  by  Pavy-Fehling  is  preferable  to  this  method. 
Cane  sugar  in  presence  of  milk  sugar  may  be  estimated  as  follows : — Dilute 
the  milk  to  ten  times  its  bulk,  having  previously  coagulated  it  with  a  little 
citric  acid,  filter,  and  make  up  to  a  definite  volume,  titrate  a  portion  with 
Pavy-Fehling  solution,  and  note  the  result.  Then  take  100  c.c.  of  the 
filtrate,  add  2  gm.  of  citric  acid,  and  boil  for  10  minutes,  cool,  neutralize, 
make  up  to  200  c.c.,  and  titrate  with  copper  solution  as  before.  The  difference 
between  the  reducing  powers  of  the  solutions  before  and  after  conversion  is 
due  to  the  cane  sugar,  the  milk  sugar  not  being  affected  by  citric  acid. 

Stokes  and  Bodmer  (Analyst,  x.  62)  have  experimented  largely  on  this 
method,  and  with  satisfactory  results.  The  plan  adopted  by  them  is  to  use 
40  c.c.  of  Pavy-Fehling  liquid  (=0'02  gm.  glucose),  and  to  dilute  the 
sugar  solution  (without  previous  coagulation),  so  that  from  6  to  12  c.c.  are 
required  for  reduction.  By  using  a  screw-clamp  on  the  rubber  burette  tube, 
the  sugar  solution  is  allowed  to  drop  into  the  boiling  liquid  at  a  moderate 
rate.  If  Cu2O  should  be  precipitated  before  the  colour  disappears,  a  fresh 
trial  must  be  made,  adding  the  bulk  of  the  sugar  at  once,  then  finishing  by 
drops.  If,  on  the  other  hand,  the  sugar  has  been  run  in  to  excess,  which 
owing  to  the  rather  slow  reaction  is  easily  done,  fresh  trial  must  be  again 
made  until  the  proper  point  is  reached :  this  gives  the  milk  sugar.  Mean- 
while a  portion  of  the  mixed  sugar  solution  is  boiled  with  2  per  cent,  of 
citric  acid,  neutralized  with  NH3,  made  up  to  double  its  original  volume,  and 
titrated  as  bdfore. 

These  operators  have  determined  the  reducing  action  of  milk, 
cane,  and  grape  sugar  on  the  Pavy-Fehling  liquid,  the  result 
being  that  100  lactose  represents  respectively  52  glucose,  or  49 '4 
sucrose. 

The  Pavy-Fehling  liquid  is  admirably  adapted  for  the  esti- 
mation of  lactose  in  milk  direct  after  dilution,  no  coagulation  being 
necessary. 


§  72.  SULPHUR.  305 

SULPHUR. 

S  =  32. 

Estimation    in    Pyrites,    Ores,    Residues,    etc. 
1.    Alkalimetric    Method    (Pelouze). 

§  72.  THIS  process,  designed  for  the  rapid  estimation  of  sulphur 
in  iron  and  copper  pyrites,  has  hitherto  been  thought  tolerably 
accurate,  but  experience  has  shown  that  it  cannot  be  relied  upon 
except  for  rough  technical  purposes. 

The  process  is  based  on  the  fact,  that  when  a  sulphide  is  ignited 
with  potassic  chlorate  and  sodic  carbonate,  the  sulphur  is  converted 
entirely  into  sulphuric  acid,  which  expels  its  equivalent  proportion 
of  carbonic  acid  from  the  soda,  forming  neutral  sodic  sulphate ;  if 
therefore,  an  accurately  weighed  quantity  of  the  substance  be 
fused  with  a  known  weight  of  pure  sodic  carbonate  in  excess,  and 
the  resulting  mass  titrated  with  normal  acid,  to  find  the  quantity 
of  unaltered  carbonate,  the  proportion  of  sulphur  is  readily 
calculated  from  the  difference  between  the  volume  of  normal  acid 
required  to  saturate  the  original  carbonate,  and  that  actually 
required  after  the  ignition. 

It  is  advisable  to  take  1  gm.  of  the  finely  levigated  pyrites,  and 
5 '3  gm.  of  pure  sodic  carbonate  for  each  assay;  and  as  5 '3  gm.  of 
sodic  carbonate  represent  100  c.c.  of  normal  sulphuric  acid,  it  is 
only  necessary  to  subtract  the  number  of  c.c.  used  after  the  ignition 
from  100,  and  multiply  the  remainder  by  0*016,  in  order  to  arrive 
at  the  weight  of  sulphur  in  the  1  gm.  of  pyrites,  and  by  moving 
the  decimal  point  two  places  to  the  right,  the  percentage  is  obtained. 

Example :  1  gm.  of  finely  ground  PeS2  was  mixed  intimately  with  5'3  gin- 
sodic  carbonate,  and  about  7  gm.  each  of  potassic  chlorate,  and  decrepitated 
sodic  chloride,  in  powder ;  then  introduced  into  a  platinum  crucible,  and 
gradually  exposed  to  a  dull  red  heat  for  ten  minutes ;  the  crucible  suffered 
to  cool,  and  warm  water  added  ;  the  solution  so  obtained  was  brought  on  a 
moistened  filter,  the  residue  emptied  into  a  beaker  and  boiled  with  a  large 
quantity  of  water,  brought  on  the  filter,  and  washed  with  boiling  water  till 
all  soluble  matter  was  removed ;  the  filtrate  coloured  with  methyl  orange, 
and  titrated.  67  c.c.  of  normal  acid  were  required,  which  deducted  from  100, 
left  33  c.c. ;  this  multiplied  by  0'016  gave  0'528  gm.  or  52'8  per  cent.  S. 

The  most  satisfactory  method  of  estimating  the  sulphur  in 
pyrites  used  for  the  manufacture  of  sulphuric  acid,  is  the 
gravimetric  one  by  Lunge,  and  which  consists  in  treating  the 
finely  divided  ore  with  aqua-rer/ia,  evaporating  to  dryness,  expelling 
HNO3  by  HC1,  removing  Fe  from  the  solution  by  ammonia,  then 
precipitating  the  sulphur  as  baric  sulphate.  Full  details  are 
given  in  the  Alkali  Maker's  Pocket  Book. 

Burnt  Pyrites. — The  only  satisfactory  volumetric  method  of 
estimating  the  sulphur  in  the  residual  ores  of  pyrites,  is  that 
described  by  Watson  (/.  S.  C.  I.  vii.  305),  and  which  is  in  daily 


306  VOLUMETRIC  ANALYSIS.  §    72. 

use  in  large  alkali  works.  In  order  to  avoid  calculation,  Watson 
adopts  the  following  method  : — 

Standard  Hydrochloric  Acid.— 1  c.c.  =  0'02  gm.  Xa20. 

Sodic  bicarbonate. — This  may  be  the  ordinary  commercial  salt, 
but  its  exact  alkalinity  must  be  ascertained  by  the  standard  acid. 
Where  a  number  of  analyses  are  being  made,  a  good  quantity  of 
the  salt  should  be  well  mixed,  and  kept  in  a  stoppered  bottle.  Its 
exact  alkalinity  having  been  once  determined  it  will  not  alter, 
though  daily  opened. 

The  Analysis :  2  gm.  of  bicarbonate  is  placed  in  a  crucible  which  may  be 
either  of  platinum,  porcelain,  or  nickel,  and  to  it  is  added  5' 16  gm.  of  the 
finely  powdered  ore,  then  intimately  mixed  with  a  flattened  glass  rod. 
Heat  gently  over  a  Bunsen  burner  for  5  or  10  minutes,  and  break  up  the 
mass  with  a  stout  copper  wire.  After  stirring,  the  heat  is  increased  and 
continued  for  10  or  15  minutes.  The  crucible  is  then  washed  out  with  hot 
water  into  a  beaker.  The  mixture  is  boiled  for  15  minutes,  filtered  into  a  flask, 
the  residue  washed  repeatedly  with  hot  water,  then  cooled  and  titrated  with 
the  standard  acid,  using  methyl  orange  as  indicator. 

Example :  2  gm.  of  the  bicarbonate  originally  required  37'5  c.c.  of  acid. 
After  ignition  with  the  ore,  28  c.c.  were  required  =9*5  c.c.,  this  divided  by 
5  will  give  1'9,  which  is  the  percentage  of  total  sulphur  in  the  ore. 

This  total  sulphur  includes  that  which  exists  as  soluble  sulphide, 
and  which  is  not  available  for  acid  making.  In  order  to  find  the 
amount  of  this  soluble  sulphur,  Watson  boils  5 '16  gm.  of  the  ore 
with  5  c.c.  of  standard  sodic  carbonate  (1  c.c.  =  0'05gm.  Na20) 
diluted  with  water,  for  15  minutes.  After  filtering  and  washing, 
the  filtrate  is  titrated  with  the  standard  hydrochloric  acid,  and  the 
difference  between  the  volume  used  and  that  which  was  originally 
required  for  5  c.c.  of  the  soda  solution  is  divided  by  5,  as  in  the 
case  of  the  former  process,  which  gives  at  once  the  percentage  of 
sulphur  existing  in  the  ore  in  a  soluble  form.  The  results  are 
not  absolutely  exact,  but  quite  near  enough  to  guide  a  manufacturer 
in  the  working  of  the  furnaces. 

This  method  is  not  available  for  green  pyrites. 


2.     Estimation    of   Sulphur    in    Coal    G-as. 

A  most  convenient  and  accurate  process  for  this  estimation  is 
that  of  Wildenstein(§73.2).  The  liquid  produced  by  burning 
the  measured  gas  in  a  Letheby  or  Vernon  Harcourt  apparatus 
is  well  mixed,  and  brought  to  a  definite  volume ;  a  portion  repre- 
senting a  known  number  of  cubic  feet  of  gas  is  then  poured  into  a 
glass,  porcelain,  or  platinum  basin,  acidified  slightly  with  HC1, 
heated  to  boiling,  and  a  measured  excess  of  standard  baric  chloride 
added;  the  excess  of  acid  is  then  cautiously  neutralized  with 
ammonia  (free  from  carbonate),  and  the  excess  of  barium  ascer- 
tained by  standard  potassic  chromate  exactly  as  described  in 
S  73.2. 


§  72.  SULPHUR.  307 

The  usual  method  of  stating  results  is  in  grains  of  sulphur  per 
100  cubic  feet  of  gas.  This  may  be  done  very  readily  by  using 
semi-normal  solutions  of  baric  chloride  and  potassic  chromate  on 
the  metric  system,  and  multiplying  the  number  of  c.c.  of  baric 
solution  required  with  the  factor  0'1234,  which  at  once  gives  the 
amount  of  sulphur  in  grains. 

Standard  solutions  can  of  course  be  made  in  the  same  manner 
on  the  grain  system. 


3.      Estimation    of   Sulphur    in.    Sulphides    decomposable    by 
Hydrochloric    or    Sulphuric    Acids    (Weil). 

This  process,  communicated  to  me  by  M.  Weil,  is  based  on  the 
fact  that,  in  the  case  of  sulphides  where  the  whole  of  the  sulphur 
is  given  off  as  H2S  by  heating  with  HC1  or  H2S04,  the  IPS  may 
be  evolved  into  an  excess  of  a  standard  alkaline  copper  solution. 
After  the  action  is  complete,  the  amount  of  Cu  left  unreduced  is 
estimated  by  standard  stannous  chloride.  The  method  is  available 
for  the  sulphides  of  lead,  antimony,  zinc,  iron,  etc.  Operators 
should  consult  and  practise  the  methods  described  in  §  54.6,  in 
order  to  become  accustomed  to  the  special  reaction  involved. 

The  Analysis :  From  1  to  10  gin.  of  material  (according  to  its  richness  in 
sulphur)  in  the  finest  state  of  division,  are  put  into  a  long  necked  flask  of 
about  200  c.c.  capacity,  to  which  is  fitted  a  bent  delivery  tube,  so  arranged  as 
to  dip  to  the  bottom  of  a  tall  cylinder,  containing  50  or  100  c.c.  of  standard 
copper  solution  made  by  dissolving  39' 523  gm.  of  cupric  sulphate,  200  gm. 
of  Rochelle  salt  and  125  gm.  of  pure  caustic  soda  in  water,  and  diluting  to 
1  liter  (10  c.c.=0'l  gm.  Cu).  When  this  is  ready,  a  few  pieces  of  granulated 
zinc  are  added  to  the  sulphide.  75  c.c.  of  strong  HC1  are  then  poured  over 
them,  the  cork  with  delivery  tube  immediately  inserted,  connected  with  the 
copper  solution,  and  the  flask  heated  on  a  sand-bath  until  all  evolution  of 
H'2S  is  ended.  The  blue  solution  and  black  precipitate  are  then  brought  on 
a  filter,  filtrate  and  washings  collected  in  a  200  or  250  c.c.  flask,  and  diluted 
to  the  mark ;  20  c.c.  of  the  clear  blue  liquid  are  then  measured  into  a  boiling 
flask,  and  evaporated  to  10  or  15  c.c.  25  to  50  c.c.  of  strong  HC1  are  then 
added,  and  the  standard  tin  solution  dropped  in  while  boiling,  until  the  blue 
gives  place  to  a  clear  pure  yellow. 

Each  c.c.  of  standard  copper  solution  represents  0'50393  gm. 
sulphur.  The  addition  of  the  granulated  zinc  facilitates  the 
liberation  of  the  H2S,  and  sweeps  it  out  of  the  flask ;  moreover, 
in  the  case  of  dealing  with  lead  sulphide,  which  forms  insoluble 
lead  chloride,  it  materially  assists  the  decomposition.  Alkaline 
tartrate  solution  of  copper  may  be  used  in  place  of  ammoniacal 
solution  if  so  desired. 

Examples  (Weil) :  1  gm.  of  galena  was  taken,  and  the  gas  delivered  into 
50  c.c.  of  standard  copper  solution  (=0'5  gm.  Cu).  After  complete  pre- 
cipitation the  blue  liquid  was  diluted  to  200  c.c.  20  c.c.  of  this  required 
12'5  c.c.  of  stannous  chloride,  the  titre  of  which  was  16'5  c.c.  for  0'04  gm. 
Cu.  Therefore  16'5  :  0'04  ::  12-5  :  0'0303.  Thus  200  c.c.  (  =  1  gm.  galena) 
represent  0'303  gm.  Cu.  Then  0'5  gm.  Cu,  less  0'303=0'197  gm,  for  1  gm. 

x  2 


308  VOLUMETRIC   ANALYSIS.  §    72. 

galena  or  197  for  100  gm.  Consequently  197  x  0'50393=9'92  per  cent.  S. 
Estimation  by  weight  gave  9'85  per  cent.  Again,  1  gni.  zinc  sulphide  was 
taken  with  100  c.c.  copper  solution  and  made  up  to  250  c.c.,  25  c.c.  of  which 
required  14'3  c.c.  of  same  stannous  chloride,  or  143  c.c.  for  the  1  gm. 
sulphide.  This  represents  0'347  gm.  Cu.  Thus  1—0'347 =0'653  gm.  Cu 
(precipitated  as  CuS)  or  65'3  per  100.  Consequently  65'3  x  0' 50393=32  9 
per  cent.  S.  Control  estimation  by  weight  gave  33  per  cent. 

The  process  has  given  me  good  technical  results  with  Sb2S3,  but 
the  proportion  of  sulphur  to  copper  is  too  great  to  expect  strict 
accuracy. 


4.    Estimation  of  Alkaline  Sulphides  by  Standard  Zinc  Solution. 

This  method,  which  is  simply  a  counterpart  of  §  78.3,  is 
especially  applicable  for  the  technical  determination  of  alkaline 
sulphides  in  impure  alkalies,  mother-liquors,  etc. 

If  the  zinc  solution  be  made  by  dissolving  3 '253  gm.  of  pure 
metallic  zinc  in  hydrochloric  acid,  supersaturating  with  ammonia, 
and  diluting  to  1  liter,  or  32*53  grn.  to  1000  dm.,  1  c.c.  or  dm. 
will  respectively  indicate — 

0-0016  gm.  or  0'016  grn.  Sulphur 
0-0039     „          0-039     „     Sodic  sulphide 
0-00551  „          0-0551  „     Potassic  sulphide 
0-0034     „          0-034     „     Ammonic  sulphide. 

The  zinc  solution  is  added  from  a  burette  until  no  dark  colour  is 
shown,  when  a  drop  is  brought  in  contact  with  solution  of  nickel 
protochloride  spread  in  drops  on  a  white  porcelain  tile. 


5.      Sulphurous    Acid    and    Sulphites. 

The  difficulties  formerly  presented  in  the  iodometric  analyses  of 
these  substances  are  now  fortunately  quite  overcome  by  the 
modification  devised  by  Giles  and  Shearer  (J.  S.  G.  I.  iii.  197 
and  iv.  303).  A  valuable  series  of  experiments  on  the  estimation 
of  SO2,  either  free  or  combined,  are  detailed  in  these  papers.  The 
modification  is  both  simple  and  exact,  and  consists  in  adding  the 
weighed  SO2  or  the  sulphite  in  powder  to  a  measured  excess 
of  YQ-  iodine  without  dilution  with  water,  and  when  the  decomposi- 
tion is  complete,  titrating  back  with  ~^  thiosulphate.  Very  con- 
centrated _  solutions  of  SO2  are  cooled  by  a  freezing  mixture,  and 
enclosed  in  thin  bulbs,  which  can  be  broken  under  the  iodine 
solution :  this  is,  however,  not  required  with  the  ordinary  pre- 
parations. Sulphites  and  bisulphites  of  the  alkalies  and  alkaline 
earths,  also  zinc  and  aluminium,  may  all  be  titrated  in  this  way 
with  accuracy;  the  less  soluble  salts,  of  course,  requiring  more 
time  and  agitation  to  ensure  their  decomposition.  A  preliminary 
titration  is  first  made  with  a  considerable  excess  of  iodine,  and 


§  72.  SULPHUR.  309 

a  second  with  a  more  moderate  excess  as  indicated  by  the  first 
trial.  1  c.c.  ^  iodine  =  0-0032  gni.  SO2. 

The  authors  found  that  when  perfectly  pure  iodine  and  neutral 
potassic  iodide  were  used  for  the  standard  solution,  its  strength 
remained  intact  for  a  long  period  ;  and  the  same  with  the 
thiosulphate,  if  the  addition  of  about  2  gin.  of  potassic  bicarbonate 
to  the  liter  was  made,  and  the  stock  solution  kept  in  the  dark  (see 
page  116). 

From  a  large  number  of  experiments,  they  also  deduced  the 
simple  law  of  the  ratio  between  any  given  percentage  of  SO2 
in  aqueous  solution  at  15  '4°  and  760  m.ni.,  and  its  specific  gravity; 
namely,  the  percentage  found  by  titration  multiplied  by  0'005 
and  added  to  unity  gives  the  sp.  gr. 

6.      Estimation    of    Mixtures    of   Alkaline    Sulphides,    Sulphites, 
and    Thiosulphates. 

Lunge  and  Smith  (J.  S.  C.  I.  ii.  463)  have  established  the 
fact,  that  both  sulphites  and  thiosulphates  may  be  completely 
oxidized  to  sulphates,  by  treating  them  with  a  large  excess  of 
standard  permanganate,  more  than  sufficient  for  complete  oxidation 
and  formation  of  MnO2.  An  excess  of  standard  ferrous  sulphate 
is  added,  then  titrated  back  with  permanganate  to  the  pink  colour. 
Upon  this  reaction,  together  with  the  known  accurate  estimation  of 
both  of  these  compounds  by  iodine,  in  the  absence  of  nitrates  and 
nitrites  or  other  similar  oxidizing  bodies,  they  have  founded  a  new 
and  ra.pid  volumetric  method,  which  gives  the  respective  proportions 
of  each  substance  when  occurring  together.  If  sulphides  are  also 
present,  their  amount  is  first  ascertained  separately  with  standard 
ammoniacal  zinc  chloride.  The  whole  of  the  three  compounds 
might  be  oxidized  by  permanganate  if  so  chosen,  and  the  sulphide 
found  by  difference,  but  the  separation  is  said  to  be  better. 

The  process  consists  of  two  titrations  ;  one  with  standard  iodine 
and  the  other  with  standard  permanganate,  adding  the  latter  in 
large  excess  to  the  slightly  alkaline  or  neutral  solution,  then 
acidifying  with  H2S04,  titrating  back  with  excess  of  standard 
FeSO4,  and  finishing  with  permanganate. 

The  following  equations  represent  the  action  of  the  permanganate 
and  iodine  respectively  :  — 


(1)  Xa2S203  +  202  +  H20  =  :NTa2S04  +  H2S04. 

(2)  4Xa2S03  +  202  =  4Xa2S04. 

(3)  2Xa2S203  +  12  =  Na2S40«  +  2KaL 

(4)  ]STa2S03  +  12  +  H20  =  2sTa2S04  +  2HI. 

Let  W  equal  the  weight  of  sulphur  as  thiosulphate  oxidized  to 
sulphate  by  1  c.c.  of  KMnO4  solution.  Let  W1  equal  the  weight 
of  sulphur  as  thiosulphate  acted  on  by  1  c.c.  of  iodine  solution. 
Then  it  is  evident  from  the  above  equations  that  2W  is  the  weight 


310  VOLUMETKIC   ANALYSIS.  §    73. 

of  sulphur  as  sulphite  oxidized  by  1   c.c.  of  KMnO4  and  —  —  that 

oxidized  by  1  c.c.  of  iodine.  In  the  given  mixture  let  S  =  weight 
of  sulphur  present  as  thiosulphate  and  s  =  ditto  as  sulphite,  K"  = 
number  of  c.c.  KMnO4  and  N1  =  ditto  of  iodine  required. 

Then  :_         _ 


or  2S  +  *  =  2WM"  (1) 

and  W  +  W  =  ^ 

or  S  +  ^-W1^1  (2) 

8S  +  4»  =  8WN  (la) 

(la)—  (2)         7S  =  8WN  - 


-  2S  =  2WN  -  1(8  WX  -  W1^1)  (II) 


An  advantage  in  point  of  accuracy  arises  from  the  fact  that  a 
unit  weight  of  sulphur  as  thiosulphate  requires  twice  the  amount 
of  KMnO4,  but  only  one-fourth  the  amount  of  I,  that  a  unit  of 
sulphur  as  sulphite  requires.  The  permanganate  method  is  there- 
fore more  accurate  for  an  estimation  of  the  former  and  the  iodine 
for  the  latter.  In  a  mixture  of  the  two,  the  experimental  errors 
tend  to  counteract  each  other. 

The  estimation  of  nitrites  in  the  presence  of  sulphites  and 
thiosulphates  has  been  described  in  §  67. 

Davis  has  devised  also  a  method  of  titrating  mixtures  of 
sulphides,  sulphites,  and  thiosulphates  (/.  £  C.  I.  i.  88). 


SULPHURIC    ACID    AND    SULPHATES. 

Monohydrated    Sulphuric    Acid. 

H2S04=98. 

Sulphuric    Anhydride. 

SO3  =  80. 
1.  Mohr's  Method. 

§  73.  THE  indirect  process  devised  by  C.  Mohr  (Ann.  der 
Chem.  u.  Pliarm.  xc.  165)  consists  in  adding  a  known  volume  of 
baric  solution  to  the  compound,  more  than  sufficient  to  precipitate 
the  SO3.  The  excess  of  barium  is  converted  into  carbonate,  and 
titrated  with  normal  acid  and  alkali.* 

Normal   Baric   chloride  is  made  by  dissolving  121 '7  7  gin.   of 

*  Gawalowski  (Z.  a.  C.  xxvii.  152)  advocates  a  simplification  of  this  method  by 
titrating  the  excess  of  barium  with  standard  sodic  carbonate,  using  pheriolphthalein 
as  indicator,  but  the  results  in  my  hands  have  proved  very  unsatisfactory. 


§    73.  SULPHURIC   ACID.  311 

pure  crystals  of  baric  chloride  in  the  liter ;  this  solution  likewise 
suffices  for  the  determination  of  SO3  by  the  direct  method. 
The  following  is  the  method  of  procedure. 

If  the  substance  contains  a  considerable  quantity  of  free  acid,  it  must  be 
brought  near  to  neutrality  by  pure  sodic  carbonate;  if  alkaline,  slightly 
acidified  with  hydrochloric  acid ;  a  round  number  of  c.c.  of  barium  solution  in 
excess  is  then  added,  and  the  whole  digested  in  a  warm  place  for  some  minutes ; 
the  excess  of  barium  is  precipitated  by  a  mixture  of  carbonate  and  caustic 
ammonia  in  slight  excess ;  if  a  piece  of  litmus  paper  be  thrown  into  the 
mixture,  a  great  excess  may  readily  be  avoided.  The  precipitate  containing 
both  sulphate  and  carbonate  is  now  to  be  collected  on  a  filter,  thoroughly 
washed  with  boiling  water,  and  titrated. 

The  difference  between  the  number  of  c.c.  of  barium  solution 
added,  and  that  of  normal  acid  required  for  the  carbonate,  will  be 
the  measure  of  the  sulphuric  acid  present;  each  c.c.  of  barium 
solution  is  equal  to  0'040  gm.  SO3. 

Example :  2  gm.  of  pure  and  dry  baric  nitrate,  and  1  gm.  of  pure  potassic 
sulphate  were  dissolved,  mixed,  and  precipitated  hot  with  carbonate  and 
caustic  ammonia ;  the  precipitate,  after  being  thoroughly  washed,  gave 
1'002  gm.  potassic  sulphate,  instead  of  1  gm. 

For  technical  purposes  this  process  may  be  considerably  shortened 
by  the  following  modification,  which  dispenses  with  the  washing  of 
the  precipitate. 

The  solution  containing  the  sulphates  or  sulphuric  acid  is  first  rendered 
neutral ;  normal  baric  chloride  is  then  added  ,in  excess,  then  normal  sodic 
carbonate  in  excess  of  the  baric  chloride,  and  the  volume  of  both  solutions 
noted  ;  the  liquid  is  then  made  up  to  200  or  300  c.c.  in  a  flask,  and  an  aliquot 
portion  filtered  off  and  titrated  with  normal  acid.  The  difference  between 
the  baric  chloride  and  sodic  carbonate  gives  the  sulphuric  acid. 

The  solution  must  of  course  contain  no  substance  precipitable  by 
sodic  carbonate  except  barium  (or  if  so,  it  must  be  previously 
removed) ;  nor  must  it  contain  any  substance  precipitable  by 
barium,  such  as  phosphoric  or  oxalic  acid,  etc. 

Another  alkalimetric  process  suitable  for  technical  purposes  is 
that  of  Bohlig  (§  28),  also  Grossmann  (§  16.14). 


2.      Titration    by    Baric    Chloride    and    Potassic    Chromate 
(Wildenstein). 

To  the  hot  solution  containing  the  SO3  to  be  estimated  (which 
must  be  neutral,  or  if  acid,  neutralized  with  caustic  ammonia,  free 
from  carbonate),  a  standard  solution  of  baric  chloride  is  added  in 
slight  excess,  then  a  solution  of  potassic  chromate  of  known 
strength  is  cautiously  added  to  precipitate  the  excess  of  barium. 
So  long  as  any  barium  remains  in  excess,  the  supernatant  liquid  is 
colourless ;  when  it  is  all  precipitated  the  liquid  is  yellow,  from  the 
free  chromate;  a  few  drops  only  of  the  chromate  solution  are 
necessary  to  produce  a  distinct  colour. 


312  VOLUMETRIC  ANALYSIS.  §    73. 

Wildenstein  uses  a  baric  solution,  of  which  1  c.c.  =  0*015 
gin.  of  SO3,  and  chromate  1  c.c.  =  0*010  gm.  of  SO3.  I  prefer 
to  use  §•  solutions,  so  that  1  c.c.  of  each  is  equal  to  0*02  gm. 
of  SO3.  If  the  chromate  solution  is  made  equal  to  the  baric 
chloride,  the  operator  has  simply  to  deduct  the  one  from  the  other, 
in  order  to  obtain  the  quantity  of  baric  solution  really  required  to 
precipitate  all  the  SO3. 

The  Analysis :  The  substance  or  solution  containing  SO3  is  brought  into 
a  small  flask,  diluted  to  about  50  c.c.,  acidified  if  necessary  with  HC1,  heated 
to  boiling,  and  precipitated  with  a  slight  excess  of  standard  baric  chloride 
delivered  from  the  burette.  As  the  precipitate  rapidly  settles  from  a  boiling 
solution,  it  is  easy  to  avoid  any  great  excess  of  barium,  which  would  prevent 
the  liquid  from  clearing  so  speedily.  The  mixture  is  then  cautiously 
neutralized  with  ammonia  free  from  carbonic  acid  (to  be  certain  of  this,  it  is 
well  to  add  to  it  two  or  three  drops  of  calcic  chloride  or  acetate  solution). 

The  flask  is  then  heated  to  boiling,  and  the  chromate  solution  added  in 
i  c.c.  or  so,  each  time  removing  the  flask  from  the  heat  and  allowing  to 
settle,  until  the  liquid  is  of  a  light  yellow  colour ;  the  quantity  of  chromate 
is  then  deducted  from  the  barium  solution,  and  the  remainder  calculated 
for  SO3. 

Or  the  mixture  with  barium  in  excess  may  be  diluted  to  100  or  150  c.c., 
the  precipitate  allowed  to  settle  thoroughly,  and  25  or  50  c.c.  of  the  clear 
liquid  heated  to  boiling,  after  neutralizing,  and  precipitated  with  chromate 
until  all  the  barium  is  carried  down  as  baric  chromate,  leaving  the  liquid  of 
a  light  yellow  colour ;  the  analysis  should  be  checked  by  a  second  titration. 
The  process  has  yielded  me  very  satisfactory  results  in  comparison  with  the 
barium  method  by  weight ;  it  is  peculiarly  adapted  for  estimating  sulphur  in 
gas  when  burnt  in  the  Letheby  sulphur  apparatus,  details  of  .which  will  be 
found  on  page  306. 

The  presence  of  alkaline  and  earthy  salts  is  of  no  consequence — 
Zn  and  Cd  do  not  interfere — M,  Co,  and  Cu  give  coloured 
solutions  which  prevent  the  yellow  chromate  being  seen,  but  this 
difficulty  can  be  overcome  by  the  use  of  an  external  indicator  for 
the  excess  of  chromate.  This  indicator  is  an  ammoniacal  lead 
solution,  made  by  mixing  together,  at  the  time  required,  one 
volume  of  pure  ammonia  and  four  volumes  of  lead  acetate  solution 
(1  :  20).  The  liquid  has  an  opalescent  appearance.  To  use  the 
indicator,  a  large  drop  is  spread  upon  a  white  porcelain  plate,  and 
one  or  two  drops  of  the  liquid  under  titration  added;  if  the 
reddish-yellow  colour  of  lead  chromate  is  produced,  there  is  an 
excess  of  chromate,  which  can  be  cautiously  reduced  by  adding 
more  barium  until  the  exact  balance  occurs. 

Precht  (Z.  a.  C.  1879,  521)  modifies  this  process  by  precipitating 
the  SO3  with  excess  of  standard  baric  chloride,  which  excess  is 
removed  by  standard  potassic  chromate  also  in  excess,  which  latter 
is  in  turn  estimated  by  weak  standard  ferrous  sulphate,  the  end  of 
the  reaction  being  found  by  spotting  the  liquid  on  a  white  plate 
with  potassic  ferricyanide. 

I  can  see  no  advantage  in  this  modification,  and  in  many  cases  it 
would  be  totally  inadmissible,  owing  to  the  presence  of  substances 
affecting  the  ferrous  reagent 


§73.  SULPHURIC    ACID.  313 

3.     Direct   Precipitation   with   Normal   Baric   Chloride. 

Very  good  results  may  be  obtained  by  this  method  when 
carefully  performed. 

The  substance  in  solution  is  to  be  acidified  with  hydrochloric  acid,  heated 
to  boiling,  and  the  baric  solution  allowed  to  flow  cautiously  in  from,  the 
burette  until  no  further  precipitation  occurs.  The  end  of  the  process  can 
only  be  determined  by  filtering  a  portion  of  the  liquid,  and  testing  with 
a  drop  of  the  baric  solution.  "Beale's  filter  (shown  in  fig.  19)  is  a  good  aid 
in  this  case.  A  few  drops  of  clear  liquid  are  poured  into  a  test  tube  and  a 
drop  of  baric  solution  added  from  the  burette ;  if  a  cloudiness  occurs,  the 
contents  of  the  tubes  must  be  emptied  back  again,  washed  out  into  the 
liquid,  and  more  baric  solution  added  until  all  the  SO3  is  precipitated.  It  is 
advisable  to  use  T^  solution  towards  the  end  of  the  process. 

Instead  of  the  test  tube  for  finding  whether  barium  or  sulphuric 
acid  is  in  excess,  a  plate  of  black  glass  may  be  used,  on  which  a  drop 
of  the  clear  solution  is  placed  and  tested  by  either  a  drop  of  baric 
chloride  or  soclic  sulphate, — these  testing  solutions  are  preferably 
kept  in  two  small  bottles  with  elongated  stoppers.  A  still  better 
plan  is  to  spot  the  liquids  on  a  small  mirror,  as  suggested  by 
Haddock  (C.  N.  xxxix.  156);  the  faintest  reaction  can  then  be 
seen,  although  the  liquid  may  be  highly  coloured. 

Wildenstein  has  arranged  another  method  for 
direct  precipitation,  especially  useful  where  a  con- 
stant  series  of  estimations  have  to  be  made.  The 
apparatus  is  shown  in  fig.  44.  A  is  a  bottle  of 
900  or  1000  c.c.  capacity,  with  the  bottom  removed, 
and  made  of  well-annealed  glass  so  as  to  stand 
heating;  E  a  thistle  funnel  bent  round,  as  in  the 
figure,  and  this  syphon  filter  is  put  into  action  by 
opening  the  pinch-cock  below  the  cork.  The  mouth 
<§  Q>  of  the  funnel  is  first  tied  over  with  a  piece  of  fine 

cotton  cloth,  then  two  thicknesses  of  Swedish  filter 
"  paper,  and  again  with  a  piece  of  cotton  cloth,  the 

whole  being  securely  tied  with  waxed  thread. 
In  precipitating  SO3  by  baric  chloride,  there  occurs  a  point 
similar  to  the  so-called  neutral  point  in  silver  assay,  when  in  one 
and  the  same  solution  both  barium  and  sulphuric  acid  after  a 
minute  or  two  produce  a  cloudiness.  Owing  to  this  circumstance, 
the  barium  solution  must  not  be  reckoned  exactly  by  its  amount 
of  Bad2,  but  by  its  Avorking  effect;  that  is  to  say,  the  process 
must  be  considered  ended  when  the  addition  of  a  drop  or  two  of 
barium  solution  gives  no  cloudiness  after  the  lapse  of  two  minutes. 

The  Analysis:  The  solution  containing  the  SO3  being  prepared,  and 
preferably  in  HC1,  the  vessel  A  is  filled  with  warm  distilled  water,  and  the 
pinch-cock  opened  so  as  to  fill  the  filter  to  the  bend  C ;  the  cock  is  then 
opened  and  shut  a  few  times  so  as  to  bring  the  water  further  down  into  the 
tube,  but  not  to  fill  it  entirely;  the  water  is  then  emptied  out  of  A,  and 
about  400  c.c.  of  boiled  distilled  water  poured  in  together  with  the  SO3 


314  VOLUMETRIC  ANALYSIS.  §    74. 

solution,  then,  if  necessary,  a  small  quantity  of  HC1  added,  and  the  baric 
chloride  added  in  moderate  quantity  from  a  burette.  After  mixing  well,  and 
waiting  a  few  minutes,  a  portion  is  drawn  off  into  a  small  beaker,  and  poured 
back  without  loss  into  A ;  a  small  quantity  is  then  drawn  off  into  a  test  tube, 
and  two  drops  of  baric  chloride  added.  So  long  as  a  precipitate  occurs,  the 
liquid  is  returned  to  A,  and  more  barium  added  until  a  test  is  taken  which 
shows  no  distinct  cloudiness ;  the  few  drops  added  to  produce  this  effect  are 
deducted.  If  a  distinct  excess  has  been  used,  the  analysis  must  be  corrected 
with  a  solution  of  SO3  corresponding  in  strength  to  the  barium  solution. 

A  simpler  and  even  more  serviceable  arrangement  of  apparatus 
on  the  above  plan  may  be  made,  by  using  as  the  boiling  and 
precipitating  vessel  an  ordinary  beaker  standing  on  wire  gauze  or 
a  hot  plate.  The  filter  is  made  by  taking  a  small  thistle  funnel,  tied 
over  as  described,  with  about  two  inches  of  its  tube,  over  which  is 
tightly  slipped  about  four  or  five  inches  of  elastic  tubing,  terminating 
with  a  short  piece  of  glass  tube  drawn  out  to  a  small  orifice  like  a 
pipette ;  a  small  pinch-cock  is  placed  across  the  elastic  tube  just 
above  the  pipette  end,  so  that  when  hung  over  the  edge  of  the 
beaker  with  the  funnel  below  the  surface  of  the  liquid,  the 
apparatus  will  act  as  a  syphon.  It  may  readily  be  filled  with  warm 
distilled  water  by  gentle  suction,  then  transferred  to  the  liquid 
under  titration.  By  its  means  much  smaller  and  more  concentrated 
liquids  may  be  used  for  the  analysis,  and  consequently  a  more 
distinct  evidence  of  the  reaction  obtained. 


SULPHURETTED    HYDROGEN. 

IPS  =  34. 

1  c.c.  YQ-  arsenious  solution  =  0'00255  gin.  H2S. 
1.     By   Arsenious   Acid    (Mohr). 

§  74.  THIS  residual  process  is  far  preferable  to  the  direct  titration 
of  sulphuretted  hydrogen  by  iodine.  The  principle  is  based  on  the 
fact,  that  when  H2S  is  brought  into  contact  with  an  excess  of 
arsenious  acid  in  hydrochloric  acid  solution,  arsenic  sulphide  is 
formed  ;  1  eq.  of  arsenious  acid  and  3  eq.  of  sulphuretted  hydrogen 
produce  1  eq.  of  arsenic  sulphide  and  3  eq.  of  water, 

As203  +  3H2S  =  As2S3  +  3H20. 

The  excess  of  arsenious  acid  used  is  found  by  --$  iodine  and  starch, 
as  in  §  36.  In  estimating  the  strength  of  sulphuretted  hydrogen 
water,  the  following  plan  may  be  pursued. 

A  measured  quantity,  say  10  c.c.,  of  /^  arsenious  solution  is  put  into  a 
300  c.c.  flask,  and  20  c.c.  of  sulphuretted  hydrogen  water  added,  well  mixed, 
and  sufficient  HC1  added  to  produce  a  distinct  acid  reaction ;  this  produces  a 
precipitate  of  arsenic  sulphide,  and  the  liquid  itself  is  colourless.  The  whole 
is  then  diluted  to  300  c.c.,  filtered  through  a  dry  filter  into  a  dry  vessel, 
100  c.c.  of  the  filtrate  taken  out  and  neutralized  with  sodic  bicarbonate,  then 


§    74  SULPHURETTED   HYDKOGEN. 

titrated  with  ^  iodine  and  starch.  The  quantity  of  arsenious  acid  so  found 
is  deducted  from  the  original  10  c.c.,  and  the  remainder  multiplied  by  the 
requisite  factor  for  H2S. 

The  estimation  of  H2S  contained  in  coal  gas,  may  by  this 
method  be  made  very  accurately  by  leading  the  gas  very  slowly 
through  the  arsenious  solution,  or  still  better,  through  a  dilute 
solution  of  caustic  alkali,  then  adding  arsenious  solution,  and 
titrating  as  before  described.  The  apparatus  devised  by  Mohr  for 
this  purpose  is  arranged  as  follows  : — 

The  gas  from  a  common  burner  is  led  by  means  of  a  vulcanized  tube  into 
two  successive  small  wash  bottles,  containing  the  alkaline  solution;  from  the 
last  of  these  it  is  led  into  a  large  Woulff 's  bottle  filled  with  water.  The 
bottle  has  two  necks,  and  a  tap  at  the  bottom ;  one  of  the  necks  contains 
the  cork  through  which  the  tube  carrying  the  gas  is  passed;  the  other, 
a  cork  through  which  a  good-sized  funnel  with  a  tube  reaching  to  the  bottom 
of  the  bottle  is  passed.  When  the  gas  begins  to  bubble  through  the  flask, 
the  tap  is  opened  so  as  to  allow  the  water  to  drop  rapidly ;  if  the  pressure  of 
gas  is  strong,  the  funnel  tube  acts  as  a  safety  valve,  and  allows  the  water  to 
rise  up  into  the  cup  of  the  funnel.  When  a  sufficient  quantity  of  gas  has 
passed  into  the  bottle,  say  six  or  eight  pints,  the  water  which  has  issued  from 
the  tap  into  some  convenient  vessel  is  measured  into  cubic  inches  or  liters, 
and  gives  the  quantity  of  gas  which  has  displaced  it.  In  order  to  insure 
accurate  measurement,  all  parts  of  the  apparatus  must  be  tight. 

The  flasks  are  then  separated,  and  into  the  second  5  c.c.  of  arsenious 
solution  placed,  and  acidified  slightly  with  HC1.  If  any  traces  of  a 
precipitate  occur  it  is  set  aside  for  titration  with  the  contents  of  the  first 
flask/into  which  10  c.c.  or  so  of  arsenious  solution  are  put,  acidified  as 
before,  both  mixed  together,  diluted  to  a  given  measure,  filtered,  and  a 
measured  quantity  titrated  as  before  described. 

This  method  does  not  answer  for  very  crude  gas  containing  large 
quantities  of  H2S  unless  the  absorbing  surface  is  largely  increased. 


2.     By   Permanganate    (Mohr). 

If  a  solution  of  H2S  is  added  to  a  dilute  solution  of  ferric 
sulphate,  the  ferric  salt  is  reduced  to  the  ferrous  state,  and  free 
sulphur  separates.  The  ferrous  salt  so  produced  may  be  measured 
accurately  by  permanganate  without  removing  the  separated 
sulphur.  Ferric  sulphate,  free  from  ferrous  compounds,  in 
sulphuric  acid  solution,  is  placed  in  a  stoppered  flask,  and  the 
solution  of  H2S  added  to  it  with  a  pipette ;  the  mixture  is  allowed 
to  stand  half  an  hour  or  so,  then  diluted  considerably,  and  per- 
manganate added  until  the  rose  colour  appears. 

56Fe  =  17  H2S 

or  each  c.c.  of  T^-  permanganate  represents  0*0017  gm.  of  H2S. 
The  process  is  considerably  hastened  by  placing  the  stoppered  flask 
containing  the  acid  ferric  liquid  into  hot  water  previous  to  the 
addition  of  H2S,  and  excluding  air  as  much  as  possible. 


316  VOLUMETRIC  ANALYSIS.  §    75. 

3.     By  Iodine. 

Sulphuretted  hydrogen  in  mineral  waters  may  be  accurately 
estimated  by  iodine  in  the  following  manner  : — 

10  c.c.  or  any  other  necessary  volume  of  Y^  iodine  solution  are  measured 
into  a  500  c.c.  flask,  and  the  water  to  be  examined  added  until  the  colour 
disappears.  5  c.c.  of  starch  liquor  are  then  added,  and  T^  iodine  until  the 
blue  colour  appears ;  the  flask  is  then  filled  to  the  mark  with  pure  distilled 
water.  The  respective  volumes  of  iodine  and  starch  solution,  together  with 
the  added  water,  deducted  from  the  500  c.c.,  will  show  the  volume  of  water 
actually  titrated  by  the  iodine.  A  correction  should  be  made  for  the  excess 
of  iodine  necessary  to  produce  the  blue  colour. 

Fresenius  examined  the  sulphur  water  of  the  Grindbrimnen, 
in  Frankfurt  a.  M.  (Z.  a.  C.  xiv.  321),  both  volumetrically  and 
by  weight  for  IPS  with  very  concordant  results.  361*44  gm.  of 
water  (correction  for  blue  colour  being  allowed)  required  20*14  c.c. 
of  iodine,  20*52  c.c.  of  which  contained  0*02527  of  free  iodine 
=  H2S  0*009194  gin.  per  million.  444*65  gin.  of  the  same  water 
required,  under  the  same  conditions,  25*05  c.c.  of  the  same  iodine 
solution  =  IPS  0*009244  gm.  per  million.  By  weight  the  IPS 
was  found  to  be  0*009377  gm.  per  million. 


TANNIC    ACID. 

§  75.  THE  estimation  of  tannin  in  the  materials  used  for 
tanning  is  by  no  means  of  the  most  satisfactory  character.  Many 
methods  have  been  proposed,  and  given  up  as  practically  useless. 
In  the  previous  editions  of  this  book  Lowenthal's  method 
(originated  by  Est court)  as  then  perfected  was  given;  but  it  is 
still  somewhat  deficient  in  accuracy  or  constancy  of  results,  although 
much  ingenuity  and  intelligence  have  been  expended  on  it. 

One  difficulty  is  still  unsurmoimted,  and  that  is,  the  preparation 
of  a  pure  tannic  acid  to  serve  as  standard.  The  various  tannins  in 
existence  are  still  very  imperfectly  understood,*  but  so  far  as  the 
comparative  analysis  of  tanning  materials  among  themselves  is 
concerned,  the  method  in  question  is  theoretically  the  best. 

The  principle  of  the  method  depends  on  the  oxidation  of  the 
tannic  acid,  together  with  other  glucosides  and  easily  oxidizable 
substances,  by  permanganate,  regulated  by  the  presence  of  soluble 
indigo-carmine,  which  also  acts  as  an  indicator  to  the  end  of  the 
reaction.  The  total  amount  of  such  substances  being  found  and 

*Von  Schroder,  whose  suggestions  have  been  adopted  by  the  German  Association 
of  Tanners,  selects  a  commercial  pure  tannic  acid  for  use  as  a  standard  by  dissolving 
2  gm.  in  a  liter  of  water.  10  c.c.  of  this  is  titrated  with  permanganate  as  described. 
50  c.c.  are  then  digested  twenty  hours  with  3  gm.  moistened  hide  powder.  10  c.c.  of 
the  filtrate  from  this  is  then  titrated,  and  if  the  permanganate  consumed  amounts  to 
less  than  10  per  c^nt.  of  the  total  consumed  by  the  tannin,  it  is  suitable  for  a  standard. 
1000  parts  being  considered  equivalent  in  reducing  power  to  1048  parts  of  tannin 
precipitable  by  hide,  according  to  Hammer's  experiments,  therefore  Von  Schroder, 
aiter  titrating  as  described,  calculates  the  dry  matter,  and  multiplies  by  the  round 
number  1'05  to  obtain  the  value  in  actual  tannin  precipitable  by  hide. 


§    75.  TANNIC   ACID.  SI 7 

expressed  by  a  known  volume  of  permanganate,  the  actual  available 
tannin  is  then  removed  by  gelatine,  and  the  second  titration  is 
made  upon  the  solution  so  obtained  in  order  to  find  the  amount  of 
oxidizable  matters  other  than  tannin. 

The  volume  of  permanganate  so  used,  deducted  from  the  volume 
used  originally,  shows  the  amount  of  tannin  actually  available  for 
tanning  purposes  expressed  in  terms  of  permanganate. 

It  will  be  at  once  seen  that  this  method  is  essentially  a  practical 
one,  because  it  is  only  the  particular  tannin  capable  of  combining 
with  organic  tissue  which  is  estimated.  It  has  been  critically 
examined  with  approbation  by  good  authorities,  among  whom  may 
be  mentioned,  Procter  (C.  N.  xxxvi.  59 ;  ibid,  xxxvii.  256), 
Kathreiner  (Z.  a.  C.  xviii.  112),  (Dingler's  Polyt.  Jour. 
cxxvii.  481),  and  Hewitt  (Tanner's  Jour.,  May,  1877,  93).  My 
own  experiments  have  shown  that  for  all  materials  containing  tannin, 
even  catechu,  it  is  the  best  process  yet  discovered,  but  requires 
patient  practice  to  ensure  concordant  results.  Lowenthal's 
description  of  the  method  is  given  in  Z.  a.  C.  xvi.  33. 

The  extraction  of  the  tannic  acid  from  the  raw  material  is  best 
performed  by  boiling  it  in  a  large  flask  with  about  a  liter  of 
distilled  water  for  half  an  hour,  then  straining,  and  diluting  when 
cold  to  1  liter.  Portions  are  filtered  if  necessary.  Concentrated 
extracts  are  dissolved  before  titration  by  adding  them  to  boiling 
water,  then  cooling  and  diluting  to  the  measure.  In  the  case  of 
strong  materials  such  as  sumach  or  valonia  10  gm.,  or  oak-bark 
20  gm.,  are  used. 

The  quantity  of  these  extracts  to  be  used  for  titration  must  be 
regulated  to  some  extent  by  the  amount  of  permanganate  required 
to  oxidize  the  tannic  and  gallic  acids  present.  Practice  and 
experience  will  enable  the  operator  to  judge  of  the  proper  propor- 
tions to  use  in  dealing  with  the  various  materials,  bearing  in  mind 
that  volumetric  processes  are  largely  dependent  upon  identity  of 
conditions  for  securing  concordant  results. 

Procter,  who  is  probably  one  of  the  best  authorities  on  this 
subject,  has  modified  to  some  extent  the  details  of  this  process 
(/.  S.  C.  I.  iii.  82,  and  ibid.  v.  79),  and  these  modifications  are 
embodied  here. 


Standard   Solutions   and  Re-agents, 

Standard  Potassic  permanganate. — Kathreiner  recommends 
that  this  solution  should  contain  not  more  than  1*333  gm.  of 
the  pure  salt  per  liter  (better  only  about  1  gm.) ;  therefore,  if 
the  operator  is  accustomed  to  use  the  decinormal  solution,  a  very 
convenient  strength  is  made  by  diluting  one  volume  of  it  with 
two  of  water,  thus  obtaining  a  solution  of  -^  strength  ( =  1  '052  gm. 
per  liter). 

This   standard  is  the  more   advisable   because   it   enables  the 


318  VOLUMETRIC  ANALYSIS.  §    75. 

operator  to  calculate  its  value  into  oxalic  acid,  and  so  arrive  at  the 
theoretical  standards  adopted  by  Neubauer  and  Oser;  namely, 
that  0*063  gm.  of  oxalic  acid  represents  0*04157  gm.  of  gallo-tannic 
acid  (gall-nut  tannin),  or  0*062355  gm.  of  querci-tannic  acid  (oak 
bark  tannin).  These  coefficients  for  calculation  are  now  largely 
adopted,  and  are  certainly  preferable  to  standardizing  the  perman- 
ganate upon  any  specimen  of  so-called  pure  tannin. 

30  c.c.  of  ^  permanganate  will  therefore  represent  0*063  gm. 
of  oxalic  acid  or  the  weights  of  tannin  above  mentioned. 

Solution  of  Indigo  Carmine. — This  should  be  a  clear  solution  of 
about  5  gin.  to  the  liter  with  about  50  c.c.  of  pure  H2S04. 

Solution  of  Gelatine. — This  solution  is  used  to  precipitate  the 
available  tannin  in  any  given  solution  after  its  total  oxidizable 
matters  have  been  determined  by  the  indigo  and  permanganate.  It 
should  be  made  fresh  for  each  series  of  titrations,  by  dissolving 
2  gm.  of  kelson's  gelatine  in  100  c.c.  of  water  and  filtering. 

Dilute  Sulphuric  Acid.— 1*10. 

Processes  of  Titration:  The  first  thing  to  be  done  is  to  ascertain  the 
relationship  between  the  permanganate  and  indigo  solutions  (it  is  assumed 
that  the  permanganate  is  correct  as  regards  its  relation  to  oxalic  acid),  and 
therefore  10  or  20  c.c.  of  the  indigo  are  measured  into  a  white  porcelain  basin, 
and  diluted  to  f  of  a  liter  with  distilled  water,  or  good  ordinary  water  free 
from  organic  matter  or  other  substances  capable  of  reducing  permanganate. 
10  c.c.  of  the  dilute  acid  are  measured  in,  and  the  permanganate  delivered 
in  with  a  hand-pipette  in  drops,  with  constant  stirring,  until  the  colour  is 
just  discharged,  leaving  a  clear  faint  yellow  tint,  with  just  a  shade  of  pink  at 
the  rim. 

This  experiment  will  act  as  a  guide  to  the  final  adjustment  of  the  indigo 
with  an  accurate  30  c.c.  burette  in  TV,  which  should  be  of  such  dilution  that 
about  20  c.c.  correspond  to  about  15  c.c.  of  permanganate. 

Titration  of  the  Tanning  Material :  It  is  very  important,  in  order  to 
avoid  uncertainty  in  the  end-point  of  the  reaction,  that  only  so  much 
material  shall  be  used  as  shall  consume  about  7  or  8  c.c.  of  permanganate  of 
-j^j-  strength  above  that  point  which  is  required  for  the  indigo. 

Procter  and  Kathreiner  both  insist  upon  these  proportions,  and  the 
general  method  adopted  by  them  is  to  add  20  c.c.  of  indigo  with  10  c.c.  of 
dilute  acid  to  about  •£  of  a  liter  of  water,  in  a  porcelain  dish,  followed  by  5  c.c. 
of  tannin  solution.  The  permanganate  is  then  delivered  in  very  slowly,  with 
constant  stirring,  until  a  faint  rose  colour  appears  round  the  edges  of  the 
liquid.  The  time  allowed  for  the  titration  is  also  very  important. 

Von  Schroder,  representing  the  Association  of  German  Tanners, 
prefers  to  add  the  permanganate  1  c.c.  at  a  time  with  vigorous 
stirring,  until  the  colour  of  the  liquid  indicates  that  a  few  drops 
only  are  required  to  end  the  titration.  Procter,  on  the  other 
hand,  prefers  the  rapid  drop  method  for  the  commencement,  and 
until  near  the  end.  He  also  finds  that  the  method  of  stirring 
influences  the  result  in  no  very  slight  degree.  Whatever  plan  the 


§    75.  TANNIC  ACID.  319 

operator  adopts,  it  is  advisable  to  keep  consistently  to  it  in  order 
that  the  results  may  be  comparatively  the  same. 

It  must  be  remembered  that  neither  by  this  nor  any  other  method 
is  it  possible  to  accurately  estimate  the  tannin,  but  only  as  a  means 
of  comparing  two  samples  of  the  same  material. 

Precipitation  of  the  Tannin,  and  subsequent  Titration  of  Substances 
other  than  Tannin. — Procter's  procedure  is  to  take  50  c.c.  of  the  tannin 
infusion  (5  c.c.  of  which  has  been  titrated),  and  add  to  it  28'6  c.c.  of  gelatine 
solution  in  a  flask  holding  about  150  c.c.  The  mixture  is  well  shaken,  then 
saturated  with  clean  table  salt,  and  10  c.c.  of  the  dilute  acid  added,  together 
with  a  teaspoonful  of  kaolin :  the  whole  is  vigorously  shaken,  then  filtered, 
and  made  up  to  exactly  100  c.c.  10  c.c.  of  this  liquid,  representing  5  c.c.  of 
the  tannin  decoction,  is  then  titrated  in  precisely  the  same  manner  as  before. 
The  calculation  of  percentage  is  then  made  as  follows :  Let  the  first  titration 
(two  of  which  should  be  made  for  security)  be  called  a ;  the  second,  also  in 
duplicate,  I.  If  further,  c  be  the  quantity  of  permanganate  required  to 
oxidize  10  c.c.  of  ^  oxalic  acid,  and  10  gm.  of  substance  have  been  employed 
for  1  liter  of  decoction,  then  c  :  (a — b)  :  :  6*3  :  x,  where  x  is  the  percentage 
of  tannin  expressed  in  terms  of  oxalic  acid. 

Hunt,  who  is  also  an  undoubted  authority  on  tannin  estimation, 
differs  from  Procter  on  the  question  of  saturating  the  liquid  for 
final  titration  with  salt  (/.  C.  S.  I.  iv.  263),  011  the  ground  that,  in 
the  case  of  material  containing  much  gallic  acid,  some  of  it  is 
precipitated  with  the  tannin,  thus  leading  to  higher  results.  This 
he  has  proved  by  experiment,  and  therefore  prefers  to  act  as 
follows : — 

50  c.c.  of  the  tannin  solution  are  run  into  a  small  dry  flask,  to  this  25  c.c. 
of  the  fresh  filtered  gelatine  solution  are  added,  and  the  flask  shaken.  25  c.c. 
of  a  saturated  solution  of  salt,  containing  50  c.c.  of  strong  H2SO4  per  liter 
are  now  added,  and  about  a  teaspoonful  of  kaolin  or  baric  sulphate.  The 
flask  is  thoroughly  shaken  for  a  few  minutes,  after  which  a  clear  bright 
filtrate  may  be  obtained. 

For  materials  containing  over  45  per  cent,  tannin,  it  is  advisable 
to  take  25  c.c.  instead  of  50,  and  to  use  50  c.c.  of  salt,  the  amount 
of  gelatine  solution  being  the  same.  The  same  authority  also  states 
that,  for  gambier  and  its  allies,  the  method  of  titration  as  above 
described  does  not  give  accurate  results,  inasmuch  as  the  gelatine 
and  salt  do  not  remove  all  the  substances  of  tanning  value  from  the 
liquid.  In  such  case  it  is  necessary  to  digest  the  liquid  for  at  least 
twelve  hours  with  pure  dry  skin  shavings  in  powder.  The  mixture 
is  then  filtered  and  titrated  in  the  usual  way. 

It  is  impossible  to  give  here  the  opinions  held  by  various 
authorities  on  this  subject,  therefore  the  reader  who  desires  fuller 
information  should  consult  the  papers  to  which  reference  has  been 
made. 

The  following  table  given  by  Hunt  is  however  appended,  as  the 
result  of  careful  working,  and  as  a  guide  to  the  nature  of  various 
tanning  materials : — 

The  "  total  extract "  in  the  table  was  determined  by  evaporating 


320 


VOLUMETRIC   ANALYSIS. 


§  75. 


a  portion  of  the  tannin  solution  to  clryiiess  in  a  small  porcelain 
basin  and  drying  the  residue  at  110°  C.  The  "insoluble  matter" 
was  also  dried  at  110°  C. 


NAME  OF  MATERIAL. 

Total 
matters 
oxidized 
by  Perman- 
ganate, as 
Oxalic  Ac. 

Tannin,  as 
Oxalic  Ac. 
(Procter) 

Tannin,  as 
Oxalic  Ac. 
(Hunt) 

Total 
Extract. 

Insoluble. 

per  cent. 

per  cent. 

per  cent. 

per  cent. 

per  cent. 

English  Oak  Bark    .  .  . 

15-70 

13-54 

11-97 

18-38 

66-15 

CanadiauHemlock  Bark 

9-03 

7-46 

7-08 

13-96 

75-25 

Larch  Bark               .  . 

8'20 

7"17 

6'15 

20'64 

60"  80 

Mangrove  Bark 

31-35 

2971 

28-48 

26-60 

49-70 

Alder  Bark       

8-27 

6-15 

5-73 

19-36 

68-00 

Blue  Gum  Bark 

10-18 

8-91 

8-91 

11-76 

74-65 

Valonia      

37-41 

35-24 

30-50 

38-50 

46-05 

Myrabolans       

48-23 

38-43 

38-00 

42-80 

— 

Sumach      

42-53 

34-30 

31-46 

44-10 

47-77 

Betel  Nut  

15.91 

13-87 

13-79 

17-94 

67-00 

Turkish  Blue  Galls  ... 

73-38 

65-83 

59-96 

48*40 

36-35 

Aleppo  Galls     

98-85 

87-82 

83-05 

68-80 

14-32 

Wild  Galls 

26"21 

18'75 

16'56 

31-70 

54'17 

Divi-Divi  

66-98 

62-62 

61-22 

54-38 

29-90 

Balsamocarpon    (poor 

and  old  sample)     .  .  . 

50-49 

37-76 

32-88 

57-14 

28-25 

Pomegranate  Kind  .  .  . 

27-58 

24-18 

23-12 

41*00 

49-50 

Tormentil  Root 

22-27 

20-98 

20-68 

19-70 

67-95 

Rhatany  Eoot  

22-27 

20-15 

19-30 

18-80 

66-00 

Pure  Indian  Tea 

23-06 

18*65 

17-40 

34-46 

53-40 

Pure  China  Tea 

18-03 

1421 

14-09 

24-50 

62-60 

Cutch  

57-65 

51-95 

44-24 

61-60 

4'75 

Gum  Kino         

66-39 

59-55 

51-55 

79-30 

i-oo 

Hemlock  Extract 

35-16 

33-17 

30-98 

48-78 

— 

Oak  wood  Extract     .  .  . 

33'49 

26-90 

23-86 

37-78 

— 

Chestnut  Extract     .  .  . 

39-77 

32-63 

28-88 

50-28 

— 

Quebracho  Extract  ... 

48-22 

44-45 

40-84 

49-00 

— 

"  Pure  Tannin  " 

135-76 

122-44 

121-93 

— 

— 

Tan  Liquor,  sp.  gr.  1/030 
Spent  Tan  Liquor,  sp. 

4-84 

3-14 

2-10 

6-01 

— 

gr.  T0165      

1-40 

0-37 

0'25 

3-10 

— 

Absorbed 

by  Dry 

Pure  Skin. 

Gambier,  Cube  

70-12 

— 

51-07 

74-40 

5-31 

„        Sarawak   ... 

63-13 

— 

47-09 

70-70 

3-67 

Bale  

56-00 

— 

43-70 

63-54 

1-40 

Other    Methods    of   Estimating-    Tannin. 

Direct  Precipitation  by  Gelatine. — The  difficulty  existing  with 
this  method  is  that  of  getting  the  precipitate  to  settle,  so  that  it 
may  be  clearly  seen  when  enough  gelatine  has  been  added. 

Tolerably  good  results  may  sometimes  be  obtained  by  using  a 


§  76.  TIN.  321 

strong  solution  of  sal  ammoniac  or  chrome  alum  as  an  adjunct. 
The  best  aid  is  probably  barium  sulphate,  2  or  3  gm.  of  which 
should  be  added  to  each  portion  of  liquid  used  for  titration. 

The  Standard  Solution  of  Gelatine  should  contain  1'33  gm.  of 
dry  gelatine  per  liter,  in  which  is  also  mixed  100  c.c.  of  cherry 
laurel  water  to  preserve  it.  45  c.c.  =  0*05  gm.  tannin  (Carles). 
This  method  is  adapted  only  for  rough  technical  purposes,  as  also 
the  following. 

Direct  Precipitation  by  Antimony. — This  method  is  still  in 
favour  with  some  operators ;  but,  like  the  gelatine  process,  is  beset 
with  the  difficulty  of  getting  the  precipitate  to  settle. 

The  Standard  Antimony  Solution  is  made  by  dissolving  2*611 
gm.  of  crystals  of  emetic  tartar  dried  at  100°  C.  in  a  liter.  1  c.c.  = 
0*005  gm.  tannin.  50  c.c.  of  the  tannin  solution  may  be  taken 
for  titration,  to  which  is  added  1  or  2  gm.  of  sal  ammoniac,  and  the 
antimonial  solution  run  in  until  no  further  cloudiness  is  produced. 

In  both  the  above  methods  the  final  tests  must  either  be  made 
by  repeatedly  filtering  small  portions  to  ascertain  whether  the 
precipitation  is  complete,  or  by  bringing  drops  of  each  liquid 
together  on  black  glass  or  a  small  mirror. 


TIN. 

Sn=118. 

Metallic  iron  x          1*0536  =  Tin. 

Double  iron  salt          x          0*1505=    ,, 
Factor  for  —^  iodine 

or    permanganate 

solution  0*0059 

§  76.  THE  method,  originally  devised  by  Streng,  for  the 
direct  estimation  of  tin  by  potassic  bichromate,  or  other  oxidizing 
agents  in  acid  solution,  has  been  found  most  unsatisfactory,  from 
the  fact  that  variable  quantities  of  water  or  acid  seriously  interfere 
with  the  accuracy  of  the  results.  The  cause  is  not  fully  under- 
stood, but  that  it  is  owing  partly  to  the  oxygen  mechanically 
contained  in  the  water  reacting  on  the  very  sensitive  stannous 
chloride  there  can  be  very  little  doubt,  as  the  variations  are 
considerably  lessened  by  the  use  of  water  recently  boiled  and 
cooled  in  closed  vessels.  These  difficulties  are  set  aside  by  the 
processes  of  Lenssen,  Lbwenthal,  Stromeyer,  and  others,  now 
to  be  described,  and  which  are  found  fairly  satisfactory. 

1.    Direct    Titration    by    Iodine    in    Alkaline    Solution    (Lenssen). 

Metallic  tin  or  its  protosalt,  if  not  already  in  solution,  is 
dissolved  in  hydrochloric  acid,  and  a  tolerable  quantity  of  Kochelle 


322  VOLUMETRIC   ANALYSIS.  §    76. 

salt  added,  together  with  sodic  bicarbonate  in  excess.  If 
enough  tartrate  be  present,  the  solution  will  be  clear;  starch  is 
then  added,  and  the  mixture  titrated  with  ~  iodine.  Metallic  tin 
is  best  dissolved  in  HC1  by  placing  a  platinum  crucible  or  cover  in 
contact  with  it,  so  as  to  form  a  galvanic  circuit. 

Benas  (Ghem.  Centr-blatt.  li.  957)  points  out  that  the  chief 
error  in  the  estimation  as  above  arises  from  oxygen  dissolved  in. 
the  liquid,  or  absorbed  during  the  operation.  In  order  to  obtain 
constant  results,  it  is  necessary  to  dissolve  the  tin  compound 
in  HC1,  dilute  with  oxygen-free  water,  and  add  at  once  excess  of 
standard  iodine,  which  excess  is  found  by  residual  titration  with 
standard  thiosulphate. 

2.     Indirect    Titration    by    Ferric    Chloride    and    Permanganate 
(Lowenthal,    Stromeyer,    etc.). 

This  method  owes  its  value  to  the  fact,  that  when  stannous 
chloride  is  brought  into  contact  with  ferric  or  cupric  chloride,  it 
acts  as  a  reducing  agent,  in  the  most  exact  manner,  upon  these 
compounds,  stannic  chloride  being  formed,  together  with  a  pro- 
portionate quantity  of  ferrous  or  cuprous  salt,  as  the  case  may  be. 
If  either  of  the  latter  be  then  titrated  with  permanganate,  the 
original  quantity  of  tin  may  be  found,  the  reaction  being,  in  the 
case  of  iron, — 

SnCl2  +  Fe2Cl6  =  SnCl4  +  2FeCl2. 

56  iron  =  59  tin.  If  decinormal  permanganate,  or  the  factor 
necessary  to  convert  it  to  that  strength,  be  used,  the  calculation  by 
means  of  iron  is  not  necessary. 

The  Analysis :  The  solution  of  stannous  chloride,  or  other  protosalt  of  tin 
in  HC1,  or  the  granulated  metal,  is  mixed  with  pure  ferric  chloride,  which, 
if  tolerably  concentrated,  dissolves  metallic  tin  readily,  and  without  evolution 
of  hydrogen,  then  diluted  with  distilled  water,  and  titrated  with  perman- 
ganate as  usual.  To  obtain  the  most  exact  results,  it  is  necessary  to  make  an 
experiment  with  the  same  permanganate  upon  a  like  quantity  of  water, 
to  which  ferric  chloride  is  added;  the  quantity  required  to  produce  the 
same  rose  colour  is  deducted  from  the  total  permanganate,  and  the  remainder 
calculated  as  tin. 

Stannic  salts,  also  tin  compounds  containing  iron,  are  dissolved  in  water, 
HC1  added,  and  a  plate  of  clean  zinc  introduced  for  ten  or  twelve  hours ; 
the  tin  so  precipitated  is  carefully  collected  and  washed,  then  dissolved 
in  HC1,  and  titrated  as  above ;  or  the  finely  divided  metal  may  at  once 
be  mixed  with  an  excess  of  ferric  chloride,  a  little  HC1  added,  and  when 
solution  is  complete,  titrated  with  permanganate.  4  eq.  of  iron  (=224) 
occurring  in  the  form  of  ferrous  chloride  represent  1  eq.  (=118)  of  tin. 

Tin  may  also  be  precipitated  from  slightly  acid  peroxide  solution 
as  sulphide  by  H2S,  the  sulphide  well  washed,  and  mixed  with 
ferric  chloride,  the  mixture  gently  warmed,  the  sulphur  filtered  off, 
and  the  filtrate  then  titrated  with  permanganate  as  above.  4  eq. 
of  iron  =  1  eq.  of  tin. 


§  77.  ZINC.  323 

Tin  Ore. — In  the  case  of  analysis  of  cassiterite,  Arnold  (C.  N. 
xxxvi.  238)  recommends  that  1  gm.  of  the  very  finely  powdered 
mineral  be  heated  to  low  redness  for  two  hours  in  a  porcelain  boat 
in  a  glass  tube  with  a  brisk  current  of  dry  and  pure  hydrogen  gas, 
by  which  means  the  metal  is  reduced  to  the  metallic  state.  It  is 
then  dissolved  in  acid  ferric  chloride,  and  titrated  with  perman- 
ganate or  bichromate  in  the  usual  way. 


URANIUM. 
Ur  =  240. 

§  77.  THE  estimation  of  uranium  may  be  conducted  with  great 
accuracy  by  permanganate,  in  precisely  the  same  way  as  ferrous 
salts  (§  59).  The  metal  must  be  in  solution  either  as  acetate, 
sulphate,  or  chloride,  but  not  nitrate.  In  the  latter  case  it  is 
necessary  to  evaporate  to  dryness  with  excess  of  sulphuric  or 
hydrochloric  acid,  or  to  precipitate  with  alkali,  wash  and  redissolve 
in  acetic  acid. 

The  reduction  to  the  uranous  state  is  made  with  zinc,  but  as  the 
end  of  reduction  cannot,  like  iron,  be  known  by  the  colour,  it  is 
necessary  to  continue  the  action  for  a  certain  time ;  in  the  case  of 
small  quantities  a  quarter,  larger  half  an  hour,  at  a  temperature  of 
50°  to  60°  C.,  and  in  the  presence  of  excess  of  sulphuric  acid ; 
all  the  zinc  must  be  dissolved  before  titration.  The  solution  is 
then  freely  diluted  with  boiled  water,  sulphuric  acid  added  if 
necessary,  and  then  permanganate  until  the  rose  colour  is  faintly 
permanent.  The  ending  is  distinct  if  the  solution  be  well  diluted, 
and  the  reaction  is  precisely  the  same  as  in  the  case  of  ferrous 
salts ;  namely,  2  eq.  of  uranium  existing  in  the  uranous  state 
require  1  eq.  of  oxygen  to  convert  them  to  the  uranic  state ;  hence 
56  Fe  =  120  Ur,  consequently  the  strength  of  any  permanganate 
solution  in  relation  to  iron  being  known,  it  is  easy  to  find  the 
amount  of  uranium. 

ZINC. 
Zn=65. 

1  c.c.  •£$  solution  =  0-00325  gm.  Zinc. 

Metallic  iron         x  0-5809      =  Zinc. 

x  0-724        =  Zinc  oxide. 

Double  iron  salt  x  0*08298    =  Zinc. 

„  „  x  0-1034       =  Zinc  oxide. 

1.      Indirect    Method    (Mann). 

§  78.  THIS  process  gives  exceedingly  good  results,  and  consists 
in  precipitating  the  zinc  as  hydrated  sulphide,  decomposing  the 

Y  2 


324  VOLUMETKIC   ANALYSIS.  §    78. 

sulphide  with  moist  silver  chloride,  then  estimating  the  zinc 
chloride  so  formed  with  animonic  sulphocyanate  as  in  Volhard's 
method  (§  39). 

The  requisite  materials  are — 

Silver  chloride. — Well  washed  and  preserved  from  the  light 
under  water. 

Standard  Silver  nitrate. — 33'18  gm.  of  pure  silver,  dissolved  in 
nitric  acid  and  made  up  to  1  liter,  or  52*3  gm.  silver  nitrate  per 
liter.  If  made  direct  from  silver,  the  solution  must  be  well  boiled 
to  dissipate  nitrous  acid.  1  c.c.  =0'01  gm.  of*  zinc. 

Ammonic  sulphocyanate. — Of  such  strength  that  exactly  3  c.c. 
suffice  to  precipitate  1  c.c.  of  the  silver  solution. 

Ferric  Indicator  and  Pure  Xitric  Acid  (see  §  39.3  and  4). 

The  Analysis :  0'5  to  1  gm.  of  the  zinc  ore  is  dissolved  in  nitric  acid. 
Heavy  metals  are  removed  by  H2S,  iron  and  alumina  by  double  precipitation 
with  ammonia.  The  united  filtrates  are  acidified  with  acetic  acid,  and  H2S 
passed  into  the  liquid  until  all  zinc  is  precipitated  as  sulphide.  Excess  of 
H2S  is  removed  by  rapid  boiling,  so  that  a  drop  or  two  of  the  filtered  liquid 
gives  no  further  stain  on  lead  paper.  The  precipitate  is  then  allowed  to  settle, 
decanted  while  hot,  the  precipitate  brought  on  a  filter  with  a  little  hot  water, 
and  without  further  washing,  the  filter  with  its  contents  is  transferred  to 
a  small  beaker,  30 — 50  c.c.  of  hot  water  added,  well  stirred,  and  so  much 
moist  silver  chloride  added  as  i?  judged  necessary  to  decompose  the  sulphide, 
leaving  an  excess  of  silver.  The  mixture  is  now  boiled  till  it  shows  signs  of 
settling  clear  ;  5  or  6  drops  of  dilute  sulphuric  acid  (1:5)  are  added  to  the 
hot  mixture,  and  in  a  few  minutes  the  whole  of  the  zinc  sulphide  will  be 
converted  into  zinc  chloride.  The  free  sulphur  and  excess  of  silver  chloride 
are  now  filtered  off,  washed,  and  the  chloride  in  the  mixed  filtrate  and 
washings  estimated  as  follows  : — 

To  the  cool  liquid,  measuring  200  or  300  c.c.,  are  added  5  c.c.  of  ferric 
indicator,  and  so  much  pure  nitric  acid  as  is  necessary  to  remove  the  yellow 
colour  of  the  iron.  A  measured  excess  of  the  standard  silver  solution  is  then 
delivered  in  with  the  pipette,  and  without  filtering  off  the  silver  chloride, 
or  much  agitation,  so  as  to  clot  the  precipitate,  the  sulphocyanate  is  cautiously 
added,  with  a  gentle  movement  after  each  addition,  until  a  permanent  light 
brown  colour  appears. 

The  volume  of  silver  solution  represented  by  the  sulphocyanate 
being  deducted  from  that  originally  used,  will  give  the  volume  to 
be  calculated  to  zinc,  each  c.c.  being  equal  to  O'Ol  gm.  Zn. 


2.    Precipitation  as  Sulphide  and  subsequent  titration  with  Ferric 
Salts  and  Permanganate  (Schwarz). 

The  principle  of  this  method  is  based  on  the  fact,  that  when  zinc 
sulphide  is  mixed  with  ferric  chloride  and  hydrochloric  acid,  or 
better  still,  with  ferric  sulphate  and  sulphuric  acid,  ferrous  or  zinc 
chloride,  or  sulphates  respectively,  and  free  sulphur  are  produced. 
If  the  ferrous  salt  so  produced  is  estimated  with  permanganate  or 


§  78.  ZINC.  325 

bichromate,  the  proportional  quantity  of  zinc  present  is  ascertained. 
2  eq.  Fe  represent  1  eq.  Zn. 

Preparation  of  the  Ammoniacal  Zinc  Solution. — In  the  case  of  rich 
ores  1  gm.,  and  poorer  qualities  2  gm.,  of  the  finely  powdered  material  are 
placed  into  a  small  wide-mouthed  flask,  and  treated  with  HC1,  to  which 
a  little  nitric  acid  is  added,  the  mixture  is  warmed  to  promote  solution,  and 
when  this  has  occurred  the  excess  of  acid  is  evaporated  by  continued  heat. 
If  lead  is  present,  a  few  drops  of  concentrated  sulphuric  acid  are  added 
previous  to  complete  dryness,  in  order  to  render  the  lead  insoluble;  the 
residue  is  then  extracted  with  water  and  filtered.  Should  metals  of  the  fifth 
or  sixth  group  be  present,  they  must  be  removed  by  H2S  previous  to  the 
following  treatment.  The  solution  will  contain  iron,  and  in  some  cases 
manganese.  If  the  iron  is  not  already  fully  oxidized,  the  solution  must  be 
boiled  with  nitric  acid ;  if  only  traces  of  manganese  are  present,  a  few  drops 
of  bromized  HC1  should  be  added.  When  cold,  the  solution  may  be  further 
diluted  if  necessary,  and  then  super-saturated  with  ammonia  to  precipitate 
the  iron  ;  if  the  proportion  of  this  metal  is  small,  it  will  suffice  to  filter  off 
and  wash  the  oxide  with  ammoniacal  warm  water,  till  the  washings  give  no 
precipitate  of  zinc  on  adding  ammonic  sulphide.  Owing  to  the  fact  that 
this  iron  precipitate  tenaciously  holds  about  a  fifth  of  its  weight  of  zinc,  it 
will  be  necessary  when  the  proportion  is  large  to  redissolve  the  partly  washed 
precipitate  in  HC1,  and  reprecipitate  (best  as  basic  acetate) ;  the  filtrate  from 
this  second  precipitate  is  added  to  the  original  zinc  filtrate,  and  the  whole 
made  up  to  a  liter. 

The  Analysis :  The  ammoniacal  zinc  solution  (prepared  as  described  above) 
is  heated,  and  the  zinc  precipitated  in  a  tall  beaker,  with  a  slight  excess  of 
sodic  or  ammonic  sulphide,  then  covered  closely  with  a  glass  plate,  and  set 
aside  in  a  warm  place  for  a  few  hours.  The  clear  liquid  is  removed  by 
a  syphon,  and  hot  water  containing  some  ammonia  again  poured  over  the 
precipitate,  allowed  to  settle,  and  again  removed,  and  the  washing  by 
decantation  repeated  three  or  four  times ;  finally,  the  precipitate  is  brought 
upon  a  tolerably  large  and  porous  filter,  and  well  washed  with  warm  water 
containing  ammonia,  till  the  washings  no  longer  discolour  an  alkaline  lead 
solution.  The  filter  pump  may  be  used  here  with  great  advantage. 

The  filter  with  its  contents  is  then  pushed  through  the  funnel  into  a  large 
flask  containing  a  sufficient  quantity  of  ferric  sulphate  mixed  with  sulphuric 
acid,  immediately  well  stopped  or  corked,  gently  shaken,  and  put  into  a  warm 
place ;  after  some  time  it  should  be  again  well  shaken,  and  set  aside  quietly 
for  about  ten  minutes.  After  the  action  is  all  over  the  mixture  should  possess 
a  yellow  colour  from  the  presence  of  undecomposed  ferric  salt ;  when  the 
cork  or  stopper  is  lifted  there  should  be  no  odour  of  H2S.  The  flask  is  then 
nearly  filled  with  cold  distilled  water,  if  necessary  some  dilute  sulphuric  acid 
added,  and  the  contents  of  the  flask  titrated  with  permanganate  or  bichromate 
as  usual. 

The  free  sulphur  and  filter  will  have  no  reducing  effect  upon 
the  permanganate  if  the  solution  be  cool  and  very  dilute. 


3.    Precipitation  by  Standard  Sodic  Sulphide,  -with  Alkaline  Lead 
Solution  as  Indicator  (applicable  to  most  Zinc  Ores  and  Products). 

The  Ammoniacal  Solution  of  Zinc  is  prepared  just  as  previously 
described  in  Schwarz's  method. 

Standard  Sodic  sulphide. — A  portion  of  caustic  soda  solution  is 


326  VOLUMETRIC   ANALYSIS.  §    78. 

saturated  with  H2S,  sufficient  soda  added  to  remove  the  odour  of 
the  free  gas,  and  the  whole  diluted  to  a  convenient  strength  for 
titrating. 

Standard  Zinc  Solution. — 44'12  gm.  of  pure  zinc  sulphate  is 
dissolved  to  the  liter.  1  c.c.  will  then  contain  O'Ol  gm.  of 
metallic  zinc,  and  upon  this  solution,  or  one  prepared  from  pure 
metallic  zinc  of  the  same  strength,  the  sulphide  solution  must  be 
titrated. 

Alkaline  Lead  Indicator. — Is  made  by  heating  together  acetate 
of  lead,  tartaric  acid,  and  caustic  soda  solution  in  excess,  until 
a  clear  solution  is  produced.  It  is  preferable  to  mix  the  tartaric 
acid  and  soda  solution  first,  so  as  to  produce  sodic  tartrate ;  or  if 
the  latter  salt  is  at  hand,  it  may  be  used  instead  of  tartaric  acid. 
Some  operators  use  sodic  nitroprusside  instead  of  lead. 

The  Analysis :  50  c.c.  of  zinc  solution  (— 0'5  gm.  Zn)  are  put  into  a 
beaker,  a  mixture  of  solutions  of  ammonia  and  ammonic  carbonate  (3  of  the 
former  to  about  1  of  the  latter)  added  in  sufficient  quantity  to  redissolve 
the  precipitate  which  first  forms.  A  few  drops  of  the  lead  solution  are 
then,  by  means  of  a  glass  rod,  placed  at  some  distance  from  each  other,  on 
filtering  paper,  laid  upon  a  slab  or  plate. 

The  solution  of  sodic  sulphide  contained  in  an  ordinary  Mohr's  burette 
is  then  suffered  to  flow  into  the  zinc  solution  until,  on  bringing  a  drop  from 
the  mixture  and  placing  it  upon  the  filtering  paper,  so  that  it  may  expand 
and  run  into  the  drop  of  lead  solution,  a  black  line  occurs  at  the  point  of 
contact ;  the  reaction  is  very  delicate.  At  first  it  will  be  difficult,  probably, 
to  hit  the  exact  point,  but  a  second  trial  with  25  or  50  c.c.  of  zinc  solution 
will  enable  the  operator  to  be  certain  of  the  corresponding  strength  of  the 
sulphide  solution.  As  this  latter  is  always  undergoing  a  slight  change,  it  is 
necessary  to  titrate  occasionally. 

Direct  titration  with  pure  zinc  solution  gave  99'6  and  100'2,  instead  of  100. 

Groll  recommends  the  use  of  protochloride  of  nickel  as  indicator, 
instead  of  sodic  nitroprusside  or  lead.  The  drops  are  allowed  to 
flow  together  on  a  porcelain  plate ;  while  the  point  of  contact  shows 
a  blue  or  green  colour  the  zinc  is  not  all  precipitated  by  the  sodic 
sulphide,  therefore  the  latter  must  be  added  until  a  greyish  black 
colour  appears  at  contact. 

Another  indicator  is  paper  soaked  in  a  nearly  neutral  dilute 
solution  of  cobaltous  chloride,  which  when  dry  and  cold  is  colour- 
less. When  touched  with  a  drop  of  liquid  containing  sodic  sulphide 
it  turns  to  a  green  tint,  rapidly  becoming  brown  when  warmed. 


4.    Precipitation  as   Sulphide   -with   Ferric   Indicator   (Schaffner). 

Schaffner's  modification  of  this  process,  and  which  is  used 
constantly  at  the  laboratory  of  the  Vieille  Montagne  and  the 
Rhenish  Zinc  Works,  is  conducted  as  follows  : — For  ores  containing 
over  35  per  cent,  zinc,  0'5  gm.  is  taken ;  for  poorer  ones,  1  gm.  to 
2  gm.  Silicates,  carbonates,  or  oxides,  are  treated  with  hydro- 


§  78.  ZINC.  327 

chloric  acid,  adding  a  small  proportion  of  nitric  acid  at  boiling  heat 
to  peroxidize  the  iron.  Sulphur  ores  are  treated  with  aqua  rer/ia, 
evaporated  to  dryness,  and  the  zinc  afterwards  extracted  by  hydro- 
chloric acid;  the  final  ammoniacal  solution  is  then  prepared  as 
described  on  page  325. 

The  Analysis :  The  titration  is  made  with  a  solution  of  sodic  sulphide, 
1  c.c.  of  which  should  equal  about  O'Ol  gin.  Zn.  The  Vieille  Montague 
laboratory  uses  ferric  chloride  as  an  indicator,  according  to  Schaffner's 
method.  For  this  purpose  a  single  drop  or  some  few  drops  of  this  chloride 
are  let  fall  into  the  ammoniacal  solution  of  zinc.  The  iron  which  has  been 
added  is  at  once  converted  into  red  flakes  of  hydrated  ferric  oxide,  which 
float  at  the  bottom  of  the  flask.  If  sodic  sulphide  be  dropped  from  a  burette 
into  the  solution  of  zinc,  a  white  precipitate  of  zinc  sulphide  is  at  once 
thrown  down,  and  the  change  in  the  colour  of  the  flakes  of  iron  from  red  to 
black  shows  the  moment  when  all  the  zinc  is  sulphuretted,  and  the  titration 
is  ended.  It  is  advisable  to  keep  the  solution  for  titration  at  from  40  to 
60°  C.  Titration  carried  out  under  exactly  equal  conditions,  with  a  known 
and  carefully  weighed  proportion  of  zinc,  gives  comparative  data  for 
calculation,  and  thus  for  the  determination  of  the  contents  of  any  zinc 
solution  by  means  of  a  simple  equation.  If,  for  example,  30'45  c.c.  of  sodic 
sulphide  have  been  used  to  precipitate  0'25  gm.  of  zinc,  1  c.c.  of  it  will 
precipitate  8'21  m.gm.  of  zinc  (30'45  :  0'25=1  :  x,  and  therefore  tf=0'00821). 

Practice  has  pointed  out  the  following  concentrations  and  pro- 
portions as  best  suited  for  the  successful  execution  of  these 
titrations. 

The  sodic  sulphide  solution  which  is  used  for  titration  must  be 
such  that  1  c.c.  precipitates  8  to  10  m.gm.  of  zinc.  The  solution 
which  contains  the  zinc  which  has  to  be  estimated  will  comply 
with  the  best  conditions,  if  its  volume  varies  between  the  limits 
of  175  and  225  c.c.  It  is  advisable  that  all  solutions  of  zinc 
should  be  pretty  equally  saturated  with  ammonia,  so  that  the 
ferric  chloride  added  as  an  indicator  may  be  precipitated  in  the 
same  manner  in  all  samples,  and  so  that  the  flakes  of  iron  may  be 
always  clean  and  clear.  Freshly  prepared  ferric  chloride  gives  the 
most  delicate  results. 

The  essential  point  of  the  volumetric  process  practised  at  the 
Vieille  Montagne  is  the  perfect  uniformity  of  working  adopted  in 
the  assays  with  reference  to  the  volume  of  the  solutions  and 
reagents  used  and  the  colour  of  the  indicator.  In  titrating, 
the  same  quantities  of  ferric  chloride,  hydrochloric  acid  and 
ammonia  are  steadily  used.  Work  is  done  always  at  one  tem- 
perature and  in  the  same  time,  particularly  at  the  end  of  the 
operation,  when  the  iron  begins  to  take  on  that  characteristic 
colour  which  the  flakes  take  at  the  edges — points  which  should 
not  be  overlooked.  As  a  further  precaution,  the  titrating 
apparatus  is  provided  in  duplicate,  two  assays  being  always  made. 
It  permits  the  execution  of  several  titrations  without  the  necessity 
of  a  too  frequent  renewal  of  sodic  sulphide,  which  is  stored  in 
a  yellow  flask  of  large  capacity  supplying  two  MolirV.  burettes, 
under  which  the  beakers  can  be  placed  and  warmed.  A  mirror 


328  VOLUMETRIC  ANALYSIS.  §    78. 

shows  by  reflection  the  iron  flakes  which  settle  down  after  shaking 
the  liquid. 

Lunge  uses  for  the  indicator  paper  soaked  with  basic  ferric 
chloride,  strips  of  which  are  so  suspended  during  titration  that 
about  half  the  strip  dips  into  the  liquid. 

Too  much  stress  cannot  be  laid  upon  the  necessity  of  standard- 
izing the  sodic  sulphide  under  the  same  conditions  as  to  volume  of 
fluid,  proportions  of  NH3  and  HC1,  and  colour  of  the  indicator,  as 
will  actually  occur  in  the  analysis. 

5.      Estimation    as    Ferrocyanide. 

In  Acetic  Acid  Solution  (Galetti).  When  ores  containing  zinc 
and  iron  are  dissolved  in  acid,  and  the  iron  precipitated  with 
ammonia,  the  ferric  oxide  invariably  carries  down  with  it  a 
portion  of  zinc,  and  it  is  only  by  repeated  precipitation  that  the 
complete  separation  can  be  made.  In  this  process  the  zinc  is 
converted  into  soluble  acetate,  and  titrated  by  a  standard  solution 
of  potassic  ferrocyanide  in  the  presence  of  insoluble  ferric  acetate. 

The  Standard  Solution  of  Potassic  ferrocyanide,  as  used  by 
Galetti,  contains  41 '250  gm.  per  liter.  1  c.c.  =  0*01  gm.  Zn,  but 
its  actual  working  power  must  be  fixed  by  experiment. 

Standard  Zinc  Solution,  10  gm.  of  pure  metallic  zinc  per  liter 
dissolved  in  hydrochloric  acid. 

The  process  is  available  in  the  presence  of  moderate  quantities 
of  iron  and  lead,  but  copper,  manganese,  nickel,  and  cobalt  must 
be  absent. 

The  adjustment  of  the  ferrocyanide  solution  (which  should  be 
freshly  prepared  at  short  intervals)  must  be  made  in  precisely  the 
same  way,  and  with  the  same  volume  of  liquid  as  the  actual 
analysis  of  ores,  and  is  best  done  as  follows  : — 

25  c.c.  of  zinc  solution  are  measured  into  a  beaker,  15  c.c.  of  liquid 
ammonia  of  sp.  gr.  0'900  added  to  render  the  solution  alkaline,  then  very 
cautiously  acidified  with  acetic  acid,  and  50  c.c.  of  acid  ammonic  acetate 
(made  by  adding  together  20  c.c.  of  ammonia  of  sp.  gr.  0'900,  15  c.c.  of 
concentrated  acetic  acid  and  65  c.c.  of  distilled  water),  which  is  poured  into 
the  mixture,  then  diluted  to  250  c.c.,  and  warmed  to  about  50°  C.  The 
titration  is  then  made  with  the  ferrocyanide  solution  by  adding  it  from  a 
burette  until  the  whole  of  the  zinc  is  precipitated.  Galetti  judges  the 
ending  of  the  process  from  the  first  change  of  colour  from  white  to  ash  grey, 
which  occurs  when  the  ferrocyanide  is  in  excess  ;  but  I  prefer  to  ascertain  the 
ending  by  taking  drops  from  the  solution,  and  bringing  them  in  contact  with 
solution  of  uranic  acetate  on  a  white  plate  until  a  faint  brown  colour 
appears.  The  ferrocyanide  solution  should  be  of  such  strength  that 
measure  for  measure  it  agrees  with  the  standard  zinc  solution.  In  the 
present  case  25  c.c.  would  be  required. 

In  examining  ores  of  zinc,  such  as  calamine  and  blende,  Galetti  takes 
0'5  gm.  for  the  analysis,  and  makes  the  solution  up  to  500  c.c.  Calamine 
is  at  once  treated  with  HC1  in  sufficient  quantity  to  bring  it  into  solution. 


§  78.  ZINC.  329 

Blende  is  treated  with  aqua  regia,  and  evaporated  with  excess  of  HC1  to 
remove  nitric  acid.  The  solutions  of  zinc  so  obtained  invariably  contain 
iron,  which  together  with  the  zinc  is  kept  in  solution  by  the  HC1,  but  to 
insure  the  peroxidation  of  the  iron,  it  is  always  advisable  to  add  a  little 
potassic  chlorate  at  a  boiling  heat  during  the  extraction  of  the  ore.  The 
hydrochloric  solution  is  then  diluted  to  about  100  c.c.,  30  c.c.  of  ammonia 
added,  heated  to  boiling,  exactly  neutralized  with  acetic  acid,  100  c.c.  of  the 
acid  ammonic  acetate  poured  in,  and  diluted  to  about  500  c.c.  The  mixture 
as  prepared  will  contain  all  the  zinc  in  solution,  and  the  iron  will  be  pre- 
cipitated as  acetate.  The  titration  may  at  once  be  proceeded  with  at  a 
temperature  of  about  50°  to  60°  C.  by  adding  the  ferrocyanide  until  the 
necessary  reaction  with  uranium  is  obtained.  As  before  mentioned, 
Galetti  takes  the  change  of  colour  as  the  ending  of  the  process,  and  when 
iron  is  present  this  is  quite  distinguishable,  but  it  requires  considerable 
practice  to  rely  upon,  and  it  is  therefore  safer  to  use  the  uranium  indicator. 
When  using  the  uranium,  however,  I  prefer  to  dilute  the  zinc  solution  less, 
both  in  the  adjustment  of  the  standard  ferrocyanide  and  the  analysis  of 
ores.  The  dilution  is  necessary  with  Galetti's  method  of  ending  the 
process,  but  half  the  volume  of  liquid,  or  even  less,  is  better  with  the 
external  indicator. 

In  Hydrochloric  Acid  Solution  (Fahlberg  and  Maxwell  Lyte). 
This  method  is  not  available  in  the  presence  of  iron,  copper,  nickel, 
cobalt,  or  manganese. 

The  Standard  Solution  of  Ferrocyanide. — 1  c.c.  =  O01  gm.  of 
zinc.  Lyte  finds  that  this  is  obtained  by  dissolving  43*2  gm.  of 
pure  potassic  ferrocyanide  and  diluting  to  1  liter.  This  corresponds 
volume  for  volume  with  a  solution  of  10  gm.  of  pure  zinc  in  excess 
of  hydrochloric  acid  diluted  to  1  liter.  My  experiments  confirm 
this,  but  each  operator  is  advised  to  adjust  his  solutions  by 
experiment,  always  using  the  same  quantities  of  reagents  and 
volume  of  liquid.  The  end  of  the  reaction  between  the  zinc  and 
ferrocyanide  is  found  by  uranium. 

The  Analysis :  If  a  solution  of  zinc  freely  acidified  with  HC1  is  heated  to 
nearly  boiling  point,  two  or  three  drops  of  uranic  solution  added,  and  the 
ferrocyanide  delivered  into  the  mixture  from  a  burette,  white  zinc  ferro- 
cyanide immediately  precipitates,  and  as  the  drops  of  ferrocyanide  fall  into 
the  mixture,  a  brown  spot  of  uranic  ferrocyanide  appears,  but  disappears 
again  on  stirring  so  long  as  free  zinc  exists  in  solution.  The  moment  all 
the  zinc  is  converted  into  ferrocyanide,  the  addition  of  test  solution  tinges 
the  whole  liquid  brown.  This  addition  of  uranium  to  the  liquid  may  be 
used  as  a  guide  to  the  final  testing  on  a  porcelain  plate,  since  as  the  pre- 
cipitation approaches  completion,  the  tinge  of  brown  disappears  more 
slowly.  The  actual  ending,  however,  is  always  ascertained  by  spreading  a 
drop  or  two  of  the  liquid  upon  the  plate,  bringing  into  contact  with  it  a 
glass  rod  moistened  with  uranic  solution ;  when  the  same  shade  of  colour  is 
produced  as  occurred  in  the  original  titration  of  the  ferrocyanide  solution, 
the  process  is  ended. 

Lyte  gives  the  following  method  of  treating  a  blende  containing 
lead,  copper,  and  iron  (C.  N.  xxi.  222) : — 

2  gm.  of  finely  powdered  ore  were  boiled  with  strong  HC1  and  a  little 
KC1O3,  the  insoluble  matter  again  treated  in  like  manner,  the  solutions 
mixed  and  evaporated  somewhat,  washed  into  a  beaker,  cooled,  and  moist 


330  VOLUMETEIC  ANALYSIS.  §    78. 

baric  carbonate  added  to  precipitate  iron,  allowed  to  stand  a  few  hours,  then 
filtered  into  a  200  c.c.  flask  containing  10  c.c.  of  strong  HC1,  and  washed 
until  the  exact  measure  was  obtained.  20  c.c.  (=0'2  gm.)  of  blende  were 
measured  into  a  small  beaker,  diluted  with  the  same  quantity  of  water, 
3  drops  of  uranic  solution  added,  and  the  ferrocyanide  delivered  in  from 
a  burette.  When  70  c.c.  were  added  the  brown  tinge  disappeared  slowly ; 
the  testing  on  a  white  plate  was  then  resorted  to,  and  the  ferrocyanide 
added  drop  by  drop,  until  the  proper  effect  occurred  at  73  c.c.  As  a  slight 
excess  of  ferrocyanide  was  necessary  to  produce  the  brown  colour,  0*2  c.c. 
was  deducted,  leaving  72'8  c.c.  as  the  quantity  necessary  to  precipitate  all 
the  zinc.  The  0'2  gm.  of  blende  therefore  contained  0'0728  gm.  of  Zn  or 
36'4  per  cent. 

The  sample  in  question  contained  about  2 '7  per  cent,  of  copper, 
but  this  was  precipitated  with  the  iron  by  the  baric  carbonate ;  had 
it  contained  a  larger  quantity,  the  process  would  not  have  been 
available  unless  the  copper  was  removed  by  other  means. 

Fahlberg.(Z.  a.  C.  1874,  379)  estimates  the  zinc  in  hydro- 
chloric solution  with  ferrocyanide  and  uranic  indicator,  but 
recommends  the  addition  of  ammonic  chloride  to  the  extent  of 
about  five  times  the  weight  of  zinc  present.  With  the  well- 
known  retarding  effect  of  ammonia  salts  on  the  uranium  reaction, 
the  operator  must  be  careful  to  carry  out  his  analysis  precisely 
in  the  same  way  as  the  original  titration. 

Ores  containing  galena  or  copper  are  treated  with  aqua  regia,  then  boiled 
with  excess  of  HC1,  the  heavy  metals  precipitated  with  H2S  and  filtered  off, 
the  iron  peroxidized  with  HNO3  or  KC1O3,  cooled,  precipitated  with 
ammonia,  dissolved  and  re-precipitated  twice,  to  remove  all  zinc.  The 
ammoniacal  solutions  are  then  mixed,  neutralized  with  HC1,  10  or  15  c.c.  of 
concentrated  HC1  added,  then  titrated  with  ferrocyanide. 

Fah Ib erg  stated  in  his  original  paper  that  the  process  yields 
good  results  with  ores  containing  lead,  copper,  manganese,  and 
iron ;  but  this  is  certainly  not  true  as  to  manganese,  and  he  has 
since  acknowledged  the  fact.  He  states,  however,  that  if  moist 
brown  lead  dioxide  is  shaken  up  with  the  sulphuric  solution  of  Zn, 
the  whole  of  the  Fe  and  Mn  are  precipitated.  The  liquid  is 
filtered  off,  precipitate  washed,  then  nitrate  and  washings  titrated 
with  ferrocyanide. 

M  ah  on  (Amer.  Chem.  Journ.  iv.  53)  uses  the  ferrocyanide 
method  much  in  the  same  way  as  above  described,  but  finds  that 
Mn  must  be  absent  to  ensure  good  results.  In  the  presence  of 
Mn  he  separates  the  Zn  from  a  strong  acetic  solution  with  IPS. 
The  sulphide  is  then  dissolved  in  HC1  and  titrated  as  before. 

Technical  process  for  Ores  containing-  Iron. — Voigt  (Zeit.  ang.  Chem. 
1889,  307,  308).— The  solution  of  the  substance  in  hydrochloric  acid  is 
oxidized  with  nitric  acid  and  diluted  to  about  100  c.c.  Sufficient  potassic 
tartrate  to  keep  the  iron  in  solution  is  added,  and  then  ammonia  to  feeble 
alkalinity,  and  the  liquid  is  further  diluted  to  about  250  c.c.  Standard 
solution  of  potassic  ferrocyanide  is  then  run  in,  until  a  drop  of  the  mixture 
brought  in  contact  -with  strong  acetic  acid  develops  a  permanent  blue.  The 
ferrocyanide  is  of  suitable  strength  if  1  c.c.  is  equal  to  O'Ol  gm.  of  zinc. 
About  46  gm.  of  the  salt  is  dissolved  to  a  liter,  and  the  solution  is  standard- 
ized against  one  of  zinc  made  by  dissolving  12'461  gm.  of  zinc  oxide  in 


§  78.  ZINC.  331 

hydrochloric  acid  and  diluting  to  a  liter ;  10  c.c.  of  this  solution  is  mixed 
with  5  gm.  of  potassic  tartrate,  a  few  drops  of  ferric  chloride,  ammonia,  and 
water  to  250  c.c.,  and  should  require  10  c.c.  of  the  ferrocyanide.  An  essential 
condition  is  that  the  excess  of  ammonia  should  he  as  small  as  possible. 
Incorrect  results  are  obtained  when  much  manganese  is  present ;  lead  is  not 
injurious. 


6.     Estimation   of  Zinc   as   Oxalate. 

This  method  is  based  on  the  fact  that  all  the  metals  of  the 
magnesia  group  are  precipitated  in  the  absence  of  alkaline  salts  by 
oxalic  acid,  with  the  addition  of  alcohol.  The  cases  are  very  few 
in  which  such,  a  method  can  be  made  available,  but  the  process  as 
described  by  W.  G.  Leison  (Sill im aw' 8  Journ.  Sept.  1870) 
is  -here  given. 

The  zinc  compound  is  obtained,  preferably  as  sulphate,  in  neutral  solution, 
and  strong  solution  of  oxalic  acid  and  a  tolerable  quantity  of  strong  alcohol 
are  added.  Zinc  oxalate  quickly  separates  in  a  fine  crystalline  powder,  which 
when  washed  by  alcohol  from  excess  of  oxalic  acid  and  dried,  can  be  dissolved 
in  hot  dilute  sulphuric  acid,  and  titrated  with  permanganate ;  the  amount 
of  zinc  is  calculated  from  the  weight  of  oxalic  acid  so  found.  If  the  zinc 
oxalate  be  washed  on  a  paper  filter,  it  cannot  be  separated  from  the  paper 
without  contamination  with  fibres  of  that  material,  which  would  of  course 
affect  to  some  extent  the  permanganate  solution.  Hence  it  is  advisable  to 
filter  through  very  clean  sand,  best  done  by  a  special  funnel  ground  conical 
at  the  throat ;  into  this  is  dropped  a  pear-shaped  stopper  with  a  long  stem, 
the  pear-shaped  stopper  fitting  the  funnel  throat  tightly  enough  to  prevent 
sand  but  not  liquids  from  passing;  a  layer  of  sand  being  placed  upon  the 
globular  end  of  the  stopper  and  packed  closely,  the  liquid  containing  the 
oxalate  is  brought  upon  it  and  so  washed ;  finally  the  stopper  is  lifted,  the 
sand  and  oxalate  washed  through  with  dilute  acid  into  a  clean  flask,  and  the 
titration  completed. 


7.     Zinc   Dust. 

The  value  of  this  substance  depends  upon  the  amount  of  metallic 
zinc  contained  in  it ;  but  as  it  generally  contains  a  large  proportion 
of  zinc  oxide,  the  foregoing  methods  are  not  available  for  its 
valuation.  The  volume  of  hydrogen  yielded  by  it  on  treatment 
with  acids  appears  to  me  to  be  the  most  accurate,  as  suggested  by 
Fresenius  or  by  Barnes  (/.  S.  C.  I.  v.  145).  This  may  very 
well  be  done  in  the  nitrometer  with  decomposing  flask,  and 
comparing  the  volume  of  gas  yielded  by  pure  zinc  and  the  sample 
of  dust  under  examination. 

Weil  decomposes  a  known  volume  of  standard  solution  of 
copper  by  digesting  0*4  gm.  of  the  zinc  dust  in  a  platinum  capsule, 
with  50  c.c.  of  copper  solution  containing  0'5  gm.  Cu.  The  zinc 
precipitates  metallic  copper  equivalent  for  equivalent.  After 
removing  the  zinc  refuse  and  metallic  copper  by  filtration  and 
washing,  an  aliquot  portion  of  the  filtrate  is  titrated  with  standard 
tin  solution  for  the  excess  of  copper  as  described  in  §  54.6.  The 


332  VOLUMETRIC   ANALYSIS.  §    79. 

amount  of  Cu  precipitated,  when  multiplied  by  the  factor  1*0236, 
will  give  the  Zn  in  the  0*4  gm.  of  dust. 

Many  other  methods  have  been  proposed  for  the  valuation  of 
this  substance.  The  best  is  that  of  Klemp  (Z.  a.  C.  xxix.  253), 
which  consists  in  treating  the  dust  with  an  excess  of  caustic 
potash  and  potassic  iodate :  the  latter  is  reduced  in  definite  pro- 
portion by  the  metallic  zinc  to  potassic  iodide,  and  the  latter 
estimated  by  distillation  in  the  iodometric  apparatus,  fig.  29,  30, 
or  34.  The  solutions  of  potash  and  iodate  must  be  somewhat 
concentrated,  and  the  mixture  with  the  zinc  dust  must  be  intimate, 
which  may  be  best  secured  by  shaking  the  whole  together  in  a 
well-stoppered  200  c.c.  flask  with  glass  beads.  A  5  per  cent, 
solution  of  iodate  should  be  used,  and  the  potash  solution  should 
be  about  40  per  cent.  For  1  gm.  of  the  dust,  30  c.c.  of  the  iodate 
and  so  much  of  the  potash  solution  and  water  should  be  used  as  to 
measure  130  c.c.  The  weighed  substance,  together  with  the 
beads,  being  already  in  the  flask,  the  solutions  are  added,  the 
stopper  greased  with  vaseline,  tied  down  and  shaken  for  five 
minutes,  then  heated  on  the  water  bath,  with  occasional  shaking, 
for  one  hour.  The  flask  is  then  cooled  and  the  contents  diluted  to 
250  or  500  c.c.,  and  50  or  100  c.c.  placed  in  the  distilling  flask, 
acidified  with  sulphuric  acid,  and  the  iodine  so  set  free  distilled 
into  solution  of  potassic  iodide,  and  titrated  with  thiosulphate  in 
the  usual  way.  Each  0'2  gm.  of  iodine  so  found  =  0-25644  gm.  Zn. 


8.     Zinc    Oxide   and   Carbonate. 

Benedikt  and  Cantor  (Zeit.  angew.  Cliem.  1888,  236,  237) 
shew  that  zinc  oxide  and  carbonate  can  be  accurately  titrated  with 
standard  acid  and  alkali,  using  methyl  orange  as  indicator,  and 
other  zinc  salts,  using  phenolphthalein.  The  oxide  or  carbonate  is 
dissolved  in  excess  of  acid,  and  the  excess  titrated  back  by  soda 
solution.  Zinc  salts  are  dissolved  in  water  (50  c.c.  to  O'l  gm.  ZnO), 
phenolphthalein  is  added,  and  then  standard  soda  solution  to  intense 
red  colour.  A  few  more  c.c.  of  soda  are  then  added,  the  mixture  is 
boiled  for  some  minutes,  and  the  excess  of  soda  titrated.  If 
either  free  acid  or  zinc  oxide  is  present  in  the  zinc  salt,  it  is 
neutralized  in  presence  of  methyl  orange  by  alkali  or  acid,  as  the 
case  may  be. 

% 

VANADIUM. 
V=51'2. 

§  79.  VANADIUM  salts,  or  the  oxides  of  this  element,  may  be 
very  satisfactorily  titrated  by  reduction  with  a  standard  ferrous 
solution;  thus — 

2FeO  +  V05=Fe203  +  VO4. 


§    79.  VANADIUM.  333 

1  gm.  of  Fe  represents  1*630357  gm.  of  vanadic  pentoxide. 

Lindemann  (Z.  a.  C.  xviii.  99)  recommends  the  use  of  a 
solution  of  ferrous  ammonio-sulphate  (double  iron  salt)  standardized 
by  _N_.  potassic  bichromate. 

Of  course  it  is  necessary  that  the  vanadium  compound  should  be 
in  the  highest  state  of  oxidation,  preferably  in  pure  sulphuric  acid 
solution.  The  blue  colour  of  the  tetroxide  in  the  dilute  liquid  has* 
no  misleading  effect  in  testing  with  ferridcyanide. 

With  hydrochloric  acid  great  care  must  be  taken  to  insure 
absence  of  free  Cl  or  other  impurities.  The  end-point  in  the  case 
of  this  acid  is  different  from  that  with  sulphuric  acid,  owing  to  the 
colour  of  the  ferric  chloride,  the  mixture  becoming  clear  green. 

The  accuracy  of  the  reaction  is  not  interfered  with  by  ferric  or 
chromic  salts,  alumina,  fixed  alkalies,  or  salts  of  ammonia. 

Vanadic  solutions  being  exceedingly  sensitive  to  the  action  of 
reducing  agents,  great  care  must  be  exercised  to  exclude  dust 
or  other  carbonaceous  matters,  alcohol,  etc. 


334  VOLUMETRIC  ANALYSIS.  §    80. 


APPENDIX  TO   PAKT  Y. 

BORIC    ACID    AND    EQUATES. 
Boric  anhydride  B203=70. 

§  80.  THE  soda  in  borax  may,  according  to  Thompson,  be 
very  accurately  estimated  by  titrating  the  salt  with  standard  H2S04 
and  methyl  orange  or  lacmoid  paper.  Litmus  and  phenacetolin 
give  very  doubtful  end-reactions :  phenolphthalein  is  utterly  useless. 

Example  :  1*683  gm.  sodic  pyroborate  in  50  c.c.  of  water  required  in  one 
case  16*7  c.c.  normal  acid,  and  in  a  second  16'65  c.c.  The  mean  of  the  two 
represents  0  517  gm.  Na2O.  Theory  requires  0*516  gm. 

Since  borates  are  now  much  used  as  preservative  agents,  a 
method  which  may  be  relied  upon  for  technical  purposes  will  be  of 
considerable  service,  and  such  is  described  by  E.  F.  Smith  (Amer. 
Cliem.  Journ.  1882).  The  process  depends  on  the  fact,  that  if  a 
solution  of  manganese  sulphate  is  added  to  one  of  borax,  then 
alcohol  in  equal  volume,  a  white  flocculent  precipitate  of  MnB407 
separates,  which  is  insoluble  in  the  alcoholic  liquid.  The  excess  of 
manganese  sulphate  is  then  determined  after  expulsion  of  the 
alcohol  by  permanganate,  according  to  Guyard's  or  Volhard's 
method  (§64. 2). 

Example:  10  c.c.  of  borax  solution  containing  O'l  gm. ;  to  this  were 
added  10  c.c.  of  solution  of  manganese  sulphate  containing  0*06  gm.  MnSO4 
and  20  c.c.  of  strong  alcohol.  The  mixture  was  well  stirred,  covered  up,  and 
allowed  to  stand  for  half  an  hour ;  then  filtered  (best  with  suction  pump) 
and  well  washed  with  alcohol.  Filtrate  and  washings  then  evaporated  to 
dry  ness  in  a  platinum  or  porcelain  basin. 

The  residual  Mn  was  then  dissolved  in  water,  some  strong  solution  of  zina 
sulphate  added,  heated  near  to  boiling,  and  permanganate  delivered  in  from 
a  burette  until  a  permanent  pink  colour  was  produced.  The  strength  of  the 
permanganate  was  such  that  18*5  c.c.=10  c.c.  of  MnSO4  solution  by  the 
same  method  of  titration.  The  amount  of  MnSO4  so  found  deducted  from 
that  originally  added  gave  the  amount  combined  with  the  boracic  acid. 

In  this  instance  6'4  c.c.  of  permanganate  were  required=0'0207  gm., 
showing  0*0393  gm.  to  be  combined=36'44  per  cent.  B203.  Theory  requires 
36'6  per  cent. 

A  mean  of  eighteen  determinations  gave  36*5  per  cent,  of  B203 
in  the  sample  of  pure  borax.  The  method  is  therefore  very  fairly 
accurate  for  soluble  borates. 

In  estimating  the  boracic  acid  in  insoluble  borates,  as  tourmaline, 
the  following  course  was  pursued  : — 

The  finely  pulverized  substance  was  fused  with  a  weighed  quantity  of  pure 
sodic  carbonate,  the  fused  mass  exhausted  with  water,  and  to  the  filtrate 


§    80.  BORATES.  335 

containing  all  the  sodic  borate,  together  with  some  silicate  and  aluminate, 
was  added  an  amount  of  pure  ammonic  sulphate  molecularly  equivalent 
to  the  sodic  carbonate.  The  solution  was  then  digested  until  all  the  ammonia 
was  expelled  and  the  volume  of  the  liquid  largely  reduced.  Any  silica  or 
alumina  which  had  separated  was  now  filtered  off,  and  the  precipitate 
thoroughly  washed  with  hot  water.  The  solution,  again  reduced  in  volume 
and  containing  only  the  borate  and  sulphates  of  sodium  and  ammonium, 
was  mixed  with  a  definite  amount  of  a  manganese  sulphate  solution  (strength 
previously  determined),  alcohol  added,  and  after  standing  one  half-hour  the 
borate  was  removed  by  filtration,  the  filtrate  evaporated  to  dryness,  and  the 
residue  carefully  ignited  to  expel  the  ammonium  salt.  The  manganese 
sulphate  left  was  dissolved  in  water,  and  the  titration  carried  out  as  before 
described. 

In  a  specimen  of  tourmaline  from  New  York  the  boracic  acid 
found  by  this  method  was  9 '7  per  cent.  Another  portion  of  the 
same  material  with  Marignac's  method  yielded  10  per  cent.  B203. 
In  another  tourmaline  (locality  unknown)  two  determinations  by 
this  method  gave  6*55  and  6*32  per  cent.  B203,  while  with 
Marignac's  method  the  amount  obtained  was  6 '8  per  cent.  B203. 

In  some  instances  upon  evaporating  the  alcoholic  solution 
preparatory  to  determining  the  excess  of  manganese  sulphate, 
brownish  flocks  separated.  These  were  always  dissolved  in  a  little 
sulphuric  acid  and  then  evaporated  to  dryness. 

It  is  perhaps  hardly  necessary  to  say  that  some  delicacy  of 
manipulation  is  necessary  in  carrying  out  this  process,  especially 
if  very  small  quantities  are  dealt  with. 

A  rapid  and  fairly  accurate  estimation  of  free  boric  acid  may  be  made 
as  suggested  by  Will  (Arch.  Pkarm.  [3],  25, 1101—1113),  by  titration  with 
a  standard  baryta  solution,  which  is  added  to  the  solution  of  the  acid  until 
the  turbidity  appearing  at  first  is  completely  and  exactly  removed.  The 
amount  of  baric  hydroxide  used  is  exactly  double  the  equivalent  of  the 
boric  acid  present,  according  to  the  equation  4H3BO3-j-Ba  (HO)2=BaB4O7-f 
7H2O.  Schwarz  has  recently  shown  that  the  boric  acid  set  free  from 
borax  by  nitric  acid  does  not  affect  Congo-red,  whilst  the  slightest  excess  of 
nitric  acid  produces  a  blue-violet  tint,  and  on  this  has  based  an  obvious 
method  for  estimating  the  amount  of  acid  in  the  borax.  The  boric  acid 
thus  set  free  may  also  be  determined  by  titration  with  baryta  water  as  above, 
or  ethyl  or  methyl  orange  may  be  substituted  for  the  Congo-red,  and  hydro- 
chloric acid  may  be  used  to  decompose  the  borax.  A  mixture  of  free  boric 
acid  and  borax  solution  may  be  dealt  with  by  a  combination  of  the  two 
methods,  that  is,  by  first  titrating  with  standard  acid,  and  then  titrating  the 
total  boric  acid  with  baryta  water.  Instead  of  first  setting  free  the  acid, 
a  solution  of  pure  borax  can  be  titrated  directly  by  baryta  solution,  but  only 
half  the  amount  of  standard  solution  is  now  required,  since  the  equivalent 
amount  of  sodic  hydroxide  set  free  replaces  the  other  half  of  baryta. 

In  the  presence  of  borax,  chlorides  can  be  estimated  directly  by  means 
of  silver  nitrate,  using  potassic  chromate  as  indicator ;  free  boric  acid 
interferes  with  the  reaction  in  this  case ;  the  free  acid  is  first  determined  by 
means  of  baryta  solution ;  then  normal  soda  solution  equivalent  to  at  least 
half  the  baryta  solution  employed  is  added,  and  then  dilute  sulphuric  acid 
until  neutral ;  the  chlorides  can  now  be  directly  estimated.  The  addition  of 
soda  solution  may  be  omitted  when  estimating  chlorides  in  the  presence  of 
little  free  boric  acid  and  much  borax,  just  as  in  the  presence  of  borax  only. 


336  VOLUMETRIC   ANALYSIS.  §    81. 

Of  course,  the  chlorides  and  boric  acid  can  be  determined  in  separate 
portions,  and  can  be  directly  titrated.  The  chlorides  after  neutralization 
by  means  of  soda  solution. 

Boric  acid  in  presence  of  sulphates  is  estimated  by  the  aid  of  phenacetolin 
as  indicator.  To  the  solution  of  boric  acid  and  sulphates,  two  drops  of  an 
alcoholic  solution  of  the  indicator  are  added,  and  then  standard  baryta 
solution  until  a  faint  yellow  tint  appears  ;  normal  hydrochloric  acid  is  now 
added  until  a  faint  rose  tint  becomes  a  decided  rose  colour,  the  corresponding 
amount  of  baryta  solution  is  deducted  from  the  original  amount  taken,  and 
the  remainder  indicates  the  boric  acid.  A  further  addition  of  hydrochloric 
acid  until  the  colour  changes  from  rose  to  yellow  with  the  last  drop,  serves 
as  a  control  estimation ;  the  acid  thus  taken  being  equivalent  to  the  baryta 
combined  with  the  boric  acid.  Halving  the  baryta  and  calculating  the 
equivalent  boric  acid,  this  should  agree  with  the  amount  first  formed. 
Sulphates  of  the  alkalies  and  of  the  alkaline  earths,  excepting  magnesia,  may 
be  present.  A  little  practice  is  required  to  get  the  rose  colour  accurately, 
and  it  is  found  better  to  use  normal  acid  rather  than  a  weaker  one.  For 
the  estimation  of  borax  in  the  presence  of  sulphates,  Schwarz's  method 
may  be  directly  applied. 


OILS    AND    FATS. 

§  81.  THE  examination  of  fatty  matters  by  titration  of  their 
soluble  or  volatile  and  total  fatty  acids  has  of  late  assumed  very 
considerable  importance,  in  view  of  furnishing  results  which  aid 
in  determining  the  amount  of  adulteration  to  which  they  are 
subject.  It  has  been  found  especially  serviceable  in  the  case  of 
butter,  and  two  methods  are  in  vogue,  both  of  which  give  good 
technical  results.  The  same  methods  are  more  or  less  available  for 
the  examination  of  fats  other  than  butter;  and  further  experi- 
ments by  various  operators  have  rendered  the  methods  of  value  for 
differentiating  various  fatty  bodies.  The  titration  methods  were 
originated  by  Koettstorfer  (Z.  a.  C.  xix.  199)  and  Eeichert 
(Zi.  a.  C.  xviii.  68),  both  being  based  on  suggestions  originating 
with  the  veteran  chemist  Chevreul,  and  by  Hehner  and  Angell 
in  their  well-known  treatise  on  Butter  Analysis. 

The  same  may  be  said  to  a  great  extent  of  another  novel  and 
interesting  method  of  examining  the  nature  and  composition  of 
various  fats,  by  the  power  they  possess  of  absorbing  bromine  or 
iodine.  This  method,  as  regards  bromine,  has  been  worked  out 
with  considerable  diligence  and  ability  by  Mills  and  Siiodgrass 
(/.  S.  C.  I.  ii.  435  and  ibid  iii.  366),  also  by  Allen  (ibid  v.  68, 
also  in  his  well-known  treatise  on  Organic  Analysis).  The  iodine 
method  of  Hubl  is  described  in  J.  S.  C.  I.  iii.  641.  These 
various  methods  have  been  most  voluminously  discussed  in  their 
chemical  and  practical  aspects,  so  that  it  must  suffice  here  to  give 
shortly  the  methods  of  analysis.  It  is  only  perhaps  necessary  to 
say  that  Hubl's  iodine  method  is  now  generally  adopted  in 
preference  to  the  absorption  by  bromine. 


§    81.  OILS   AND    FATS.  337 

Butter. 

Reichert's  Method. — This  consists  in  saponifying  the  fat  to  be 
examined  by  an  alkali,  separating  the  fixed  acids  by  neutralizing 
the  alkali,  and  distilling  off  the  volatile  acids  (chiefly  butyric)  for 
titration  with  standard  acid.  In  this  and  Koettstorfer's  method, 
where  also  alcoholic  solution  of  caustic  alkali  is  used,  it  is  essential 
to  avoid  absorption  of  CO2  by  long  exposure. 

The  Analysis :  2'5  gm.  of  the  sample,  aftar  melting  on  the  water  bath, 
allowing  the  water  to  settle  and  filtering  through  a  dry  filter,  are  weighed 
into  a  flask  holding  about  160  c.c.,  and  to  it  is  added  a  sufficiency  of 
alcoholic  solution  of  potash  to  saponify  the  fat  on  heating  in  the  water 
bath.  25  c.c.  of  solution  of  about  |  strength  is  generally  sufficient.  Close 
the  flask  with  a  cork  fitted  with  a  long  vertical  tube,  and  continue  the  heating 
in  the  water  bath  until  perfect  solution  is  obtained,  then  transfer  the  liquid 
to  a  porcelain  or  glass  basin,  and  heat  in  the  bath  till  the  alcohol  is  completely 
evaporated.  The  residue  is  then  dissolved  in  about  50  c.c.  of  water, 
transferred  back  to  the  flask,  dilute  H2SO4  added  in  moderate  excess,  then 
diluted  with  water  to  about  75  c.c.  Some  small  pieces  of  pumice  strung 
together  with  intervening  small  spirals  of  thin  platinum  wire  are  then  placed 
in  the  liquid,  the  flask  connected  with  a  small  condenser,  and  the  liquid 
distilled  on  a  small  sand  bath  until  at  least  two-thirds  of  its  volume  have 
been  collected.  The  distillate  is  then  filtered  if  necessary,  and  carefully 
titrated  with  •£$•  soda  or  potash,  using  phenolphthalein  as  indicator. 

The  distillate  from  2 '5  gm.  of  a  genuine  butter  requires, 
according  to  all  experience,  not  less  than  12 '5  c.c.  of  —^  alkali, 
when  the  method  is  conducted  as  above  described.  Higher  figures 
may  doubtless  be  obtained  by  carrying  the  distillation  still  further. 
Keichert  himself  obtained  an  average  of  14  c.c.  in  the  case  of 
pure  butters  ;  but  his  paper  describes  the  details  of  the  process  so 
imperfectly,  that  a  doubt  is  left  as  to  how  far  the  distillation  was 
carried.  If  the  number  of  c.c.  of  acid  used  is  to  be  expressed  in 
terms  of  butyric  acid  the  factor  0*352  may  be  used  (Allen),  and 
in  the  case  of  requiring  12 '5  c.c.  of  acid  with  2 '5  gm.  of  butter 
the  resulting  figure  is  4*41.  The  results  of  many  operators  reduced 
in  this  way  show  from  4*41  to  4 '96,  but  none  of  them  fell  below 
the  former  number,  which  may  therefore  be  taken  as  the  inferior 
limit.*  Butter  from  goats'  and  ewes'  milk  gave  practically  the 
same  results,  while  butterine  or  oleomargarine  gave  in  no  case 
higher  than  0'5,  and  generally  much  less.  Cocoanut  oil,  among  the 
possible  adulterants  of  butter,  gave  the  highest  figure,  viz.,  1-15 
(Moore);  but  this  is  so  far  below  the  figure  for  butter,  that  even 
a  very  large  admixture  could  at  once  be  detected.  It  may  be 
remarked  that  the  exact  weighing  of  2*5  gm.  of  butter  into 
a  flask,  especially  if  not  solidified,  is  a  difficult  operation;  it  is 

*  Instead  of  expressing  the  result  in  terms  of  butyric  acid  (eq.  =  88),  All  en  advises 
the  statement  of  the  weight  of  KHO  neutralized  by  the  distillate  from  100  gm.  of 
fat.  This  is  obtained  by  multiplying  the  volume  of  ^  solution  neutralized  by  the 
distillate  from  2'5  gm.  of  fat  by  0-2241.  This  gives  the  percentage  by  weight  of  KHO 
required  by  the  fat. 

Z 


338  VOLUMETRIC   ANALYSIS.  §    81. 

therefore  advisable  to  operate  with  about  this  quantity,  noting 
the  exact  weight,,  and  arriving  at  a  comparative  result  by 
calculation. 

The  method  above  described  is  sufficiently  accurate  in  the 
majority  of  cases,  but  Wo  liny  has  shown,  by  a  long  and  careful 
series  of  experiments  (Bied.  Centr.  1887,  699,  also  Analyst,  xii.  203), 
that  there  are  sources  of  error  which  must  be  removed  before 
absolutely  accurate  results  can  be  secured.  The  chief  of  these 
he  ascribes  to  carbonic  acid,  which  may  at  any  time  be  present 
in  the  alcoholic  potash.  He  therefore  uses  a  50  per  cent,  aqueous 
solution  of  soda  in  place  of  the  potash,  and  prefers  baryta  solution 
for  the  final  titration. 

In  order  to  avoid  exposure  to  the  air  during  the  saponification, 
and  also  loss  of  volatile  acids,  Wollny  devised  the  following 
arrangement.  A  condenser  slanting  upward  at  an  angle  of  45°  is 
fixed  near  the  water  bath  upon  which  the  saponification  is  to 
take  place.  The  flask  is  connected  with  the  condenser  by  means 
of  a  "|~-piece  and  india-rubber  tubes,  so  that  the  leg  of  the  T-piece 
can  be  directed  upward  or  downward  as  desired.  During  saponifi- 
cation, which  should  take  half  an  hour  on  the  boiling  water  bath, 
the  leg  of  the  "[~~piece  *s  directed  upward,  being  closed  with  a 
short  piece  of  india-rubber  and  glass  rod.  The  alcohol  in  this 
manner  runs  back  into  the  flask.  After  that  time  the  "]~~piece 
is  turned  downward  and  opened  :  the  alcohol  can  thus  be  collected 
in  a  flask  standing  beneath.  After  twenty  minutes,  when  distillation 
is  complete,  the  ~]~"piece  ig  again  turned  upwards,  arid  through  it 
100  c.c.  of  boiling  water  are  run  into  the  flask  by  means  of  a 
pipette  being  tightly  joined  to  the  short  piece  of  india-rubber. 
The  "|""piece  is  closed  again  until  the  soap  is  completely  dis- 
solved in  the  water,  solution  being  assisted  by  gently  shaking 
the  flask. 

The  Analysis :  5  gm.  of  the  clear  butter  fat  are  accurately  weighed  into  a 
300  c.c.  flask  (round  form,  length  of  neck  7  or  8  centimeters,  width  of  neck 
2  centimeters),  2  c.c.  of  50  per  cent,  soda  solution  (which  must  be  preserved 
so  that  carbonic  acid  cannot  be  absorbed),  and  10  c.c.  of  96  per  cent,  alcohol, 
are  added,  and  the  mixture  is  heated  under  a  reflux  condenser  for  fifteen 
minutes  in  a  boiling  water  bath.  The  alcohol  is  then  distilled  off  whilst 
the  flask  is  heated  for  at  least  half  an  hour ;  100  c.c.  of  boiling  water  are 
added  under  due  precautions,  and  the  flask  heated  until  the  soap  is  completely 
dissolved.  40  c.c.  of  sulphuric  acid  (25  c.c.  H2SO4  in  1  liter)  and  two 
pieces  of  pumice  of  the  size  of  a  pea  are  added,  and  the  flask  is  at  once 
connected  with  a  condenser  by  means  of  a  glass  tube,  7  centimeters  wide, 
and  having,  at  a  distance  of  1  centimeter  above  the  cork,  a  bulb  of  a  diameter 
of  2—2-5  centimeters.  The  tube  is  bent  immediately  above  the  bulb 
upward  in  an  oblique  angle,  in  which  direction  it  extends  for  5  centimeters, 
and  is  then  again  bent  downward,  also  in  oblique  angle,  and  then  connected 
with  a  condenser  by  means  of  an  india-rubber  tube.  The  flask  is  then 
heated  by  means  of  a  very  small  flame,  until  the  insoluble  fatty  acids  are 
completely  fused ;  110  c.c.  are  then  distilled  off  into  a  graduated  flask,  the 
distillation  lasting  thirty  minutes ;  the  distillate  is  mixed,  and  100  c.c.  filtered 
oft'.  This  is  transferred  into  a  beaker,  1  c.c.  of  phenolphthalein  solution. 


§    81.  OILS  AND   FATS.  339 

(5  gm.  in  1  liter  50  per  cent,  alcohol)  added  and  titrated  with  decinormal 
baryta  solution.  To  the  volume  of  baryta  used  one-tenth  is  added,  and  the 
figure  obtained  by  blank  experiment  is  subtracted;  the  latter  should  not 
amount  to  more  than  0'33  c.c. 

Koettstorfer's  Method. — This  operation  estimates  the  saponi- 
fying equivalent  of  any  fatty  substance,  but  is  allowed  on  all 
hands  to  be  less  satisfactory  in  discriminating  mixtures  of  other 
fats  with  butter,  although  extremely  useful.  In  this  method  the 
whole  of  the  acids  existing  in  the  fat  are  estimated.  The  solutions 
required  are  the  following : — 

Standard  Hydrochloric  Acid. — Semi-normal  strength,  i.e.,  18'185 
gm.  per  liter. 

Standard  Solution  of  Caustic  Potash  in  Alcohol. — Methylated 
spirit,  previously  digested  with  permanganate,  dehydrated  with  dry 
potassic  carbonate,  then  distilled,  rejecting  the  first  portions,  may 
be  used  in  place  of  pure  alcohol.  In  any  case  the  strength  should 
not  be  less  than  90  per  cent.,  and  the  solution  should  be  freshly 
made  to  avoid  any  deep  colouration  likely  to  interfere  with  the 
indicator.  As  it  rapidly  changes  in  strength,  it  is  not  possible  to 
rely  upon  its  being  semi-normal,  but  it  should  be  roughly  adjusted 
at  about  that  strength  with  absolutely  accurate  hydrochloric  acid, 
and  a  blank  experiment  made  side  by  side  with  each  titration  of 
fat.  The  excess  of  potash  used  in  the  fat  titration  is  thus  expressed 
in  terms  of  §-  acid,  and  to  arrive  at  the  percentage  of  potash  each 
c.c.  is  multiplied  by  0*02805.  The  saponification  equivalent  of 
the  fat  or  oil  is  found  by  dividing  the  weight  in  milligrams  of  the 
sample  by  the  number  of  c.c.  of  normal  (not  *)  acid  corresponding 
to  the  alkali  neutralized  by  the  oil.  If  the  percentage  of  potash 
is  known,  the  saponifying  equivalent  may  be  found  by  dividing 
this  percentage  into  5610,  or  if  2s"aHO  is  the  alkali  used, 
into  4000. 

The  Analysis:  Prom  2  to  2' 5  gm.  of  the  fat,  previously  purified  by 
melting  and  filtration,  are  carefully  weighed  into  a  flask  fitted  with  vertical 
tube.  25  c.c.  of  standard  potash  are  then  added,  the  mixture  heated  on  the 
water  bath  to  gentle  boiling,  with  occasional  agitation,  until  a  perfectly  clear 
solution  is  obtained .  Koettstorfer  recommends  heating  for  fifteen  minutes ; 
but  in  the  case  of  butters  this  is  generally  more  than  sufficient ;  with  other 
fats  twenty  minutes  to  half  an  hour  may  be  required.  At  the  end  of  the 
saponification  the  flasks  are  removed  from  the  bath,  a  definite  and  not  too 
small  a  quantity  of  phenolphthalein  added,  and  the  titration  carried  out  with 
as  little  exposure  to  the  air  as  is  possible. 

The  method  of  calculation  adopted  by  Koettstorfer  is  to 
ascertain  the  number  of  milligrams  of  KHO  required  to  saturate 
the  acids  contained  in  1  gm.  of  fat,  or,  in  other  words,  parts 
per  1000.  He  found  that,  operating  in  this  way,  pure  butters 
required  from  221 '5  to  232 '4  m.gm.  of  KHO  for  1  gm.,  whereas 
the  fats  usually  mixed  with  butter,  such  as  beef,  mutton,  and  pork 

z  2 


340 


VOLUMETRIC  ANALYSIS. 


§    81. 


fat,  required  a  maximum  of  197  m.gm.  for  1  gm.,  and  other  oils 
and  fats  much  less. 

Practically  this  means  that  the  amount  of  KHO  required  for 
genuine  butters  ranges  from  23 '24  to  22 '15  per  cent.,  the  latter 
being  the  inferior  limit.  If  caustic  soda  is  used  instead  of  potash, 
other  numbers  must  of  course  be  used. 

My  experience,  and,  I  believe,  also  that  of  others,  shows  that 
the  method  cannot  be  depended  upon  in  the  case  of  old  re-melted 
butters,  although  perfectly  genuine. 

The  following  list  shows  the  parts  of  KHO  required  per  1000 
of  fat ;  the  first  four  being  calculated  from  their  known  equivalents, 
the  rest  obtained  experimentally  by  Koettstorfer,  Allen, 
Stoddart,  or  Archbutt: — 


Tripalmitin 
Tristearin 
Triolein 
Tributyrin 
Cocoanut  Oil 
Dripping 
Lard   . 
Horse  Pat 
Lard  Oil 
Olive  Oil 
Niger  Oil 


208-8 

Linseed 

189-1 

Cotton  Seed 

190-4 

Whale  . 

557-3 

Seal      . 

270-0 

Colza  and  E 

pe 

197-0 

Cod  Oil 

195-6 

Pilchard 

199-4 

Castor  . 

191—196 
191—196 

Sperm  . 
Shark  . 

189—191 

189—195 
191—196 
190—191 
191—196 
175—179 
182—187 
186—187 
176—178 
130—134 
84-5 


A  further  application  of  this  method  may  be  made  in  estimating 
separately  the  amounts  of  alkali  required  for  saturating  the  free 
fatty  acids  and  saponifying  the  neutral  glycerides  or  other  ethers 
of  any  given  sample  of  fat,  oil,  or  wax  (see  Allen,  Organic 
Analysis  ii.  45,  76). 


Titration  of  Miscellaneous  Oils  and  Fats  with  Bromine  or  Iodine. 

The  best  method  of  carrying  out  this  examination  as  regards 
bromine,  appears  to  be  that  of  Mills  and  Snod grass,  to  which 
reference  has  previously  been  made.  The  idea  of  using  bromine 
is  by  no  means  new.  Cailletet  in  1857  adopted  such  a  method; 
but  the  difficulty  then,  and  up  to  the  time  when  the  task  was 
undertaken  by  the  operators  mentioned,  was  the  accurate  measure- 
ment of  the  excess  of  bromine  used,  and  the  adaptation  of  such 
a  solvent  for  both  the  fats  and  the  bromine  as  would  exclude  the 
presence  of  water,  and  the  tendency  to  form  substitution  products 
of  variable  and  unknown  character  in  preference  to  merely  additive 
products. 

Our  knowledge  of  the  exact  composition  of  the  great  family  of 
fats  and  oils  is  at  present  limited,  and  it  is  not  possible  to  make 
this  reaction  possess  any  strict  chemical  valency ;  but  experiment 
has  shown  that  there  are  certain  well-defined  fats  which  absorb 


§    81.  OILS  AND   FATS.  341 

within  a  very  narrow  limit  the  same  amount  of  the  halogen  under 
the  same  conditions,  and  hence  the  method  may  be  made  highly 
suggestive  as  to  mixtures  of  various  fats  whose  absorption  powers 
have  been  observed. 

In  the  first  instance  the  common  solvent  used  for  the  fat 
and  the  bromine  was  carbon  disulphide ;  but  although  very  good 
results  Avere  obtained,  compared  -with  solvents  previously  tried  by 
other  operators,  there  were  the  drawbacks  of  its  offensive  smell, 
and  the  solutions  of  bromine  in  it  did  not  possess  much  stability. 
Finally,  Dr.  Mills  adopted  carbon  tetrachloride  as  the  medium 
with  the  happiest  effects;  and  it  was  found  that  the  bromide 
solution  could  be  preserved  for  at  least  three  months  without 
diminution  of  standard.  On  the  other  hand,  by  using  this 
medium,  there  is  the  necessity  of  working  with  greater  delicacy, 
since  the  presence  of  the  merest  trace  of  water  has  more  effect  in 
producing  substitution  compounds  than  in  the  case  of  the  disulphide. 
The  accurate  estimation  of  the  excess  of  bromine,  after  the  absorp- 
tion is  complete,  is  necessarily  a  matter  of  great  importance ;  and 
this  can  be  done  either  by  comparison  of  colour  with  bromine  solu- 
tion of  known  strength  (the  least  effective  method)  $  or"  by  titratioii 
with  thiosulphate,  using  starch  and  potassic  iodide  as  the  indicator, 
which  is  better.  But,  best  of  all,  the  operators  after  long  research 
found  that  by  using  (3  naphthol  (a  substance  which  is  readily  and 
cheaply  obtainable,  and  which  forms  in  the  presence  of  carbon 
tetrachloride  a  mono-bromo  derivative)  they  could  construct  a 
solution  of  corresponding  strength  to  the  standard  bromine,  and 
thus  titrate  back  in  the  same  way  as  is  commonly  practised  in 
alkalimetry.  Very  fair  results  were  obtained  colorimetrically  by 
adopting  the  device  of  interposing  a  stratum  of  chromate  solution 
(page  128),  so  as  to  neutralize  the  yellow  colour  produced  with 
some  of  the  fish  oils,  and  which  tended  to  mask  the  red  colour  of 
the  bromine.  Experiments  showed  that,  using  a  bromine  solution 
having  a  mean  standard  of  0*00644  gm.  per  c.c.,  the  average 
probable  error  per  cent,  in  a  single  result,  when  adopting  the  colour 
method  or  the  thiosulphate  and  iodine  was  0'62,  whereas  with 
/3  naphthol  it  was  reduced  to  0*46.  But  it  is  hardly  necessary  to 
say  that,  using  such  a  small  portion  of  material  as  is  absolutely 
necessary  in  order  to  avoid  secondary  results,  considerable  care 
and  practice  are  required.  The  sample  of  oil  or  fat  must  be  dried 
as  completely  as  possible,  by  heating  and  subsequent  filtering 
through  dry  scraps  of  bibulous  paper,  or  through  dry  double  filters, 
before  being  weighed. 

The  Analysis:  O'l  to  0*2  gm.  of  the  fat  is  dissolved  in  50  c.c.  of  the 
tetrachloride  and  standard  bromine  added,  until  at  the  end  of  15  minutes 
there  is  a  permanent  red  colour.  If  the  colorimetric  method  is  used, 
50  c.c.  of  tetrachloride  is  tinted  with  standard  bromine  to  correspond.  If 
the  iodine  re-action,  the  solution  of  brominated  material  is  added  to  potassic 
iodide  and  starch,  and  y^-  sodic  thiosulphate  delivered  in  from  a  burette  till 


342 


VOLUMETRIC   ANALYSIS. 


81. 


the  colour  is  discharged.  If,  on  the  other  hand,  the  standard  naphthol 
solution  is  used,  it  is  also  cautiously  added  from  a  burette  until  the  colour  is 
removed.  It  is  imperative  that  the  operations  in  all  cases  be  carried  on  out 
of  direct  sunlight.  If  the  operator  is  unable  to  use  carbon  tetrachloride,  the 
disulphide  may  be  used ;  but  the  solution  of  bromine  in  this  medium  is  less 
stable,  and  must  be  checked  more  frequently.  Somewhat  larger  portions  of 
oil  or  fat  may  however  be  used  for  the  analysis. 

It  may  be  of  service  to  give  some  few  of  the  results  obtained 
by  Mills  and  Snodgrass. 


Absorption    per    cent.— 


OILS. 

FATS. 

WAXES. 

Almond  (from 

Beef       -            -  35-01 

Beeswax             -    O'OO 

bitter   fruit)  26'27 

Butter  (fresh)    -  27'93 

Carnauba           -  33'50 

Do.  (from  sweet)  5374 

Do.   (commercial)  25'0 

Japan  (1)           -    2'33 

Cod        -            -  83-00 

Butterine  Scotch  36'32 

Do.       (2)           -     1-53 

Nut        -            -  30-24 

Do.  (Trench)      -  39'7l 

Myrtle  -            -    6'34 

Ling  Liver         -  82  '44 

Cocoanut            -    5*70 

Mustard             -  46'15 

Vaseline             -    5'55 

Neatsfoot           -  38'33 

Stearic  Acid       -    O'OO 

Olive      -            -  60-61 

Lard      -            -  37'29 

Palm      -            -  35-00 

Seal        -            -  57-34 

Whale   -            -30-92 

Linseed  -            -  76'09 

Mineral  Oil        -  30'31 

Shale  Oil          ) 

according  to  >  22  to  12 

sp.  gr.            J 

Aniline  -            -  169'8 

Turpentine  (dry)  236'0 

The  same  operators  determined  the  percentage  absorption  by 
pure  anhydrous  turpentine,  aniline  and  olive  oil  purified  by 
filtration  after  long  standing  at  low  temperature.  The  calculated 
values  are  based  on  the  known  ratios  — 


CioHi6 


:  Br2  and  (C3H5)  (C18H3302)3  :  Br6. 


The  mean  of  three  estimations  each  in  turpentine  and  aniline  were 
236  '0  and  169  '8  per  cent.,  five  estimations  in  olive  oil  (triolein) 
54  per  cent.  The  percentage  by  calculation  is  respectively  235-3, 
172,  and  54  '3. 

The  Iodine  Method.  —  This  has  been  worked  out  by  Baron  Hubl 
and  others,  but  is  not  nearly  so  expeditious  as  the  method  just 
described  ;  though,  as  before  stated,  it  has  to  a  large  extent  replaced 


§    81.  OILS   AND   FATS.  343 

it,  owing  mainly  to  the  fact  that  less  trouble  is  required,  and  the 
reactions  involved  are  less  delicate  while  equally  accurate. 

The  Standard  Iodine  Solution. — This  is  made  by  dissolving 
respectively  25  gm.  of  iodine  and  30  gm.  of  mercuric  chloride  in 
separate  portions  of  strongest  alcohol,  say  500  c.c.,  then  mixing  the 
two  liquids,  and  allowing  to  stand  for  some  hours  before  taking 
the  standard  with  thiosulphate  and  starch.  This  solution  must 
always  be  standardized  before  use. 

The  Analysis :  0'2  to  0'5  gm.  of  the  fat  or  oil  is  dissolved  in  10  c.c.  of 
purest  chloroform  in  a  well  stoppered  flask,  and  20  c.c.  of  the  iodine  solution 
added.  The  amount  must  finally  be  regulated,  so  that  after  not  less  than 
two  hours'  digestion  the  mixture  possesses  a  dark  brown  tint ;  under  any 
circumstances  it  is  necessary  to  have  a  considerable  excess  of  iodine  (at  least 
double  the  amount  absorbed  ought  to  be  present),  and  the  digestion  should 
be  from  six  to  eight  hours.  Some  KI  solution  is  then  added,  the  whole 
diluted  with  150  c.c.  of  water,  and  •£&  thiosulphate  delivered  in  till  the  colour 
is  nearly  discharged.  Starch  is  then  added,  and  the  titration  finished  in  the 
usual  way. 

The  numbers  obtained  by  Hubl  are  given  in  J.  S.  C.  I.  iii.  642. 

A  blank  experiment  should  in  every  case  be  made  side  by  side 
with  the  sample,  using  the  same  proportions  of  chloroform  and 
iodine  solution. 

Allen  states  that,  in  both  these  methods  of  titration,  the 
amount  of  halogen  taken  up  may  be  considered  as  a  measure  of 
the  unsaturated  fatty  acids  (or  their  glycerides)  present.  Thus,  the 
acids  of  the  acetic  or  stearic  series  exhibit  no  tendency  to  combine 
with  bromine  or  iodine  under  the  conditions  of  the  experiments, 
while  the  acids  of  the  acrylic  or  oleic  series  assimilate  two,  and  the 
acids  of  the  linoleic  series  four  atoms  of  the  halogen. 

"We  are  indebted  to  R.  T.  Thompson  and  H.  Ballaiityne 
(/.  S.  C.  I.  ix.  588)  for  a  very  careful  revision  of  the  constants 
required  in  the  analysis  of  Oils  and  Fats,  the  results  of  which  are 
given  in  the  following  table.  The  lards  operated  upon  were 
rendered  by  themselves  and  are  therefore  genuine.  The  fact  is 
brought  out  that  for  each  0*1  increase  in  specific  gravity,  there  is 
an  increase  of  1*3  per  cent,  iodine  absorption,  and  beef  fat  seems 
to  follow  the  same  rule.  Cotton  seed  oil  shows  only  about  half 
that  proportion. 

In  using  the  iodine  absorption  method  these  operators  found 
that  some  oils  required  fully  eight  hours  for  complete  absorption, 
and  they  recommend,  as  a  rule,  to  start  the  digestion  in  the  evening 
and  titrate  the  solutions  on  the  following  morning. 


344  VOLUMETRIC  ANALYSIS.  §    81. 

Table   of   Constants   in   the  Analysis   of   Oils. 


Nature  of  Oil  or  Fat. 

Sp.  Gr. 
at  15-5°  C. 

Sp.  Gr. 
at  99°  C. 

Iodine 
Absorptn. 

KOH 

Neutrlizd. 

Free  Acid. 

per  cent. 

per  cent. 

per  cent. 

Olive  (Gioja)  

915-6 

— 

79-0 

19-07 

9'42 

Olive   (Gioja)    after    re- 

moval of  free  acid     .  .  . 

915-2 

.  — 

79-0 

19-07 

None. 

Olive       

914-8 

— 

83-2 

18-93 

3-86 

Olive       

914-7 

— 

80-0 

— 

23-78 

Olive       

916-8 

— 

83-1 

19-00 

5-19 

Olive       ...     

916-0 

— 

81-6 

— 

19-83 

Olive  (for  dyeing) 

915'4 



78'9 

19'00 

9-67 

Olive       

914-5 



86-4 

18-90 

11-28 

Olive  (for  cooking) 

915-1 

— 

83-1 

19-20 

4-15 

Olive  (for  cooking) 

916-2 

— 

81-2 

19-21 

Not  done 

Lard  (from  omentum)  ... 

— 

859-8 

52-1 

— 

.  — 

Lard  (from  leg)       .     .  . 



860'5 

61'3 





Lard  (from  ribs)    

— 

860-6 

62-5 

— 



Beef  fat  (from  suet)     .  .  . 

— 

857-2 

34-0 

— 

— 

Beef  fat  (oleomargarine) 

— 

858-2 

46-2 

— 

— 

Pat  from  marrow  of  ox... 

— 

858-5 

45-1 

19-70 



Fat  from  bone  of  ox     ... 

— 

859-2 

47-0 

19-77 

— 

Cotton  seed    

923-6 

868-4 

110-1 

— 

— 

Cotton  seed    

922-5 

— 

106-8 

19-35 

0-27 

Linseed  (Baltic)    

934-5 



187-7 

19-28 



Linseed  (East  India)     .  .  . 

931-5 



178-8 

19-28 



Linseed  (River  Plate)  ... 

932-5 

.  . 

175-5 

19-07 

.  

Linseed  

932-5 

— 

173-5 

19-00 

0-76 

Linseed  

931-2 



168-0 

19-00 



Rape       

916-8 

— 

105-6 

17-53 

2-43 

Rape       

913-1 

— 

110-7 

17-33 

.  — 

Rape       

914-5 

— 

104-1 

17-06 

2-53 

Eape       

915-0 



104-5 

17-19 

3-10 

Eape       

914-1 

— 

100-5 

17-39 

— 

Castor  (commercial) 

967-9 

— 

83-6 

18-02 

2-16 

Castor  (commercial) 

965-3 

— 

— 

17*86 

— 

Castor  (medicinal) 

963-7 

— 

— 

17-71 

— 

Arachis  (commercial)    ... 

920-9 

— 

98-7 

19-21 

6-20 

Arachis  (French  refined) 

917-1 

— 

98-4 

18-93 

0-62 

Lard  oil  (prime)    

917-0 



76-2 

— 

— 

Southern  sperm 

880*8 



81'3 

13'25 



Arctic  sperm  (bottle-nose) 

879-9 

— 

82-1 

13-04 

— 

Whale  (crude  Norwegian) 

920-8 

— 

109-2 

— 

— 

Whale  (pale)  

919-3 

— 

110-1 

— 

— 

Seal  (Norwegian)  

925-8 

— 

152-1 

— 

-  - 

Seal  (cold  drawn,  pale)  .  .  . 

926-1 

— 

145-8 

19-28 

— 

Seal  (steamed,  pale) 

924-4 



142-2 

18-93 



Seal  (tinged)  

925-7 

— 

152-4 

— 

— 

Seal  (boiled)  ...     

923-7 

— 

142-8 

— 

— 

Menhaden      

931-1 



160-0 

18-93 



Newfoundland  cod 

924-9 

.  

160-0 



— 

Scotch  cod      

925-0 

— 

158-7 

— 

.  — 

Cod  liver  (medicinal)    .  .  . 

926-5 

— 

166-6 

18-51 

0-36 

Mineral  

873-6 

— 

12-8 

— 

— 

Mineral  

886-0 



26-1 





Rosin      

986-0 

— 

67-9 

— 

— 

§    82.  GLYCERIN.  345 

GLYCERIN    (GLYCEROL). 

C3H803  =  92. 

§  82.  UP  to  a  very  recent  time  no  satisfactory  method  of 
determining  glycerin  had  been  devised,  but  the  problem  has  now 
been  solved  in  a  tolerably  satisfactory  manner.  The  permanganate 
method  appears  to  have  been  originally  suggested  by  Wanklyn, 
improved  by  him  and  Fox,  and  further  elaborated  by  Benedikt 
and  Zsigmondy  (Cliem.  Zeit.  ix.  975).  It  depends  on  the 
saponification  of  the  fat,  and  oxidation  of  the  resultant  glycerin 
by  permanganate  in  alkaline  solution,  with  formation  of  oxalic 
acid,  carbon  dioxide,  and  water,  thus — 

C3Hs03  +  302  =  C2H2O  +  CO2  +  3H20. 

Aqueous  solutions  of  glycerin  may  of  course  be  submitted  to  the 
method  very  easily. 

The  -excess  of  permanganate  is  destroyed  by  a  sulphite,  the 
liquid  filtered  from  the  manganese  precipitate,  the  oxalic  acid  then 
precipitated  by  a  soluble  calcium  salt  in  acetic  solution,  and  the 
precipitated  calcic  oxalate,  after  ignition  to  convert  it  into  carbonate, 
titrated  with  standard  acid  in  the  usual  way,  or  the  oxalic 
precipitate  titrated  with  permanganate.  The  oxalic  solution  may  be 
titrated  direct  after  addition  of  H2S04  with  permanganate ;  but 
Allen  and  Belcher  have  found  this  method  faulty,  probably 
from  the  formation  of  a  dithionate,  due  to  the  sulphite.  On  the 
other  hand,  they  have  obtained  very  satisfactory  results  by  the 
alkalimetric  or  the  permanganate  titration,  on  known  weights  of 
pure  oxalic  acid  and  glycerin. 

These  operators  have  also  shown  that,  in  the  case  of  dealing  with 
fats,  where  it  has  been  recommended  by  Wanklyn  and  Fox  to 
use  ordinary  alcohol  as  the  solvent,  and  by  Benedikt  methyl 
alcohol,  both  these  media,  especially  ethylic  alcohol,  produce  in 
themselves  a  variable  quantity  of  oxalic  acid  when  treated  with 
alkaline  permanganate,  and  hence  vitiate  the  process.  Again,  if  it 
be  attempted  to  avoid  this  by  boiling  off  the  alcohols,  there  is 
a  danger  of  losing  glycerin.* 

Allen's  method  with  oils  and  fats  is  as  follows  : — 

10  gm.  of  the  fat  or  oil  are  placed  in  a  strong  small  bottle,  together  with 
4  gm.  of  pure  KHO  dissolved  in  25  c.c.  of  water.  A  solid  rubber  stopper  is 
then  used  to  close  the  bottle,  and  tied  down  firmly  with  wire.  It  is  then 
placed  in  boiling  water,  or  in  a  water  oven,  and  heated,  with  occasional 
shaking,  from  6  to  10  hours,  or  until  the  contents  are  homogeneous,  and  all 
oily  globules  have  disappeared.  When  saponification  is  complete,  the  bottle 
is  emptied  into  a  beaker  and  diluted  with  hot  water  which  should  give  a  clear 

*  In  dealing  with  waxes  or  similar  "bodies  including  sperm  oil,  potash,  dissolved  in 
methyl  alcohol  must  be  used  for  the  saponification,  as  it  is  almost  impossible  to  do  it 
with  aqueous  potash. 


346  VOLUMETRIC  ANALYSIS.  §    82. 

solution,  the  fatty  acids  are  then  separated  by  dilute  acid,  filtered,  and  the 
nitrate  made  up  to  a  given  volume. 

This  solution,  which  will  usually  contain  from  0'2  to  0'5  of  glycerol, 
according  to  its  origin,  is  transferred  to  a  porcelain  basin  and  diluted  with 
cold  water  to  about  400  c.c.  From  10  to  12  gm.  of  caustic  potash  should 
next  be  added,  and  then  a  saturated  aqueous  solution  of  potassic  permanganate 
until  the  liquid  is  no  longer  green  but  blue  or  blackish.  An  excess  does  no 
harm.  The  liquid  is  then  heated  and  boiled  for  about  an  hour,  when  a  strong- 
solution  of  sodic  sulphite  should  be  added  to  the  boiling  liquid  until  all 
violet  or  green  colour  is  destroyed.  The  liquid  containing  the  precipitated 
oxide  of  manganese  is  then  poured  into  a  500  c.c.  flask,  and  hot  water 
added  to  15  c.c.  above  the  mark,  the  excess  being  an  allowance  for  the 
volume  of  the  precipitate  and  for  the  increased  measure  of  the  hot  liquid. 
The  solution  is  then  passed  through  a  dry  filter,  and,  when  cool,  400  c.c.  of 
the  filtrate  should  be  measured  off,  acidified  with  acetic  acid,  and  precipitated 
with  calcic  chloride.  The  solution  is  kept  warm  for  three  hours,  or  until 
the  deposition  of  the  calcic  oxalate  is  complete,  and  is  then  filtered,  the 
precipitate  being  washed  with  hot  water.  The  precipitate  consists  mainly  of 
calcic  oxalate,  but  is  liable  to  be  contaminated  more  or  less  with  calcic 
sulphate,  silicate,  and  other  impurities,  and  hence  should  not  be  directly 
weighed.  It  may  be  ignited,  and  the  amount  of  oxalate  previously  present 
deduced  from  the  volume  of  normal  acid  neutralized  by  the  residual  calcic 
carbonate,  but  a  preferable  plan  is  to  titrate  the  oxalate  by  standard 
permanganate.  Tor  this  purpose,  the  filter  should  be  pierced  and  the 
precipitate  rinsed  into  a  porcelain  basin.  The  neck  of  the  funnel  is  then 
plugged,  and  the  filter  filled  with  dilute  sulphuric  acid.  After  standing 
for  five  or  ten  minutes  this  is  allowed  to  run  into  the  basin  and  the  filter 
washed  with  water.  Acid  is  added  to  the  contents  of  the  basin  in  quantity 
sufficient  to  bring  the  total  amount  used  to  10  c.c.  of  concentrated  acid,  the 
liquid  diluted  to  about  200  c.c.,  brought  to  a  temperature  of  about  60°  C., 
and  decinormal  permanganate  added  gradually  till  a  distinct  pink  colouration 
remains  after  stirring.  Each  c.c.  of  permanganate  used  corresponds  to  0'0045 
gm.  of  anhydrous  oxalic  acid,  or  to  0'004fc5  gm.  of  glycerin.  Operating  in  the 
way  described,  the  volume  of  permanganate  solution  required  will  generally 
range  between  70  and  100  c.c. 

Otto  Hehner  has  experimented  largely  on  the  estimation  of 
glycerol  in  soap  leys  and  crude  glycerins,  the  results  of  which  are 
given  in  J.  S.  C.  I.  viii.  4.  The  volumetric  methods  recommended 
in  preference  to  the  permanganate  are  the  oxidation  with  potassic 
bichromate  or  the  conversion  of  the  glycerol  into  triacetin. 

The  Bichromate  Method. — One  part  of  glycerol  is  completely 
converted  into  carbonic  acid  by  7 '486  parts  of  bichromate  in  the 
presence  of  sulphuric  acid.  The  solutions  required  are  :— 

Standard  Potassic  bichromate. — 74 '86  gm.  of  pure  potassic 
bichromate  is  dissolved  in  water.  150  c.c.  of  concentrated  sulphuric 
acid  added,  and  when  cold  diluted  to  a  liter.  1  c.c.  =  0 '01  gm. 
glycerol. 

A  weaker  solution  is  also  made  by  diluting  100  c.c.  of  the  strong 
solution  to  a  liter. 

These  solutions  should  be  controlled  by  a  ferrous  solution 
of  known  strength,  if  there  is  any  doubt  about  the  purity  of  the 
bichromate. 


§    82.  GLYCERIN.  347 

Solution  of  double  Iron  salt. — 240  gm.  of  ferrous  ammonium 
sulphate  is  dissolved  with  50  c.c.  of  concentrated  sulphuric  acid  to 
a  liter,  and  its  relation  to  the  standard  bichromate  must  be 
accurately  found  from  time  to  time  by  titration  with  the  latter, 
using  the  ferricyanide  indicator  (§  33,  p.  111). 

The  Analysis :  With  concentrated  or  tolerably  pure  samples  of  glycerin 
it  is  only  necessary  to  take  a  small  weighed  portion,  say  0'2  gm.  or  so,  dilute 
moderately,  add  10  or  15  c.c.  of  concentrated  sulphuric  acid  and  30  or  40  c.c. 
of  the  stronger  bichromate,  place  the  beaker  covered  with  a  watch  glass  in 
a  water  bath  and  digest  for  two  hours ;  the  excess  of  bichromate  is  then 
found  by  titration  with  the  standard  iron  solution.  The  weaker  bichromate 
is  useful  in  completing  the  titration  where  accuracy  is  required.  As  the 
stronger  bichromate  and  the  iron  solution  are  both  concentrated,  they  must 
be  used  at  a  temperature  as  near  16°  C.  as  possible.  In  the  case  of  crude 
glycerin  it  must  be  purified  from  chlorine  or  aldehyde  compounds  as 
follows  : — About  1'5  gm.  of  the  diluted  sample  is  placed  in  a  100  c.c.  flask, 
some  moist  silver  oxide  added,  and  allowed  to  stand  10  minutes.  Basic  lead 
acetate  is  then  added  in  slight  excess,  the  measure  made  up  to  100  c.c., 
filtered  through  a  dry  filter,  and  25  c.c.  or  so  digested  with  excess  of 
bichromate,  and  titrated  as  before  described. 

The  Acetin  Method. — This  method  is  due  to  Benedikt  and 
Cantor  (Monatslieft  ix.  521),  and  recommends  itself  by  its 
simplicity  and  rapidity  as  compared  with  other  methods.  Hehner 
has  pointed  out  the  precautions  necessary  to  insure  accuracy  as 
follows : — 

The  Analysis :  About  1*5  gm.  of  the  crude  glycerin  is  placed  in  a  round- 
bottomed  flask,  together  with  7  gm.  of  acetic  anhydride  and  3  gm.  of 
perfectly  anhydrous  sodic  acetate  ;  an  upright  condenser  is  attached  to  the 
flask,  and  the  contents  are  heated  to  gentle  boiling  for  one  hour  and  a  half. 
After  cooling,  50  c.c.  of  water  are  added,  and  the  mixture  heated  until  all 
triacetin  has  dissolved.  The  solution  is  then  filtered  into  a  large  flask,  the 
residue  or  filter  well  washed,  the  liquid  cooled,  some  phenolphthalein  added, 
and  the  acidity  exactly  neutralized  by  a  dilute  solution  of  caustic  soda.  The 
triacetin  is  then  saponified  by  adding  25  c.c.  of  an  approximately  10  per 
cent,  solution  of  pure  caustic  soda  standardized  on  normal  sulphuric  or 
hydrochloric  acid,  and  boiling  for  10  minutes,  taking  care  to  attach  a  reflux 
condenser  to  the  flask.  The  excess  of  alkali  is  then  titrated  back  with 
normal  acid,  each  c.c.  of  which  represents  0'0306T  gm.  of  glycerin. 

It  is  essential  that  the  processes  of  analysis  should  be  rapid  and 
continuous,  and  especially  that  the  free  acetic  acid  in  the  first  process  be 
neutralized  very  cautiously,  and  with  constant  agitation  to  avoid  the  local 
action  of  alkali. 

Weak  soap  lyes  should  be  concentrated  to  50  per  cent,  of 
glycerin  if  estimated  by  the  acetin  method ;  if  not  the  bichromate 
method  must  be  used. 

For  fats  and  soaps  about  3  gm.  should  be  saponified  with 
alcoholic  potash,  diluted  with  200  c.c.  of  water,  the  fatty  acids 
separated  and  filtered  off.  The  filtrate  and  washings  are  then 
rapidly  boiled  to  one-half  and  titrated  with  bichromate. 


3-48  VOLUMETRIC  ANALYSIS.  §    83. 

PHENOL    (CABBOLIC    ACID). 


§  83.  THE  only  method  claiming  accuracy  for  the  estimation  of 
this  substance  volumetrically  was  originated  by  Koppeschaar 
(Z.  a.  C.  xvi.  233),  and  consists  in  precipitating  the  phenol  from 
its  aqueous  or  dilute  alcoholic  solution  with  bromine  water  in  the 
form  of  tribromphenol. 

The  strength  of  the  bromine  water  was  established  by 
Koppeschaar,  by  titration  with  thiosulphate  and  potassic  iodide 
with  starch. 

Allen  modifies  the  process  as  follows  :  — 

A  certain  weight  of  the  sample  is  dissolved  in  water;  as  much  as 
corresponds  to  O'l  gm.  of  phenol  is  taken  out  and  put  into  a  stoppered  bottle 
holding  250  c.c.  Further,  to  7  c,c.  of  normal  soda  solution  (  =  0'04  gin. 
NaOH  per  c.c.)  bromine  is  gradually  added  till  a  yellow  colour  appears  and 
remains  ;  the  liquid  is  then  boiled  till  it  has  become  colourless  again.  It 
now  contains  5  molecules  of  sodic  bromide  and  1  of  sodic  bromate.  When 
completely  cooled,  it  is  put  into  the  phenol  solution,  after  which  5  c.c.  con- 
centrated hydrochloric  acid  is  at  once  added,  and  the  bottle  stoppered  and 
shaken  for  some  time.  The  reactions  are  :  — 


II.     C6H60+6Br=C6H3Br30+3HBr. 

The  bromine  set  free  in  the  first,  and  not  fixed  by  phenol  in  the  second 
reaction,  must  be  still  free,  and  is  estimated  by  adding  potassic  iodide  and 
titrating  the  iodine  liberated,  by  YTT  thiosulphate  :  — 

III.  2KI+Br2=2KBr+2l. 

IV.  I2+2Na2S203=Na2S4O6+2NaI. 

For  this  purpose  the  bottle  is  allowed  to  stand  for  15  or  20  minutes; 
a  solution  of  about  1*25  gm.  potassic  iodide  (free  from  iodate)  is  added,  the 
bottle  is  stoppered,  shaken  up,  and  allowed  to  rest.  Its  contents  are  now 
poured  into  a  beaker  ;  the  bottle  is  rinsed  out,  a  little  starch  solution  is  added, 
and  thiosulphate  is  run  in  from  a  burette  till  the  blue  colour  is  gone.  (It 
will  be  best  not  to  add  the  starch  till  the  colour  of  the  liquid  has  diminished 
to  light  yellow.)  The  calculation  is  made  as  follows  :  —  7  c.c.  of  normal  soda 
solution  neutralize  0'56  gm.  of  bromine,  all  of  which  is  liberated  by  HC1. 
O'l  gm.  phenol  would  require  0'4068  and  leave  a  surplus  of  01532  gm.  ;  the 
latter  would  liberate  enough  iodine  to  saturate  19'5  c.c.  of  TNT  thiosulphate. 
Every  c.c.  of  thiosulphate  used  over  and  above  this  indicates  0'00197  gm. 
impurities  in  O'l  gm.  of  the  sample—  that  is,  1*27  per  cent. 

If  a  number  of  estimations  have  to  be  made  at  one  time,  it 
would  seem  decidedly  preferable  to  adopt  Koppeschaar's  original 
method,  rather  than  to  prepare  special  bromine  solution  as  above. 
For  the  estimation  of  phenol  in  raw  products,  Tb'th  (Z.  a.  C. 
xxv.  160)  modifies  the  bromine  process  as  follows  :  — 

20  c.c.  of  the  impure  carbolic  acid  are  placed  in  a  beaker  with  20  c.c.  of 
caustic  potash  solution  of  T3  sp.  gr.,  well  shaken,  and  allowed  to  stand  for 
half  an  hour,  then  diluted  to  about  k  liter  with  water.  By  this  treatment 
the  foreign  impurities  are  set  free,  and  may  mostly  be  removed  by  filtration  ; 


§    84.  CAftBON   BISULPHIDE.  349 

the  filter  is  washed  with  warm  water  until  all  alkali  is  removed.  The 
filtrate  and  washings  are  acidulated  slightly  with  HC1,  and  diluted  to  3  liters. 
50  c.c.  are  then  mixed  with  150  c.c.  of  standard  bromine  solution,  and  then 
5  c.c.  concentrated  HC1.  After  twenty  minutes,  with  frequent  shaking, 
10  c.c.  of  iodide  solution  are  added,  mixed,  and  allowed  to  rest  three  to  five 
minutes,  then  starch,  and  the  titration  with  thiosulphate  carried  out  as  usual. 
Example  :  20  c.c.  raw  carbolic  oil  were  treated  as  above  described.  50  c.c. 
of  the  solution,  with  150  c.c.  bromine  solution  (made  by  dissolving  2'04  gm. 
sodic  bromate  and  6'959  gm.  sodic  bromide  to  the  liter),  then  5  c.c.  of  HC1, 
required  lY'8  c.c.  of  thiosulphate  for  titration.  The  150  c.c.  bromide 
=0'237  gm.  Br.  The  17'8  c.c.  thiosulphate  required  for  residual  titration 
=  0'052  gm.  Br,  leaving  0*185  gm.  Br  for  combination  with  the  phenol. 
According  to  the  equation  — 


One  niol.  phenol  =3  mol.  Br,  hence  the  percentage  of  phenol  was  10'86. 

Kleinert  (Z.  a.  C.  xxxiii.  1)  suggests,  and  his  experiments 
appear  to  prove,  that  in  titrating  acid  creosote  oil  by  Koppeschaar'  s 
method  for  phenol,  a  serious  error  occurs  in  virtue  of  such  oil 
containing  substances  of  higher  boiling  point  than  phenol,  which 
are  soluble  in  water,  and  behave  with  bromine  in  the  same  manner 
as  true  phenol. 


CARBON    BISULPHIDE    AND    THIOCARBONATES. 


§  84.  FOR  the  purpose  of  estimating  carbon  disulphide  in  the 
air  of  soils,  gases,  or  in  thiocarbonates,  Gas  tine  has  devised  the 
following  process  (Compt.  Rend,  xcviii.  1588)  :  — 

The  gas  or  vapour  to  be  tested  is  carefully  dried,  and  then  passed  through 
a  concentrated  solution  of  recently  fused  potassic  hydroxide  in  absolute 
alcohol.  The  presence  of  even  traces  of  water  seriously  diminishes  the 
delicacy  of  the  reaction.  The  alcoholic  solution  is  afterwards  neutralized 
with  acetic  acid,  diluted  with  water,  and  tested  for  xanthic  acid  by  adding 
copper  sulphate. 

In  order  to  determine  the  distribution  of  carbon  bisulphide  introduced 
into  the  soil,  250  c.c.  of  the  air  in  the  soil  is  drawn  by  means  of  an  aspirator 
through  sulphuric  acid,  and  then  through  bulbs  containing  the  alcoholic 
potash.  For  quantitative  determinations,  a  larger  quantity  of  air  must  be 
used,  and  the  xanthic  acid  formed  is  estimated  by  means  of  the  reaction 
2C3H6OS2+I2=2C3H5OS2+2HI.  The  alkaline  solution  is  slightly  acidified 
with  acetic  acid,  mixed  with  excess  of  sodic  bicarbonate,  and  titrated  in  the 
usual  way  with  a  solution  of  iodine  containing  T68  gm.  per  liter,  1  c.c.  of 
which  is  equivalent  to  1  m.gm.  of  carbon  bisulphide. 

To  apply  this  method  to  thiocarbonates,  about  1  gm.  of  the  substance, 
together  with  about  10  c.c.  of  water,  is  introduced  into  a  small  flask  and 
decomposed  by  a  solution  of  zinc  or  copper  sulphate,  the  flask  being  heated 
on  a  water  bath,  and  the  evolved  carbon  bisulphide  passed,  first  through 
sulphuric  acid,  and  then  into  alcoholic  potash.  In  the  case  of  gaseous 
mixtures  of  carbon  bisulphide,  nitrogen,  hydrogen  sulphide,  carbonic 
anhydride,  carbonic  oxide,  and  water-vapour,  the  gas  is  passed  through 
a  strong  aqueous  solution  of  potash,  then  into  sulphuric  acid,  and  finally  into 


350  VOLUMETRIC   ANALYSIS.  §    85. 

alcoholic  potash.  The  thiocarbonate  formed  in  the  first  flask  is  decomposed 
by  treatment  with  copper  or  zinc  sulphate  as  above,  and  the  xanthic  acid 
obtained  is  added  to  that  formed  in  the  third  flask,  and  the  whole  titrated 
with  iodine. 

Another  method  available  for  technical  purposes,  such  as  the 
comparative  estimation  of  CS2  in  coal  gas,  or  in  comparing  samples 
of  thioearbonates,  is  as  follows  : — 

The  liquid,  or  other  substance,  containing  the  disulphide,  is  added  to 
strong  alcoholic  potash  or  gas  containing  the  CS2,  is  passed  slowly  through 
the  alkaline  absorbent.  The  disulphide  unites  with  the  potassic  ethylate  to 
form  potassic  xanthate.  The  liquid  is  neutralized  with  acetic  acid  and  the 
xanthate  is  then  estimated  by  titrating  with  a  standard  solution  of  cupric 
sulphate  (12*47  gm.  per  liter),  until  an  excess  of  copper  is  found  by  potassic 
ferrocyanide  used  as  an  external  indicator.  Each  c.c.  of  copper  solution 
represents  0'0076  gm.  CS2. 


MOLYBDENUM  AND  TUNGSTEN. 

Mo  =  95-8.     W=184. 

§  85.  VOLUMETRIC  methods  are  probably  of  very  limited  use  in 
the  case  of  these  substances,  but  cases  may  arise  in  which  their 
estimation  is  more  simply  accomplished  by  volumetric  than  by 
gravimetric  means. 

Von  d.  Pf  or  d  ten  (0.  N.I.  18)  gives  the  following  processes  : — 

The  solution  of  the  salt  is  mixed,  for  molybdenum,  with  50—60  c.c.,  and 
for  tungsten  with  70 — 80  c.c.  of  HC1  of  27  per  cent.  There  are  then  added 
for  molybdenum,  8 — 10  gm.,  and  for  tungsten  14 — 15  gm.  zinc  in  the  form 
of  rods,  and  in  as  large  pieces  as  possible.  The  solution  may  contain  03  gm. 
molybdic  oxide,  or  O'l  gm.  of  tungstic  oxide ;  in  the  latter  case,  the  solution 
is  previously  heated  on  the  water  bath,  and  the  HC1  and  zinc  are  then 
added ;  the  deposition  of  tungstic  oxide  in  a  solid  state  is  thus  avoided. 
Towards  the  end  of  the  reduction,  a  little  heat  may  sometimes  be  applied  to  the 
molybdenum  solution  also  with  advantage.  When  the  molybdenum  solution 
has  become  yellow,  and  that  of  tungsten  red,  the  flask  is  cooled — in  the  case 
of  tungsten  with  especial  care.  The  remainder  of  the  procedure  is  different. 
The  molybdenum  solution  is  poured  into  a  porcelain  capsule  containing 
40  c.c.  dilute  sulphuric  acid,  and  20  c.c.  of  manganous  sulphate  solution  free 
from  ferrous  salt,  and  containing  200  gm.  per  liter.  An  equal  volume  of 
water  is  added,  and  a  dilute  solution  of  standard  permanganate  is  run  in. 
The  results  are  accurate  : 

1  c.c.  KMnO4= 0-000752185  O=0'0045131lMoO3. 

The  reduced  tungsten  solution  is  rinsed  quickly  into  a  capsule  in  which 
there  is  an  excess  of  permanganate,  70—100  c.c.  dilute  sulphuric  acid,  40  c.c. 
manganous  sulphate  solution,  but  otherwise  no  water.  Not  until  the  flask 
has  been  rinsed  out  is  the  liquid  diluted  to  1  liter.  In  presence  of  such 
large  quantities  of  HC1  the  manganous  sulphate  exerts  its  power  of 
transferring  oxygen  only  in  concentrated  solutions.  Quick  working  is 
essential.  An  excess  of  ferrous  sulphate  is  now  run  in,  and'  the  solution  is 
finally  titrated  with  permanganate. 


§    85.  MOLYBDENUM   AND   LEAD.  351 

Schindler's  Method  for  Molybdenum  and  Lead  (Z.  a.  C. 
xxvii.  137). — This  process  has  already  been  referred  to  under 
Phosphoric  acid  (§  69).  It  was  originally  designed  for  the 
estimation  of  molybdenum  and  incidentally  applied  to  lead.  It  is 
based  on  the  fact  that  lead  acetate,  when  added  to  a  hot  solution 
of  ammonic  molybdate,  gives  a  precipitate  of  PbMoO4,  which  is 
insoluble  in  acetic  acid.  Any  excess  of  the  molybdate  solution 
shows  a  colour  varying  from  yellow  to  blood  red  with  a  freshly 
prepared  solution  of  tannin  (1 — 300)  as  indicator,  according  to  the 
amount  present. 

The  method  requires  the  following  solutions  : — 

Standard  Lead  acetate. — 50  gm.  of  acetate  is  dissolved  in  a  liter 
of  water  with  10  c.c.  of  acetic  acid;  it  is  then  to  be  standardized 
with  a  known  weight  of  pure  ammonic  molybdate. 

Standard  Ammonic  molybdate. — This  may  be  made  with  the 
ordinary  commercial  salt  by  dissolving  about  20  gm.  in  700 — 800 
c.c.  of  water,  adding  a  little  ammonia  to  render  it  clear.  It  is 
standardized  by  the  following  method,  so  that  1  c.c.  shall  equal 
1  c.c.  of  lead  solution. 

The  Analysis :  To  50  c.c.  of  the  molybdenum  solution  faintly  acidified 
with  acetic  acid,  about  300  c.c.  of  boiling  water  is  added,  and  the  standard  lead 
solution  run  in  until  the  whole  of  the  molybdic  acid  is  precipitated,  and  a 
slight  excess  of  lead  occurs,  which  may  be  known  by  removing  a  drop  from  the 
clear  liquid,  and  bringing  it  in  contact  with  a  drop  of  the  tannin  indicator 
on  a  porcelain  tile;  if  an  excess  of  lead  has  been  used  no  colour  occurs. 
Standard  molybdic  solution  is  then  cautiously  added,  until  by  similar  testing 
a  distinct  orange  colour  appears.  The  volume  of  the  latter  is  deducted  from 
the  volume  of  lead  solution  originally  used  and  the  remainder  calculated  to 
molybdic  acid,  207Pb=144MoO3. 

The  method  is  capable  of  giving  very  good  results,  and  is 
applicable  to  the  analysis  of  lead  compounds,  such  as  white  lead, 
by  dissolving  in  nitric  acid,  neutralizing  with  ammonia,  then 
acidifying  with  acetic  acid  before  titrating. 

The  accuracy  of  the  method  depends  on  a  correct  molybdic 
standard ;  the  pure  ammonium  salt  has  the  formula  (NH4)6Mo7024 
+  4H20,  and  should  when  ignited  in  a  platinum  crucible  to 
a  constant  weight  give  81 '55  per  cent.  MoO3. 


352  VOLUMETFJC  ANALYSIS.  8    86. 


PAET  VI. 

SPECIAL  APPLICATIONS  OF  THE  VOLUMETRIC 

SYSTEM    TO    THE    ANALYSIS    OF    URINE,    POTAELE 

WATERS,  SEWAGE,  ETC. 

ANALYSIS    OF    URINE. 

§  86.  THE  complete  and  accurate  determination  of  the  normal 
and  abnormal  constituents  of  urine  presents  more  than  ordinary 
difficulty  to  even  experienced  chemists,  and  is  a  hopeless  task  in 
the  hands  of  any  other  than  such.  Fortunately,  however,  the 
most  important  matters,  such  as  urea,  sugar,  phosphates,  sulphates, 
and  chlorides,  can  all  be  determined  volumetrically  with  accuracy 
by  ordinary  operators,  or  by  medical  men  who  cannot  devote 
much  time  to  practical  chemistry.  The  researches  of  Liebig, 
Neubauer,  Bence  Jones,  Vogel,  Beale,  Hassall,  Pavy, 
and  others,  during  the  last  few  years,  have  resulted  in  a  truer 
knowledge  of  this  important  secretion;  and  to  the  two  first 
mentioned  chemists  we  are  mainly  indebted  for  the  simplest 
and  most  accurate  methods  of  estimating  its  constituents.  With 
the  relation  which  the  proportion  of  these  constituents  bear 
to  health  or  disease  the  present  treatise  has  nothing  to  do,  its 
aim  being  simply  to  point  out  the  readiest  and  most  useful 
methods  of  determining  them  quantitatively.  Their  pathological 
importance  is  very  fully  treated  by  some  of  the  authorities  just 
mentioned,  among  the  works  of  which  Neubauer  and  Vo gel's 
Analyse  des  Hams,  Beale 's  Urine,  Urinary  Deposits,  and  Calculi, 
and  Menu's  Traite  de  Cliimie  Medicate,  are  most  prominent  and 
exhaustive ;  and  we  now  have  the  collected  experience  of  all 
the  best  authorities  in  the  world  in  The  Pathological  Handbook 
of  Drs.  Lander  Brunton,  Klein,  Foster,  and  Burdon 
Sanderson  (Churchill). 

The  gram  system  of  weights  and  measures  will  be  adopted 
throughout  this  section,  while  those  who  desire  to  use  the  grain 
system  will  have  no  difficulty  in  working,  when  once  the  simple 
relation  between  them  is  understood*  (see  §  9,  p.  22).  The  question 
of  weights  and  measures  is,  however,  of  very  little  consequence,  if 
the  analyst  considers  that  he  is  dealing  with  relative  parts  or  pro- 

*  In  a  word,  wherever  c.c.  occurs,  dm.  may  be  substituted;  and  in  case  of  usin.? 
grains  for  grams,  move  the  decimal  point  one  place  to  the  right ;  thus  7'0  grams  would 
be  changed  to  70  grains.  Of  course  it  is  understood  that  where  grams  are  taken  c.c. 
must  be  measured,  and  with  grains  dm.,  the  standard  solution  being  the  same  for  both 
systems. 


§  86.  URINE.  353 

portions  only  ;  and  as  urine  is  generally  described  as  containing  so 
many  parts  of  urea,  chlorides,  or  phosphates,  per  1000,  the  absolute 
weight  may  be  left  out  of  the  question.  The  grain  system  is  more 
readily  calculated  into  English  ounces  and  pints,  and  therefore  is 
generally  more  familiar  to  the  medical  profession  of  this  country. 

One  thing,  however,  is  necessary  as  a  preliminary  to  the  exami- 
nation of  urine,  and  which  has  not  generally  been  sufficiently 
considered ;  that  is  to  say,  the  relation  between  the  quantity  of 
secretion  passed  in  a  given  time,  and  the  amount  of  solid  matters 
found  in  it  by  analysis.  In  a  medical  point  of  view  it  is  a  mere 
waste  of  time,  generally  speaking,  to  estimate  the  constituents  in 
half-a-pint  or  so  of  urine  passed  at  any  particular  hour  of  the  day 
or  night,  without  ascertaining  the  relation  which  that  quantity, 
with  its  constituents,  bears  to  the  whole  quantity  passed  during, 
say,  24  hours ;  and  this  is  the  more  necessary,  as  the  amount  of 
fluid  secreted  varies  very  considerably  in  healthy  persons ;  besides 
this,  the  analyst  should  register  the  colour,  peculiarity  of  smell  (if 
any),  consistence,  presence  or  absence  of  a  deposit  (if  the  former, 
it  should  be  collected  for  separate  analysis,  filtered  urine  only  being 
used  in  such  cases  for  examination),  and  lastly  its  reaction  to  litmus 
should  be  observed. 


1.     Specific    Gravity. 

This  may  be  taken  by  measuring  10  c.c.  with  an  accurate  pipette 
into  a  tared  beaker  or  flask.  The  observed  weight  say  is  10*265 
gm. ;  therefore  1026*5  will  be  the  specific  gravity,  water  being  1000. 
Where  an  accurate  balance,  pipette,  or  weights  are  not  at  hand, 
a  good  urinometer  may  be  used.  These  instruments  are  now  to  be 
had  with  enclosed  thermometer  and  of  accurate  graduation. 


2.      Estimation    of   Chlorides    (calculated    as    Sodic    Chloride). 

This  may  be  done  in  several  ways,  and  I  have  placed  the 
methods  in  the  order  in  which  I  consider  they  ought  to  be  ranked 
as  regards  accuracy.  Liebig's  method  is  by  far  the  simplest,  but 
the  end-point  is  generally  so  obscure  that  the  liability  to  error  is 
very  great.  Mohr's  method  I  have  modified  by  the  use  of 
ammonic  in  place  of  potassic  nitrate,  owing  to  the  solvent  effect 
which  the  latter  has  been  found  to  produce  on  silver  chromate. 
By  ignition  the  ammonia  salt  is  destroyed. 

(a)  By  Silver  Nitrate  (Mohr). — 10  c.c.  of  the  urine  are 
measured  into  a  thin  porcelain  capsule,  and  1  gm.  of  pure  ammonic 
nitrate  in  powder  added ;  the  whole  is  then  evaporated  to  dryness, 
and  gradually  heated  over  a  small  spirit  lamp  to  low  redness  till 
all  vapours  are  dissipated  and  the  residue  becomes  white;  it  is 
then  dissolved  in  a  small  quantity  of  water,  and  the  carbonates 

A   A 


354  VOLUMETRIC   ANALYSIS.  §    86. 

produced  by  the  combustion  of  the  organic  matter  neutralized  by 
dilute  acetic  acid ;  a  few  grains  of  pure  calcic  carbonate  to  remove 
all  free  acid  are  then  added,  and  one  'or  two  drops  of  solution  of 
potassic  chromate. 

The  mixture  is  then  titrated  with  -^  silver,  as  in  §  37.2  (&). 

Each  c.c.  of  silver  solution  represents  0'005837  gm.  of  salt, 
consequently  if  12*5  c.c.  have  been  used,  the  weight  of  salt  in  the 
10  c.c.  of  urine  is  0*07296  gm.,  and  as  10  c.c.  only  were  taken, 
the  weight  multiplied  by  10,  or  what  amounts  to  the  same  thing, 
the  decimal  point  moved  one  place  to  the  right,  gives  7 '296  gm. 
of  salt  for  1000  of  urine. 

If  5*9  c.c.  of  the  urine  are  taken  for  titration,  the  number  of  c.c.  of  ^V 
silver  used  will  represent  the  number  of  parts  of  salt  in  1000  parts  of  urine. 

Pibram  (Vierteljdhrsh,  f.  prad.  Heilk,  cvi.  101)  obviates  the 
necessity  for  evaporating  the  urine  with  a  nitrate  previous  to 
titration  by  heating  the  urine  with  permanganate.  10  c.c.  of  urine 
are  mixed  with  about  5  c.c.  of  —^  permanganate,  and  40  c.c.  of 
water,  then  brought  nearly  to  boiling;  by  this  means  a  brown 
flocculent  precipitate  is  produced,  consisting  of  organic  matter  and 
manganous  salt,  which  is  filtered  away,  leaving  the  clear  liquor 
colourless,  so  that  an  excess  of  permanganate  shows  the  rose  tint 
at  once.  Enough  permanganate  must  be  used  to  give  this  tint, 
which  is  then  removed  by  a  drop  or  two  of  dilute  oxalic  acid 
solution,  a  little  calcic  carbonate  added,  and  the  fluid  titrated  with 
~Q  silver  solution  and  chromate  as  before  described.  This  method 
gives  very  good  results  with  normal  urines. 

(b)  By  Volhard's  Method. — This  is  a  direct  estimation  of  Cl 
by  excess  of  silver  and  the  excess  found  by  ammonic  sulphocyanate 
(§  39),  which  gives  very  good  results  in  the  absence  of  much 
organic  matter,  and  is  carried  out  as  follows  : — 

10  c.c.  of  urine  are  placed  in  a  100  c.c.  flask  and  diluted  to  about  60  c.c. 
2  c.c.  of  pure  nitric  acid  and  15  c.c.  of  standard  silver  solution  (1  c.c.  =  0'01 
gm.  NaCl)  are  then  added ;  the  closed  flask  is  well  shaken,  and  the  measure 
made  up  to  100  c.c.  with  distilled  water. 

The  mixture  is  then  passed  through  a  dry  filter,  and  about  70  or  80  c.c.  of 
the  clear  fluid  titrated  with  standard  ammonic  sulphocyanate  for  the  excess 
of  silver,  using  the  ferric  indicator  described  on  page  127.  The  relative 
strength  of  the  silver  and  sulphocyanate  being  known,  the  measure  of  the 
former  required  to  combine  with  the  chlorine  in  the  7  or  8  c.c.  of  urine  is 
found  and  calculated  into  NaCl. 

Arnold  (F finger's  Arcliiv.  xxxv.  541)  carries  out  this  process 
as  follows : — 

10  c.c.  of  urine  are  mixed  with  10  to  20  drops  of  nitric  acid  sp.  gr.  1*2, 
2  c.c.  of  ferric  indicator,  and  10  to  15  drops  of  solution  of  permanganate  to 
oxidize  organic  matter.  The  liquid  is  then  titrated  according  toVolhard's 
directions. 


§  86.  URINE.  355 

Another  variation  of  Molir's  method  is  proposed  by  Zuelzer 
(Bericlite,  xviii.  320). 

10  c.c.  of  urine  are  acidulated  with  nitric  acid,  and  precipitated  with  silver 
nitrate;  the  silver  chloride  is  filtered  off  and  washed,  then  dissolved  in 
ammonia :  from  this  solution  the  silver  is  precipitated  with  fresh  NH4S. 
The  excess  of  sulphide  is  then  removed  by  cadmic  nitrate,  the  liquid  diluted 
to  a  definite  volume,  and  an  aliquot  part  filtered  off,  acidulated  with  nitric 
acid,  neutralized  with  calcic  carbonate,  then  titrated  with  T^  silver  and 
chromate.  This  method  is  cumbrous,  and,  if  the  reagents  are  not  extremely 
pure,  liable  to  great  inaccuracy. 

(c)  By  Mercuric  Nitrate  (Liebig). — The  principle  of  this 
method  is  as  follows  : — If  a  solution  of  mercuric  nitrate,  free  from 
any  excess  of  acid,  is  added  to  a  solution  of  urea,  a  white  gelatinous 
precipitate  is  produced,  containing  urea  and  mercuric  oxide  in  the 
proportions  of  1  eq.  of  the  former  to  4  eq.  of  the  latter  (4HgO  +  Ur). 
When  sodic  chloride,  however,  is  present  in  the  solution,  this 
precipitate  does  not  occur  until  all  the  sodic  chloride  is  converted 
by  double  decomposition  into  mercuric  chloride  (sublimate)  and 
sodic  nitrate,  the  solution  remaining  clear ;  if  the  exact  point  be 
overstepped,  the  excess  of  mercury  immediately  produces  the  pre- 
cipitate above  described,  so  that  the  urea  present  acts  as  an  indicator 
of  the  end  of  the  process.  It  is  therefore  possible  to  ascertain  the 
proportion  of  chlorides  in  any  given  sample  of  urine  by  this  method, 
if  the  strength  of  the  mercurial  solution  is  known,  since  1  eq.  of 
mercuric  oxide  converts  1  eq.  of  sodic  chloride  into  1  eq.  each  of 
corrosive  sublimate  and  sodic  nitrate. 

Standard  Solution  of  Mercuric  nitrate. — It  is  of  great  im- 
portance that  the  solution  be  pure,  for  if  the  mercury  from  which 
it  is  made  be  contaminated  with  traces  of  other  metals,  such  as 
bismuth,  silver,  or  lead,  they  will  produce  a  cloudiness  in  the 
liquid  while  under  titration,  which  may  possibly  obscure  the  exact 
ending  of  the  reaction;  therefore  18 '42  gm.  of  the  purest  precipi- 
tated mercuric  oxide  are  put  into  a  beaker,  with  a  sufficiency  of 
pure  nitric  acid  of  about  1*20  spec.  grav.  to  dissolve  it  by  the 
aid  of  a  gentle  heat ;  the  clear  solution  so  obtained  is  evaporated 
on  the  water  bath  to  remove  any  excess  of  free  acid.  When  the 
liquid  is  dense  and  sirupy  in  consistence,  it  may  be  transferred  to 
the  graduated  cylinder  or  flask  and  diluted  to  a  liter.  1  c.c.  of  the 
solution  so  prepared  is  equal  to  0*01  gm.  of  sodic  chloride,  or 
0-006059  gm.  of  chlorine. 

If  pure  mercuric  oxide  is  not  at  hand,  the  solution  is  best  made  by  weighing 
25  gm.  of  mercuric  chloride,  which  is  dissolved  in  about  a  liter  of  water  and 
the  oxide  precipitated  with  a  slight  excess  of  caustic  potash  or  soda.  The 
precipitate  of  yellow  oxide  is  allowed  to  settle  clear  and  the  liquor  decanted. 
It  is  repeatedly  washed  in  this  manner  with  warm  distilled  water  until  the 
washings  show  no  amount  of  alkali  or  alkaline  chloride;  the  precipitate  is 
then  dissolved  in  the  smallest  quantity  of  pure  nitric  acid,  and  diluted  to 
about  950  c.c.  If  any  great  excess  of  nitric  acid  is  present,  it  may  be 
cautiously  neutralized  by  pure  sodic  hydrate  or  carbonate. 

A  A  2 


356  VOLUMETRIC   ANALYSIS.  §    86. 

Verification  of  the  Mercuric  Solution. — This  is  carried  out  by 
the  help  of  the  following  solutions  : — 

Pure  Sodic  chloride. — 20  gm.  per  liter. 

Solution  of  Urea. — 4  gm.  of  pure  urea  in  100  c.c. 

Solution  of  pure  Sodic  sulphate. — Saturated  at  ordinary  tem- 
peratures. This  is  used  to  regulate  the  action  of  the  free  acid 
which  is  liberated  in  the  reaction.  In  the  case  of  natural  urine  it 
is  not  necessary. 

Process  of  Titration:  10  c.c.  of  the  standard  sodic  chloride  (  =  0'2  gm. 
NaCl)  are  placed  in  a  small  beaker,  together  with  3  c.c.  of  the  urea  solution, 
and  5  c.c.  of  sodic  sulphate.  The  mercuric  solution  is  then  delivered  in  from 
the  burette,  with  constant  stirring,  until  a  decided  permanent  white  pre- 
cipitate is  seen  to  form.  A  mere  opalescence  may  occur  even  at  the  beginning, 
arising  from  slight  impurities  in  the  mercury,  but  this  may  be  disregarded. 
If  the  mercuric  solution  has  been  made  from  weighed  pure  oxide,  exactly  20 
c.c.  should  be  required ;  if,  on  the  contrary,  it  has  been  made  from  the  fresh 
unweighed  oxide,  somewhat  less  than  20  c.c.  should  be  required.  Say  that 
18'5  c.c.  have  been  found  to  give  the  necessary  reaction,  then  the  solution 
must  be  diluted  with  distilled  water  in  the  proportion  of  1'5  c.c.  to  every 
18'5,  or  925  c.c.  made  up  to  a  liter. 

It  may  happen  that  the  solution,  when  made  from  weighed  dry 
mercuric  oxide,  is  not  correct,  owing  to  the  difficulty  of  obtaining 
perfectly  pure  material ;  in  such  case  a  factor  must  be  used  to  bring 
the  volume  used  to  the  correct  standard. 

(cC)  Baryta  Solution  for  removing-  Phosphoric  and  Sulphuric 
Acids. — Before  urine  can  be  submitted  to  titration  by  the  mercurial 
solution,  it  is  necessary  to  remove  the  phosphoric  acid,  and  the 
proper  agent  for  this  purpose  is  a  mixture  composed  of  1  volume 
of  cold  saturated  solution  of  pure  baric  nitrate  and  2  volumes  ditto 
baric  hydrate ;  the  same  agent  is  used  previous  to  the  estimation  of 
urea,  and  may  be  simply  designated  Baryta  Solution. 

The  Analysis :  40  c.c.  of  the  clear  urine  are  mixed  with  20  c.c.  of  baryta 
solution,  and  the  thick  mixture  poured  upon  a  small  dry  filter;  when 
sufficient  clear  liquid  has  passed  through,  15  c.c.  (=10  c.c.  of  urine)  are 
taken  with  a  pipette  and  just  neutralized,  if  necessary,  with  a  drop  or  two  of 
nitric  acid.  If  not  alkaline,  the  probability  is  that  sufficient  baryta  solution 
has  not  been  added  to  precipitate  all  the  phosphoric  and  sulphuric  acids. 
This  may  be  known  by  adding  a  drop  or  so  of  the  baryta  solution  to  the 
filtrate ;  if  any  precipitate  is  produced,  it  will  be  necessary  to  mix  a  fresh 
quantity  of  urine  with  three-fourths  or  an  equal  quantity  of  baryta,  in  which 
case  17i  or  20  c.c.  must  be  taken  to  represent  10  c.c.  of  urine;  the  excess  in 
either  case  of  baryta  must  be  cautiously  neutralized  with  nitric  acid. 

The  vessel  containing  the  fluid  is  then  brought  under  a  Mohr's  burette 
containing  the  mercurial  solution,  and  small  portions  delivered  in  with 
stirring,  until  a  distinct  permanent  precipitate  is  produced.  The  volume  of 
solution  used  is  then  read  off  and  calculated  for  1000  parts  of  urine. 

Example:  15  c.c.  of  the  liquid  prepared  with  a  sample  of  urine,  as 
described  above  (  =  10  c.c.  of  urine),  required  6'2  c.c.  of  mercurial  solution: 
the  quantity  of  salt  present  was  therefore  0'062  gm.,  or  6'2  parts  in  1000 
parts  of  urine. 


§  86.  URINE.  357 

3.     Estimation   of   TJrea    (Lie  big;). 

The  combination  between  urea  and  mercuric  oxide  in  neutral  or 
alkaline  solutions  has  been  alluded  to  in  the  foregoing  article  on 
chlorides ;  it  will  therefore  probably  be  only  necessary  to  say  that 
the  determination  of  urea  in  urine  is  based  on  that  reaction ;  and 
as  the  precipitate  so  produced  is  insoluble  in  water  or  weak  alkaline 
solutions,  it  is  only  necessary  to  prepare  a  standard  solution  of 
mercury  of  convenient  strength,  and  to  find  an  indicator  by  which 
to  detect  the  point  when  all  the  urea  has  entered  into  combination 
with  the  mercury,  and  the  latter  slightly  predominates.  This 
indicator  is  sodic  carbonate.  Liebig's  instructions  are,  that  when 
in  the  course  of  adding  the  mercurial  solution  from  the  burette  to 
the  urine,  a  drop  of  the  mixture  is  taken  from  time  to  time  and 
brought  in  contact  with  a  few  drops  of  solution  of  sodic  carbonate 
on  a  glass  plate  or  in  a  watch-glass,  no  change  of  colour  is 
produced  at  the  point  of  contact  until  the  free  urea  is  all  removed ; 
when  this  is  the  case,  and  the  mercury  is  slightly  in  excess,  a  yellow 
colour  is  produced,  owing  to  the  formation  of  hydrated  mercuric 
oxide. 

The  compound  of  urea  and  mercury  consists,  according  to 
Liebig's  analysis,  of  1  eq.  of  the  former  to  4  eq.  of  the  latter ; 
that  is  to  say,  if  the  nitric  acid  set  free  by  the  mixture  is 
neutralized  from  time  to  time  with  sodic  carbonate  or  other  suitable 
alkali.  If  this  be  not  done,  the  precipitate  first  formed  alters 
in  character,  and  eventually  consists  only  of  3  eq.  of  mercury 
with  1  of  urea.  In  order  to  produce  the  yellow  colour  with 
sodic  carbonate,  there  must  be  an  excess  of  mercurial  solution. 
Theoretically,  100  parts  of  urea  should  require  720  parts  of 
mercuric  oxide;  but  practically,  772  parts  of  the  latter  are 
necessary  to  remove  all  the  urea,  and  at  the  same  time  show 
the  yellow  colour  with  alkali;  consequently  the  solution  of 
mercuric  nitrate  must  be  of  empirical  strength,  in  order  to  give 
accurate  results. 

Preparation  of  the  Mercuric  Solution. — 77*2  gill,  of  red  mercuric 
oxide,  or  71 '5  gm.  of  the  metal  itself,  are  treated  with  nitric  acid, 
as  described  in  the  previous  article  on  chlorides,  and  in  either  case 
diluted  to  1  liter :  1  c.c.  of  the  solution  is  then  equal  to  O'Ol  gm. 
of  urea.  (The  extreme  care  required  to  remove  traces  of  foreign 
metals  from  the  mercury  is  not  so  necessary  here  as  in  the  foregoing 
instance,  but  no  large  amount  of  free  acid  must  be  present.) 
Dragendorff  prefers  to  use  mercuric  chloride  in  the  preparation 
of  the  standard  solution,  by  weighing  9 6 '855  gm.  of  the  pure  salt, 
which  is  dissolved  in  water,  then  precipitated  with  dilute  caustic 
soda,  the  precipitate  well  washed  by  decantation  until  free  from 
chlorine,  then  dissolved  in  a  slight  excess  of  nitric  acid,  and  the 
solution  diluted  to  1  liter. 


358  VOLUMETRIC   ANALYSIS.  §    86. 

The  Analysis :  Two  volumes  of  the  urine  are  mixed  with  one  of  baryta 
solution  as  before  described  in  the  case  of  chlorides  (reserving  the  precipitate 
for  the  determination  of  phosphoric  acid,  if  necessary),  and  15  c.c.  (  =  10  c.c. 
of  urine)  taken  in  a  small  beaker  for  titration;  it  is  brought  under  the 
burette  containing  the  mercurial  solution  (without  neutralizing  the  excess 
of  baryta,  as  in  the  case  of  chlorides),  and  the  solution  added  in  small 
quantities' so  long  as  a  distinct  precipitate  is  seen  to  form.  A  plate  of  glass 
laid  over  dark  paper  is  previously  sprinkled  with  a  few  drops  of  solution  of 
sodic  carbonate,  and  a  drop  of  the  mixture  must  be  brought  from  time  to 
time,  by  means  of  a  small  glass  rod,  in  contact  with  the  soda.  So  long  as  the 
colour  remains  white,  free  urea  is  present  in  the  mixture ;  when  the  yellow 
colour  is  distinctly  apparent,  the  addition  of  mercury  is  discontinued,  and 
the  quantity  used  calculated  for  the  amount  of  urea.  _  It  is  always  advisable 
to  repeat  the  analysis,  taking  the  first  titration  as  a  guide  for  a  more  accurate 
estimation  by  the  second. 

Example :  15  c.c.  of  urine  deprived  of  phosphates  (  =  10  c.c.  of  the  original 
urine)  were  titrated  as  described,  and  required  17'6  c.c.  of  mercurial  solution; 
consequently  there  was  0'176  gm.  of  urea  present  in  the  10  c.c.,  or  17'6  parts 
in  the  1000  of  urine. 

The  experiments  of  Rautenberg  (Ann.  d.  Cliem.  u.  Pliarm. 
cxxxiii.  55)  and  Pfliiger  (Z.  a.  G.  xix.  375)  show,  however,  that 
the  method,  as  devised  by  Liebig,  is  open  to  serious  errors,  due  to 
the  uncertainty  in  the  point  of  neutralization. 

Pfl tiger's  researches  are  very  complete,  and  lead  to  the  follow- 
ing modification  of  the  process. 

A  solution  of  pure  urea  is  prepared  containing  2  gm.  in  100  c.c. 
10  c.c.  of  this  solution  is  placed  in  a  beaker,  and  20  c.c.  of  the 
mercury  solution  ran  into  it  in  a  continuous  stream ;  the  mixture  is 
then  immediately  brought  under  a  burette  containing  normal  sodic 
carbonate,  and  this  solution  is  added  with  constant  agitation  until 
a  permanent  yellow  colour  appears.  The  volume  of  soda  solution 
so  used  is  noted  as  that  which  is  necessary  to  neutralize  the  acidity 
produced  by  20  c.c.  of  the  mercury  solution  in  the  presence  of  urea. 
Pfliiger  found  that  by  titrating  10  c.c.  of  the  urea  solution  by 
small  additions  of  the  mercury,  and  occasional  neutralization,  the 
end  of  the  reaction  occurred  generally  at  from  17 '2  to  17 '8  c.c.  of 
mercury ;  but  when  he  ran  in  boldly  19 '7  c.c.  of  mercury,  followed 
immediately  by  normal  sodic  carbonate  to  near  neutrality,  then 
alternately  a  drop  or  two  of  first  mercury,  then  soda,  the  exact 
point  was  reached  at  20  c.c.  of  mercury;  and  when  10  c.c.  of  the 
mercury  solution  which  gave  this  reaction  were  analyzed  as  sulphide- 
by  weight,  a  mean  of  several  determinations  gave  0'7726  gm.  of 
HgO,  which  agrees  very  closely  with  Liebig's  number. 

In  the  case  of  titrating  urine,  the  following  method  is  adopted: — 

A  plate  of  colourless  glass  is  laid  upon  black  cloth,  and  some  drops  of  a 
thick  mixture  of  sodic  bicarbonate  (free  from  carbonate)  and  water  placed 
upon  it  at  convenient  distances.  The  mercury  solution  is  added  to  the  urine 
in  such  volume  as  is  judged  appropriate,  and  from  time  to  time  a  drop  of  the 
white  mixture  is  placed  beside  the  bicarbonate  so  as  to  touch,  but  not  mix 
completely.  At  first  the  urine  mixture  remains  snow-white,  but  with 
further  additions  of  mercury  a  point  at  last  occurs  when  the  white  gives 


§  86.  URINE.  359 

place  to  yellow.  When  the  colour  has  developed  itself,  both  drops  are  rubbed 
quickly  together  with  a  glass  rod :  the  colour  should  disappear.  Further 
addition  of  mercury  is  made  cautiously  until  a  faint  yellow  is  permanent. 
Now  is  the  time  to  neutralize  by  the  addition  of  the  normal  soda  to  near  the 
volume  which  has  been  found  necessary  to  completely  neutralize  a  given 
volume  of  mercury  solution.  If  the  time  has  not  been  too  long  in  reaching 
this  point,  it  will  be  found  that  a  few  tenths  of  a  c.c.  will  suffice  to  complete 
the  reaction.  If,  however,  much  time  has  been  consumed,  it  may  occur  that, 
notwithstanding  the  mixture  is  distinctly  acid,  the  addition  of  soda  produces 
a  more  or  less  yellow  colour :  in  this  case,  nothing  is  left  but  to  go  over  the 
analysis  again,  taking  the  first  trial  as  a  guide  for  the  quantities  of  mercury 
and  soda  solutions,  which  should  be  delivered  in  one  after  the  other  as 
speedily  as  possible  until  the  exact  end  is  reached. 

It  is  absolutely  necessary,  with  this  modified  process,  to  render 
the  urine  perfectly  neutral,  after  it  is  freed  from  phosphates  and 
sulphates  by  baryta  solution. 

Corrections  and  Modifications  (Liebig). — In  certain  cases  the  results 
obtained  by  the  above  methods  are  not  strictly  correct,  owing  to  the  variable 
state  of  dilution  of  the  liquid,  or  the  presence  of  matters  which  affect  the 
mercury  solution.  The  errors  are,  however,  generally  so  slight  as  not  to 
need  correction.  Without  entering  into  a  full  description  of  their  origin, 
I  shall  simply  record  the  facts,  and  give  the  modifications  necessary  to  be 
made  where  thought  desirable. 

The  Urine  contains  more  than  2  per  cent,  of  Urea,  i.e.,  more 
than  20  parts  per  1000.  This  quantity  of  urea  would  necessitate  20  c.c. 
of  mercurial  solution  for  10  c.c.  of  urine.  All  that  is  necessary  to  be  done 
when  the  first  titration  has  shown  that  over  2  per  cent,  is  present,  is  to  add 
half  as  much  water  to  the  urine  in  the  second  titration  as  has  been  needed  of 
the  mercurial  solution  above  20  c.c.  Suppose  that  28  c.c.  have  been  used  at 
first,  the  excess  is  8  c.c.,  therefore  4  c.c.  of  water  are  added  to  the  fluid  before 
the  second  experiment  is  made. 

The  Urine  contains  less  than  2  per  cent,  of  Urea.  In  this  case, 
for  every  4  c.c.  of  mercurial  solution  less  than  20,  O'l  c.c.  must  be  deducted, 
before  calculating  the  quantity  of  urea ;  so  that  if  16  c.c.  have  been  required 
to  produce  the  yellow  colour  with  10  c.c.  urine,  15'9  is  to  be  considered  the 
correct  quantity. 

The  Urine  contains  more  than  1  per  cent,  of  Sodic  Chloride, 
i.e.,  more  than  10  parts  per  1000.  In  this  case  2  c.c.  must  be  deducted  from 
the  quantity  of  mercurial  solution  actually  required  to  produce  the  yellow 
colour,  with  10  c.c.  of  urine. 

The  Urine  contains  Albumen.  In  this  case  50  c.c.  of  the  urine  are 
boiled  with  2  drops  of  strong  acetic  acid  to  coagulate  the  albumen,  the 
precipitate  allowed  to  settle  thoroughly,  and  30  c.c.  of  the  clear  liquid  mixed 
with  15  c.c.  of  baryta  solution,  filtered,  and  titrated  for  both  chlorides  and 
urea,  as  previously  described. 

The  Urine  contains  Ammonic  Carbonate.  The  presence  of  this 
substance  is  brought  about  by  the  decomposition  of  urea,  and  it  may 
sometimes  be  of  interest  to  know  the  quantity  thus  produced,  so  as  to 
calculate  it  into  urea. 

As  its  presence  interferes  with  the  correct  estimation  of  urea  direct,  by 
mercurial  solution,  a  portion  of  the  urine  is  precipitated  with  baryta  as 
usual,  and  a  quantity,  representing  10  c.c.  of  urine,  evaporated  to  dryness  in 
the  water  bath  to  expel  the  ammonia,  the  residue  then  dissolved  in  a  little 


360  YOLUMETEIC  ANALYSIS.  §    86. 

water,  and  the  urea  estimated  in  the  ordinary  way.  On  the  other  hand, 
50  or  100  c.c.  of  the  urine,  not  precipitated  with  baryta,  are  titrated  with 
normal  sulphuric  acid  and  litmus  paper,  each  c.c.  of  acid  representing 
0'017  gm.  of  ammonia,  or  0'03  gm.  of  urea. 

Pfliiger's  correction  for  concentration  of  the  urea  differs  from 
Liebig's,  his  rule  being  as  follows  : — 

Given  the  volume  of  urea  solution + the  volume  of  NaCO3  required + the 
volume  of  any  other  fluid  free  from  urea  which  may  he  added,  and  call  this 
V1 ;  the  volume  of  mercury  solution  is  V2 ;  the  correction,  C,  is  then 

C=  — (V1— V2)  x  0-08. 

This  formula  holds  good  for  cases  where  the  total  mixture  is  less  than  three 
times  the  volume  of  mercury  used. 

With  more  concentrated  solutions  this  formula  gives  results  too  high. 

Pf  eif  f  er  (Zeit.  f.  Biol.  xx.  540)  has  made  a  careful  comparison 
of  Liebig's  (as  modified  by  Pf  lliger)  and  Kautenberg's  methods 
of  estimating  urea.  The  essential  difference  of  Rautenberg's 
method  consists  in  maintaining  the  urea  solution  neutral  throughout 
by  successive  additions  of  calcic  carbonate ;  under  these  conditions, 
the  composition  of  the  precipitate  differs  from  that  formed  when 
the  titration  is  made  according  to  Pfliiger's  process,  a  fact  which 
accounts  for  the  diminished  consumption  of  mercuric  nitrate  in  the 
former  method.  The  general  conclusions  from  his  observations 
may  be  summarized  as  follows: — (1)  In  estimating  the  correction 
for  sodic  chloride,  the  amount  of  free  acid  should  be  as  small  as 
possible,  and  0*1  c.c.  should  be  subtracted  from  every  c.c.  of 
mercuric  nitrate  used,  but  in  human  urine  it  is  preferable  to 
precipitate  the  chlorine  with  silver  nitrate,  as  a  slight  excess  of  the 
latter  does  not  influence  the  result.  (2)  The  coefficient  for 
dilution  should  be  determined  afresh  for  every  new  standard 
solution. 


4.     Estimation   of   tJrea   by  its   conversion  into   Nitrogen   Gas. 

If  a  solution  of  urea  is  mingled  with,  an  alkaline  solution  of 
hypochlorite  or  hypobromite,  the  urea  is  rapidly  decomposed  and 
nitrogen  evolved,  which  can  be  collected  and  measured  in  any  of 
the  usual  forms  of  gas  apparatus  described  in  the  section  on 
analysis  of  gases. 

Test  experiments  with  pure  urea  have  shown,  that  the  whole  of 
the  nitrogen  contained  in  it  is  eliminated  in  this  process,  with  the 
exception  of  a  constant  deficit  of  8  per  cent.  In  the  case  of  urine 
there  are  other  nitrogenous  constituents  present,  such  as  uric  acid, 
hippuric  acid,  and  creatinine,  which  render  up  a  small  proportion 
of  their  nitrogen  in  the  process,  but  the  quantity  so  obtained  is 
insignificant,  and  may  be  disregarded.  Consequently,  for  all 
medical  purposes,  this  method  of  estimating  urea  in  urine  is 
sufficiently  exact. 


§  86. 


URINE. 


361 


In  the  case  of  diabetic  urines,  however,  Mehu  and  others  have 
pointed  out  that  this  deficiency  is  diminished,  and  if,  in  addition 
to  the  glucose  present,  cane  sugar  be  also  added,  it  will  almost 
entirely  disappear.  Mehu  therefore  recommends  that  in  the 
analysis  of  saccharine  urines  cane  sugar  be  added  to  ten  times  the 
amount  of  urea  present,  when  the  difference  between  the  actual  and 
theoretical  yield  of  nitrogen  will  not  exceed  1  per  cent  (Bull.  Soc. 
Chim.  [2]  xxxiii.  410). 

Kussell  and  West  (/.  C.  S.  [2]  xii.  749)  have  described  a 
very  convenient  apparatus  for  working  the  process,  and  which  gives 
very  good  results  in  a  short  space  of  time.  This  method  has  given 
rise  to  endless  forms  of  apparatus  devised  by  various  operators, 
including  Mehu,  Yvon,  Dupre,  Apjohn,  Maxwell  Simpson, 
O'Keefe,  etc.,  etc. :  the  principles  of  construction  are  all,  however, 
the  same.  Those  who  may  wish  to  construct  simple  forms  of 
apparatus  from  ordinary  laboratory  appliances,  will  do  well  to  refer 
to  the  arrangements  of  Dupre  (/.  C.  S.  1877,  534)  or  Maxwell 
Simpson  (ibid.  538). 

The  apparatus  devised  by  Russell  and  West  is  shown  in 
fig.  45,  and  may  be  described  as  follows  : — 

The  tube  for  decomposing  the  urine 
is  about  9  inches  long,  and  about  half 
an  inch  inside  diameter.  At  2  inches 
from  its  closed  end  it  is  narrowed,  and 
an  elongated  bulb  is  blown,  leaving  the 
orifice  at  its  neck  §  of  an  inch  in 
diameter;  the  bulb  should  hold  about 
12  c.c.  The  mouth  of  this  tube  is 
fixed  into  the  bottom  of  a  tin  tray 
about  If  inch  deep,  which  acts  as  a 
pneumatic  trough ;  the  tray  is  supported 
on  legs  long  enough  to  allow  of  a 
small  spirit  lamp  being  held  under  the 
bulb  tube.  The  measuring  tube  for 
collecting  the  nitrogen  is  graduated  into 
cubic  centimeters,  and  of  such  size  as 
to  fit  over  the  mouth  of  the  decom- 
posing tube ;  one  holding  about  40  c.c. 
is  a  convenient  size.  Eussell  and  West 
have  fixed  by  experiment  the  propor- 
tions, so  as  to  obviate  the  necessity  for 
correction  of  pressure  and  temperature,  namely,  37 "1  c.c.  =  0'1  gm. 
of  urea,  since  they  found  that  5  c.c.  of  a  2  per  cent,  solution  of 
urea  constantly  gave  37'1  c.c.  of  nitrogen  at  ordinary  temperatures 
and  pressures.  The  entire  apparatus  can  be  purchased  of  most 
operative  chemists  for  a  moderate  sum. 

Hypobromite  Solution. — This  is  best  prepared  by  dissolving 
100  gm.  of  caustic  soda  in  250  c.c.  of  water  and  adding  25  c.c.  of 


Tig.  45. 


362  VOLUMETEIC  ANALYSIS.  §    86. 

bromine ;  this  mixture  gives  a  rapid  and  complete  decomposition 
of  the  urea.  It  is  always  best  prepared  in  small  quantities  as 
required.  Strong  solution  of  sodic  or  calcic  hypochlorite  answers 
equally  well,  and  possesses  the  advantage  of  keeping  better. 

The  Analysis :  5  c.c.  of  the  urine  are  measured  into  the  bulb-tube,  fixed 
in  its  proper  position,  and  the  sides  of  the  tube  washed  down  with  distilled 
water  so  that  the  bulb  is  filled  up  to  its  constriction.  A  glass  rod,  having 
a  thin  band  of  india-rubber  on  its  end,  is  then  passed  down  into  the  tube  so 
as  to  plug  up  the  narrow  opening  of  the  bulb.  The  hypobromite  solution  is 
then  poured  into  the  upper  part  of  the  tube  until  it  is  full,  and  the  trough 
is  afterwards  half  filled  with  water. 

The  graduated  tube  is  filled  with  water,  the  thumb  placed  on  the  open  end, 
and  the  tube  is  inverted  in  the  trough.  The  glass  rod  is  then  pulled  out, 
and  the  graduated  tube  slipped  over  the  mouth  of  the  bulb-tube. 

The  reaction  commences  immediately,  and  a  torrent  of  gas  rises  into  the 
measuring  tube.  To  prevent  any  of  the  gas  being  forced  out  by  the  reaction, 
the  upper  part  of  the  bulb-tube  is  slightly  narrowed,  so  that  the  gas  is  directed 
to  the  centre  of  the  graduated  tube.  With  the  strength  of  hypobromite 
solution  above  described,  the  reaction  is  complete  in  the  cold  in  about  ten  or 
fifteen  minutes ;  but  in  order  to  expedite  it,  the  bulb  is  slightly  warmed. 
This  causes  the  mixing  to  take  place  more  rapidly,  and  the  reaction  is  then 
complete  in  five  minutes.  The  reaction  will  be  rapid  and  complete  only 
when  there  is  considerable  excess  of  the  hypobromite  present.  After  the 
reaction  the  liquid  should  still  have  the  characteristic  colour  of  the 
hypobromite  solution. 

The  amount  of  constriction  in  the  tube  is  by  no  means  a  matter 
of  indifference,  as  the  rapidity  with  which  the  reaction  takes  place 
depends  upon  it.  If  the  liquids  mix  too  quickly,  the  evolution  of 
the  gas  is  so  rapid  that  loss  may  occur.  On  the  other  hand,  if  the 
tube  is  too  much  constricted,  the  reaction  takes  place  too  slowly. 

The  simplest  means  of  supporting  the  measuring  tube  is  to  have 
the  bulb-tube  corked  into  a  well,  which  projects  from  the  bottom  of 
the  trough  about  one  inch  downwards.  The  graduated  tube  stands 
over  the  bulb-tube,  and  rests  upon  the  cork  in  the  bottom  of  the 
well.  It  is  convenient  to  have,  at  the  other  end  of  the  trough, 
another  well,  which  will  form  a  support  for  the  measuring  tube 
when  not  in  use. 

To  avoid  all  calculations,  the  measuring  tube  is  graduated  so  that 
the  amount  of  gas  read  off  expresses  at  once  what  may  be  called 
the  percentage  amount  of  urea  in  the  urine  experimented  upon ; 
i.e.  the  number  of  grams  in  100  c.c.,  5  c.c.  being  the  quantity  of 
urine  taken  in  each  case.  The  gas  collected  is  nitrogen  saturated 
with  aqueous  vapour,  and  the  bulk  will  obviously  be  more  or  less 
affected  by  temperature  and  pressure.  Alterations  of  the  barometer 
produce  so  small  an  alteration  in  the  volume  of  the  gas,  that  it 
may  be  generally  neglected ;  e.g.  if  there  are  30  c.c.  of  nitrogen, 
the  quantity  preferred,  an  alteration  of  one  inch  in  the  height  of 
barometer  would  produce  an  error  in  the  amount  of  urea  of  about 
0'003  ;  but  for  more  exact  experiments,  the  correction  for  pressure 
should  be  introduced. 

In  the  wards  of  hospitals,  and  in  rooms  where  the  experiments 


§  86.  TJKINE.  363 

are  most  likely  to  be  made,  the  temperature  will  not  vary  much 
from  65°  F.,  and  a  fortunate  compensation  of  errors  occurs  with 
this  form  of  apparatus  under  these  circumstances.  The  tension  of 
the  aqueous  vapour,  together  with  the  expansion  of  the  gas  at  this 
temperature,  almost  exactly  counterbalances  the  loss  of  nitrogen 
in  the  reaction. 

The  authors  found  from  experience  that  5  c.c.  of  urine  is  the 
most  advantageous  quantity  to  employ,  as  it  usually  evolves  a  con- 
venient bulk  of  gas  to  experiment  with,  i.e.  about  30  c.c.  They 
have  shown  that  5  c.c.  of  a  standard  solution  containing  2  per  cent, 
of  urea  evolve  37*1  c.c.  of  nitrogen,  and  have  consequently  taken 
this  as  the  basis  of  the  graduation  of  the  measuring  tube.  This 
bulk  of  gas  is  read  off  at  once  as  2  per  cent,  of  urea,  and  in  the 
same  way  the  other  graduations  on  the  tube  represent  percentage 
amounts  of  urea. 

If  the  urine  experimented  with  is  very  rich  in  urea,  so  that  the 
5  c.c.  evolve  a  much  larger  volume  of  gas  than  30  c.c.,  then  it  is 
best  at  once  to  dilute  the  urine  with  its  own  bulk  of  water ;  take 
5  c.c.  of  this  diluted  urine,  and  multiply  the  volume  of  gas  obtained 
by  two. 

If  the  urine  contains  much  albumen,  this  interferes  with  the 
process  so  far  that  it  takes  a  long  time  for  the  bubbles  of  gas  to 
subside,  before  the  volume  of  gas  obtained  can  be  accurately  read 
off.  It  is  therefore  better  in  such  cases  to  remove  as  much  as 
possible  of  the  albumen  by  heating  the  urine  with  two  or  three 
drops  of  acetic  acid,  filtering,  and  then  using  the  filtrate  in  the 
usual  manner. 

The  hypobromite  method  of  estimating  urea  has  given  rise  to 
much  discussion  during  the  last  few  years,  and  among  other 
contributions,  there  occurs  one  from  Dr.  Wormley,  which  negatives 
the  idea  that  there  is  necessarily  a  loss  of  nitrogen  by  this  process 
(C.  N.  xlv.  27). 

This  operator  gives  the  result  of  his  experiments  as  follows  : — 

For  the  purpose  of  examining  the  accuracy  of  this  process  for  urea, 
without  the  presence  of  cane  sugar  or  glucose,  the  form  of  apparatus, 
at  least  in  principle,  advised  by  Apjohn  (C.  N.  xxxi.  37)  was 
employed.  This  consists  of  a  wide-mouthed  bottle  in  which  is 
placed  the  reagent,  and  also  a  small  test-tube,  for  containing  the 
urea  solution,  of  about  10  c.c.  capacity  and  of  such  length  as  to 
stand  inclined  in  the  bottle.  The  mouth  of  the  bottle  is  closed 
with  a  rubber  stopper  carrying  a  glass  tube,  by  which  it  is  connected 
by  rubber  tubing  to  a  graduated  burette  divided  into  0*1  c.c.  and 
suspended  in  a  long  cylinder  of  water  from  an  adjustable  arm. 

The  urea  solution  is  placed  in  the  small  tube  within  the  charged 
bottle,  the  apparatus  closed,  and  when  there  is  no  longer  any  change 
in  the  height  of  the  column  of  liquid  within  the  graduated  tube, 
this  is  so  adjusted  that  the  surface  of  the  contained  liquid  exactly 
coincides  with  that  in  the  cylinder.  This  point,  the  temperature, 


364  VOLUMETRIC  ANALYSIS.  §    86. 

and  in  exact  experiments  the  barometric  pressure,  being  noted,  the 
urea  solution  is  mixed  with  the  reagent  by  inclining  the  bottle  and 
gently  shaking  the  mixture.  As  the  evolved  nitrogen  collects  in 
the  burette,  the  latter  is  gradually  raised  to  relieve  the  contained 
gas  from  the  increased  pressure.  When  the  evolution  of  gas  has 
entirely  ceased  and  there  is  no  longer  any  change  in  the  volume  of 
gas,  the  tube  is  finally  adjusted  and  the  exact  volume  noted.  The 
hypobromite  employed  was  the  same  as  described  p.  361.  In 
applying  the  reagent,  it  was  diluted  with  a  volume  and  a  half  of 
pure  water. 

With  this  arrangement  a  series  of  experiments  was  performed 
employing  1  c.c.  of  a  standard  solution  of  pure  urea  varying  in 
strength  from  1  to  6  per  cent.,  variously  diluted,  and  added  to 
varying  quantities  of  the  reagent.  These  experiments  gave  different 
results,  in  some  only  about  90  per  cent.,  and  even  less,  of  the 
nitrogen  being  evolved,  while  in  others  a  larger  proportion  was 
obtained,  and  in  still  others  the  icliole  of  the  nitrogen  was  set  free. 
It  was  finally  observed  that  under  certain  conditions  the  whole  of 
the  nitrogen  is  uniformly  eliminated.  These  conditions  are  : — 

1.  The  reagent  should  be  freshly  prepared. 

2.  The  urea  solution  should  be  wholly  added  to  the  reagent, 
none  of  the  latter  being  allowed  to  mix  with  the  urea  solution  in 
the  containing  tube. 

3.  The  amount  of  urea  operated  upon  should  not  exceed  one 
part  to  about  twelve  hundred  parts  of  the  diluted  reagent. 

Moreover,  the  diluted  urea  solution  should  be  added  in  small 
portions  at  a  time  to  the  reagent,  thoroughly  mixed,  and  the 
effervescence  allowed  to  cease  before  any  further  addition  of  urea. 
So,  also,  it  would  appear,  at  least  when  comparatively  large 
quantities  of  urea  are  present,  that  the  surrounding  temperature 
should  not  be  less  than  about  20°  C.  (68°  R). 

In  the  practical  application  of  the  test,  if  a  2  per  cent,  solution 
of  urea  is  under  examination,  1  c.c.  of  the  solution,  diluted  with 
from  5  to  10  c.c.  water,  is  placed  in  the  containing  tube,  and  the 
mixing  bottle  charged  with  10  c.c.  of  the  reagent  diluted  with 
15  c.c.  of  water;  whereas,  for  1  c.c.  of  a  4  per  cent,  solution  of 
urea,  similarly  diluted,  not  less  than  about  50  c.c.  of  the  diluted 
reagent  should  be  employed. 

In  a  final  series  of  experiments,  in  which  the  above  conditions 
were  observed,  the  temperature  being  noted  to  ^  of  a  degree,  and 
the  results  reduced  to  the  standard  temperature  and  pressure,  the 
following  average  results  were  obtained : — 

Urea  employed.  Nitrogen  evolved = 

10  milligrams  9*98  rn.gm.  urea. 

20         „  20-07      „ 

30         „  29-95      „ 

40  39-88      „ 


§    86.  URINE. 

In  these  experiments  it  was  assumed  that  1  gm.  of  urea 
contains  372  c.c.  of  nitrogen,  measured  at  0°  C.  and  760  m.m. 
barometric  pressure;  or,  that  each  c.c.  of  nitrogen  evolved, 
measured  under  the  conditions  stated,  represented  0'002688  gm. 
urea. 

During  these  investigations  it  was  observed,  in  cases  in 
which  the  whole  of  the  nitrogen  was  not  evolved,  that  so  long 
as  the  conditions  remained  the  same,  the  relative  proportion 
of  the  nitrogen  eliminated  was  pretty  uniform.  Hence,  if 
the  volume  of  nitrogen  evolved  from  a  known  quantity  of 
urea  under  certain  conditions,  or  by  a  given  form  of  apparatus, 
be  determined,  the  result  may  be  taken  as  the  basis  for  the 
determination  of  the  urea  in  the  urine  with  sufficient  accuracy 
for  clinical  purposes. 

Hamburger  (Zeit.  f.  Biol.  xx.  286)  refers  to  Pfliiger's 
modification  of  Liebig's  method,  which  although  an  improvement 
leaves  much  to  be  desired;  his  own  method  is  founded  on 
Quinquand's  (Monit.  Scien.  1882,  2),  in  which  the  de- 
composition of  urea  by  sodic  hypobromite  is  supposed  to  take 
place  thus : — 

3jSTaBr  +  2H20  +  CO2  +  W. 

This  reaction  requires  the  proportion  of  bromine,  sodic  hydrate,  and 
water  to  be  exactly  balanced  or  incorrect  results  will  be  obtained. 
The  author  claims  for  his  method  that  it  will  yield  correct  results, 
no  matter  in  wrhat  proportions  these  reagents  are  present.  It 
consists  essentially  in  adding  an  excess  of  an  alkaline  solution 
of  sodic  hypobromite  of  known  strength  to  the  liquid  containing 
urea,  then  destroying  the  excess  of  hypobromite  with  an  excess  of 
standard  sodic  arsenite  (=19 '8  gm.  As203  per  liter),  and  finally 
determining  the  amount  of  arsenite  remaining  unoxidized,  by 
titration  with  standard  iodine  solution,  the  amount  of  urea  then 
being  readily  calculated  from  the  amount  of  sodic  arsenite 
remaining  unoxidized.  The  author's  experiments  as  to  the  accuracy 
of  the  method,  show  that  a  certain  quantity  of  urea  always 
requires  the  same  amount  of  hypobromite,  and  that  the  dilution  of 
the  solution  of  urea  has  no  effect  on  the  quantity  of  hypobromite 
employed. 

To  decide  on  the  applicability  of  the  method  to  natural  urine, 
great  pains  were  taken,  the  urea  being  determined  as  described,  the 
effect  of  its  dilution  with  water  studied,  pure  urea  added,  and  the 
whole  estimated,  and  lastly  sodic  hypobromite  of  various  degrees  of 
concentration  employed ;  the  results  of  the  experiments  are  given 
very  fully  and  tabulated.  On  the  whole,  they  are  very  satisfactory, 
the  differences  falling  well  within  the  limits  of  errors  of  observation 
and  manipulation :  the  method  is  therefore  considered  applicable  to 
the  determination  of  urea  in  urine. 


366  VOLUMETRIC   ANALYSIS.  §    86. 

5.    Estimation  of  Phosphoric  Acid   (see   also   §   69). 

The  principle  of  this  method  is  fully  described  at  page  273. 
The  following  solutions  are  required  : — 

(1)  Standard   Uranic   acetate  or  nitrate.       1   c.c.  =  0*005  gm. 
P205  (see  p.  274). 

(2)  Standard  Phosphoric  acid  (see  p.  275). 

(3)  Solution  of  Sodic  acetate  (see  p.  274). 

(4)  Solution   of  Potassic  ferrocyanide. — About   1    part   to  20 
of  water,  freshly  prepared,  or  some  of  the  finely  powdered  salt. 

The  Analysis :  50  c.c.  of  the  clear  urine  are  measured  into  a  small  beaker, 
together  with  5  c.c.  of  the  solution  of  sodic  acetate  (if  uranic  nitrate  is  used). 
The  mixture  is  then  warmed  in  the  water  bath,  or  otherwise,  and  the  uranium 
solution  delivered  in  from  the  burette,  with  constant  stirring,  as  long  as  a 
precipitate  is  seen  to  occur.  A  small  portion  of  the  mixture  is  then  removed 
with  a  glass  rod  and  tested  as  described  (p.  275)  ;  so  long  as  no  brown  colour 
is  produced,  the  addition  of  uranium  may  be  continued ;  when  the  faintest 
indication  of  this  reaction  is  seen,  the  process  must  be  stopped,  and  the 
amount  of  colour  observed.  If  it  coincides  with  the  original  testing  of  the 
uranium  solution  with  a  similar  quantity  of  fluid,  the  result  is  satisfactory, 
and  the  quantity  of  solution  used  may  be  calculated  for  the  total  phosphoric 
acid  contained  in  the  50  c.c.  of  urine;  if  the  uranium  has  been  used 
accidentally  in  too  great  quantity,  10  or  20  c.c.  of  the  same  urine  may  be 
added,  and  the  testing  concluded  more  cautiously.  Suppose,  for  example,  that 
the  solution  has  been  added  in  the  right  proportion,  and  19'2  c.c.  used,  the 
50  c.c.  will  have  contained  0'096  gm.  phosphoric  acid  (  =  T92  per  100).  With 
care  and  some  little  practice  the  results  are  very  satisfactory. 

Earthy  Phosphates. — The  above  determination  gives  the  total  amount 
of  phosphoric  acid,  but  it  may  sometimes  be  of  interest  to  know  how  much  of 
it  is  combined  with  lime  and  magnesia.  To  this  end  100  or  200  c.c.  of  the 
urine  are  measured  into  a  beaker,  and  rendered  freely  alkaline  with  ammonia ; 
the  vessel  is  then  set  aside  for  ten  or  twelve  hours,  for  the  precipitate  of 
earthy  phosphates  to  settle :  the  clear  fluid  is  then  decanted  through  a  filter, 
the  precipitate  brought  upon  it  and  washed  with  ammoniacal  water;  a 
hole  is  then  made  in  the  filter  and  the  precipitate  washed  through;  the 
paper  moistened  with  a  little  acetic  acid,  and  washed  into  the  vessel 
containing  the  precipitate,  which  latter  is  dissolved  in  acetic  acid,  some  sodic 
acetate  added,  and  the  mixture  diluted  to  about  50  c.c.  and  titrated  as  before 
described ;  the  quantity  of  phosphoric  acid  so  found  is  deducted  from  the 
total  previously  estimated,  and  the  remainder  gives  the  quantity  existing  in 
combination  with  alkalies. 


6.    Estimation   of  the   Sulphuric  Acid. 

Standard  Baric  chloride. — A  quantity  of  crystallized  baric 
chloride  is  to  be  powdered,  and  dried  between  folds  of  blotting- 
paper.  Of  this,  30-5  gm.  are  dissolved  in  distilled  water,  and  the 
liquid  made  up  to  a  liter.  1  c.c.  =  0'01  gm.  of  SO3. 

Solution  of  Sodic  sulphate. — 1  part  to  10  of  water. 


§  86.  URINE.  367 

The  Analysis :  100  c.c.  of  the  urine  are  poured  into  a  beaker,  a  little 
hydrochloric  acid  added,  and  the  whole  placed  on  a  small  sand  bath,  to 
which  heat  is  applied.  When  the  solution  boils,  the  baric  chloride  is  allowed 
to  flow  in  very  gradually  as  long  as  the  precipitate  is  seen  distinctly  to 
increase.  The  heat  is  removed,  and  the  vessel  allowed  to  stand  still,  so 
that  the  precipitate  may  subside.  Another  drop  or  two  is  then  added,  and 
so  on,  until  the  whole  of  the  SO3  is  precipitated.  Much  time,  however,  is 
saved  by  using  Be  ale's  filter,  represented  in  fig.  19.  A  little  of  the  fluid 
is  thus  filtered  clear,  poured  into  a  test-tube,  and  tested  with  a  drop  from 
the  burette ;  this  is  afterwards  returned  to  the  beaker,  and  more  of  the  test 
solution  added,  if  necessary.  The  operation  is  repeated  until  the  precipita- 
tion is  complete.  In  order  to  be  sure  that  too  much  of  the  baryta  solution 
has  not  been  added,  a  drop  of  the  clear  fluid  is  added  to  the  solution  of  sodic 
sulphate  placed  in  a  test-tube  or  upon  a  small  mirror  (see  §  73.3).  If  no 
precipitate  occurs,  more  baryta  must  be  added ;  if  a  slight  cloudiness  takes 
place,  the  analysis  is  finished;  but  if  much  precipitate  is  produced,  too 
large  a  quantity  of  the  test  has  been  used,  and  the  analysis  must  be  repeated. 

For  instance,  suppose  that  18 '5  c.c.  have  been  added,  and  there 
is  still  a  slight  cloudiness  produced  which  no  longer  increases  after 
the  addition  of  another  J-  c.c.,  we  know  that  between  18 \  and 
19  c.c.  of  solution  have  been  required  to  precipitate  the  whole  of 
the  sulphuric  acid  present,  and  that  accordingly  the  100  c.c.  of 
urine  contain  between  0*185  and  0*19  gm.  of  SO3. 


7.    Estimation   of  Sugar. 

Feh ling's  original  method  is  precisely  the  same  as  described 
in  §  71,  but  if  the  urine  has  decomposed  so  as  to  contain 
ammonia  or  ammonic  carbonate,  this  method  must  be  discarded 
and  Pavy's  or  Knapp's  solution  used. 

The  Analysis :  10  c.c.  of  the  clear  urine  are  diluted  by  means  of  a 
measuring  flask  to  200  c.c.  with  water,  and  a  large  burette  filled  with  the 
fluid;  10  c.c.  of  the  copper  solution  (=0'05  gm.  of  sugar)  are  then  measured 
into  a  white  porcelain  capsule,  40  c.c.  of  distilled  water  added,  the  vessel 
arranged  over  a  spirit  or  gas  lamp  under  the  burette,  and  brought  to 
boiling ;  the  diluted  urine  is  then  delivered  in  cautiously  from  the  burette 
until  the  bluish  colour  has  nearly  disappeared.  The  addition  of  the  urine 
must  then  be  continued  more  carefully,  allowing  the  red  precipitate  to  subside 
after  each  addition  by  removing  the  heat,  when  by  gently  sloping  the  capsule, 
the  clear  liquid  allows  the  white  sides  of  the  capsule  to  be  seen,  so  that  the 
faintest  shade  of  blue  would  be  at  once  perceptible.  When  the  colour  is  all 
removed,  the  burette  is  read  off,  and  the  quantity  of  sugar  in  the  urine 
calculated  as  follows : — 

Suppose  that  40  c.c.  of  the  diluted  urine  have  been  required  to  reduce 
the  10  c.c.  of  copper  solution,  that  quantity  will  have  contained  0'05  gm.  of 
sugar ;  but,  the  urine  being  diluted  20  times,  the  40  c.c.  represent  only  2  c.c. 
of  the  original  urine ;  therefore  2  c.c.  of  it  contain  0'05  gm.  of  sugar,  or 
25  parts  per  1000. 

The  Pavy-Fehling  solution  is  much  more  generally  adapted  to 
urine,  and  is  prepared  and  used  precisely  as  described  in  §  71. 

The  Analysis:  10  c.c.  of  clear  urine  are  diluted  as  just  described,  and 
delivered  cautiously  from  the  burette  into  50  or  100  c.c.  of  the  Pavy- 


368  VOLUMETEIC  ANALYSIS.  §    86. 

Fehling  liquid  (previously  heated  to  boiling)  until  the  colour  is  discharged. 
The  calculation  is  the  same  as  before.  100  c.c.  of  Pavy-Fehling  solution 
=0*05  gin.  glucose. 

The  ammoniacal  fumes  are  best  absorbed  by  leading  an  elastic  tube 
from  the  reduction  flask  into  a  beaker  of  water  ;  the  end  of  the  tube  should 
be  plugged  with  a  piece  of  solid  glass  rod,  and  a  transverse  slit  made  in  the 
elastic  tube  just  above  the  plug.  This  valve  allows  the  vapours  to  escape, 
but  prevents  the  return  of  the  liquid  in  case  of  a  vacuum. 

Knapp's  solution,  which  is  equally  applicable  to  urine,  is 
described  on  p.  296,  and  possesses  the  advantage  over  the  Pavy 
solution  that  no  objectionable  fumes  are  given  off. 

The  Analysis:  10,  20,  or  40  c.c.  of  Knapp's  solution  is  diluted  with 
four  volumes  of  water,  and  heated  to  boiling.  The  diluted  urine  containing 
from  half  to  one  per  cent,  of  sugar  is  then  gradually  added  until  all  the 
mercury  is  precipitated,  as  shown  by  the  method  of  testing  given  on  p.  296. 
Each  10  c.c.  of  solution=0'025  gm.  of  sugar. 


8.    Estimation   of  Uric   Acid. 

The  determination  of  uric  acid  in  urine  is  not  often  considered 
of  much  consequence ;  there  are,  however,  circumstances  under 
which  it  is  desirable,  especially  in  urinary  deposits.  As  the 
quantity  present  in  urine  is  very  small,  it  is  necessary  to  take,  say, 
from  200  to  500  c.c.  for  the  estimation. 

The  urine  being  measured  into  a  beaker,  from  5  to  8  c.c.  of  pure  hydro- 
chloric acid  are  added,  the  whole  well  mixed,  covered  with  a  glass  plate,  and 
set  aside  in  a  cellar  for  24  or  30  hours  ;*  at  the  end  of  that  time  the  uric  acid 
will  be  precipitated  in  small  crystals  upon  the  bottom  and  sides  of  the  beaker. 
The  supernatant  liquid  is  decanted,  washed  once  with  cold  distilled  water, 
then  dissolved  in  a  small  quantity  of  pure  solution  of  potash  diluted  to 
150  c.c.  or  so  with  distilled  water,  acidified  strongly  with  sulphuric  acid,  and 
titrated  precisely  as  oxalic  acid  (§  30.2  c),  with  ^V  permanganate,  each  c.c.  of 
which  is  equal  to  0'0075  gm.  of  uric  acid.  This  method  is  'not  absolutely 
correct,  owing  to  the  fact  that  with  the  uric  acid  there  is  always  precipitated 
a  certain  amount  of  colouring  matter  of  the  urine,  which  destroys  the  per- 
manganate equally  with  the  uric  acid.  The  method  by  weighing  is,  however, 
open  to  the  same  objection,  beside  being  very  troublesome,  so  that  no 
advantage  is  gained  by  the  latter  plan.  Has  sail  states  that  the  normal 
quantity  of  uric  acid  in  urine  has  hitherto  been  considerably  under-estimated, 
and  that  if  the  urine  is  concentrated  by  evaporation  before  precipitating 
with  hydrochloric  acid,  a  much  larger  quantity  will  be  obtained  (Lancet, 
Feb.  1865). 

Haycraft  (Brit.  Med.  Journ.  1885,  1100)  has  devised  a  method 
of  estimating  uric  acid,  which  although  it  cannot  be  said  to  be 
absolutely  accurate,  is  capable  of  giving  fairly  good  results  in  the 
hands  of  a  careful  operator.  The  method  is  based  on  the  fact 
that  uric  acid  combines  with  silver  as  silver  urate,  which  is 
practically  insoluble  in  water,  ammonia,  or  acetic  acid,  but  perfectly 

*If  200  c.c.  of  urine  are  violently  agitated  for  five  minutes  with  5  c.c,  of  fuming 
HC1,  the  separation  will  be  complete  in  an  hour. 


§  86.  URINE..  369 

soluble  in  nitric  acid.  The  chief  drawback  to  the  method  is  the 
peculiar  nature  of  the  precipitate  of  silver  urate,  which  is  slimy 
and  difficult  to  wash ;  this,  however,  is  overcome  by  collecting  the 
precipitate  on  an  asbestos  filter  attached  to  a  filter  pump.  The 
filter  is  easily  made  by  half  filling  a  small  funnel  with  broken 
glass,  upon  which  small  asbestos  fibres  suspended  in  water  are 
poured  to  the  depth  of  J  inch  and  evenly  distributed.  Such 
a  filter  may  be  used  repeatedly  for  the  same  operation.  The 
estimation  of  the  uric  acid  depends  upon  the  titration  of  the 
silver  with  which  it  is  combined,  by  Volhard's  method  (§  39). 
The  necessary  solutions  are — • 

TJ^  Ammonic  thiocyanate. — Standardized  by  a  silver  solution 
of  known  strength.  1  c.c.  =  0*00168  gm.  uric  acid. 

Ammoniacal  Silver  solution. — 5  gm.  silver  nitrate  in  about 
100  c.c.  of  water,  precipitated  and  re-dissolved  in  ammonia  to  a 
clear  solution. 

Ferric  indicator  and  pure  Nitric  acid. — The  same  as  described 
in  §39. 

The  Analysis:  25  c.c.  of  urine  arc  placed  in  a  small  "beaker,  together 
with  about  1  gm.  of  sodic  bicarbonate  and  2  or  3  drops  of  strong  ammonia. 
This  precipitates  ammonio-magnesic  phosphate  and  prevents  reduction  of 
silver.  1 — 2  c.c.  of  ammoniacal  silver  solution  are  then  added,  which  at  once 
precipitates  the  silver  as  urate.  The  mixture  is  now  placed  on  the  filter,  and 
washed  until  the  washings  show  no  trace  of  silver  by  testing  with  salt. 
The  precipitate  is  then  dissolved  in  a  few  c.c.  of  nitric  acid,  washed  into  a 
flask,  and  the  titration  carried  out  precisely  as  described  in  §  39.  The 
number  of  c.c.  of  thiocyanate  used  multiplied  by  0'00168  gives  the  uric  acid. 

If  the  urine  to  be  examined  contains  albumen,  it  must  be  first 
removed  by  acidifying  slightly  with  acetic  acid,  heating,  and 
filtering.* 


9.    Estimation  of  lame   and  Magnesia. 

100  c.c.  of  the  urine  are  precipitated  with  ammonia,  the  precipitate 
re-dissolved  in  acetic  acid,  and  sufficient  ammonic  oxalate  added  to  precipitate 
all  the  lime  present  as  oxalate.  The  precipitate  is  allowed  to  settle  in  a  warm 
place,  then  the  clear  liquid  passed  through  a  small  filter,  the  precipitate 
brought  upon  it,  washed  with  hot  water,  the  filtrate  and  washings  set  aside, 
then  the  precipitate,  together  with  the  filter,  pushed  through  the  funnel  into 
a  flask,  some  sulphuric  acid  added,  the  liquid  freely  diluted,  and  titrated  with 
permanganate,  precisely  as  in  §  48 ;  each  c.c.  of  ^j-  permanganate  required 
represents  0'0028  gm.  of  CaO. 

*  It  has  been  suggested  to  shorten  this  method  by  using  an  exactly  known  amount 
of  silver  which  shall  be  in  excess,  diluting  to  a  definite  measure,  then  filtering  off  an 
aliquot  portion  through  an  ordinary  filter,  and  estimating  the  excess,  thus  finding 
the  amount  combined  as  urate.  This  avoids  the  tedious  filtration  and  washing  of 
the  precipitate,  and  gives  results  agreeing  with  the  original  method  with  pure 
solutions  of  uric  acid.  With  urine  both  methods  are  variable  as  compared  with 
other  methods,  due  probably,  to  obscure  causes.  Much  discussion  has  arisen 
among  physiological  chemists  as  to  the  various  methods  of  estimating  uric  acid, 
and  a  convenient  exact  method  is  still  much  wanted. 

B   B 


370  VOLUMETRIC   ANALYSIS.  §    86. 

Instead  of  the  above  method  the  following  may  be  adopted : — 

The  precipitate  of  calcic  oxalate,  after  being  washed,  is  dried  and,  together 
with  the  filter,  ignited  in  a  platinum  or  porcelain  crucible,  by  which  means 
it  is  converted  into  a  mixture  of  calcic  oxide  and  carbonate.  It  is  then 
transferred  to  a  flask  by  the  aid  of  the  washing  bottle,  and  an  excess  of  ^5- 
nitric  acid  delivered  in  with  a  pipette.  The  amount  of  acid,  over  and  above 
what  is  required  to  saturate  the  lime,  is  found  by  T^  caustic  alkali,  each  c.c. 
of  acid  being  equal  to  0'0028  gm.  of  CaO. 

In  examining  urinary  sediment  or  calculi  for  calcic  oxalate,  it  is 
first  treated  with  caustic  potash  to  remove  uric  acid  and  organic 
matter,  then  dissolved  in  sulphuric  acid,  freely  diluted,  and  titrated 
with  permanganate ;  each  c.c.  of  £j  solution  represents  0'0054  gm. 
of  calcic  oxalate. 

Magnesia. — The  nitrate  and  washings  from  the  precipitate  of 
calcic  oxalate  are  evaporated  011  the  water  bath  to  a  small  bulk, 
then  made  alkaline  with  ammonia,  sodic  phosphate  added,  and  set 
aside  for  8  or  10  hours  in  a  slightly  warm  place,  that  the  magnesia 
may  separate  as  ammonio-magnesic  phosphate.  The  supernatant 
liquid  is  then  passed  through  a  small  filter,  the  precipitate  brought 
upon  it,  washed  with  ammoniacal  water  in  the  cold,  and  dissolved  in 
acetic  acid,  then  titrated  with  uranium  solution,  as  in  §  69 ;  each 
c.c.  of  solution  required  represents  OO02815  gm.  of  magnesia. 


10.    Ammonia. 

The  only  method  hitherto  applied  to  the  determination  of  am- 
monia in  urine  is  that  of  Schlbsing,  which  consists  in  placing  a 
measured  quantity  of  the  urine,  to  which  milk  of  lime  is  previously 
added,  under  an  air-tight  bell-glass,  together  with  an  open  vessel 
containing  a  measured  quantity  of  titrated  acid.  In  the  course  of 
from  24  to  36  hours  all  the  ammonia  will  have  passed  out  of  the 
urine  into  the  acid,  which  is  then  titrated  with  standard  alkali  to 
find  the  amount  of  ammonia  absorbed. 

One  great  objection  to  this  method  is  the  length  of  time  required, 
since  no  heating  must  be  allowed,  urea  being  decomposed  into  free 
ammonia,  when  heated  with  alkali.  There  is  also  the  uncertainty 
as  to  the  completion  of  the  process ;  and  if  the  vessel  be  opened 
before  the  absorption  is  perfect,  the  analysis  is  spoiled.  The 
following  plan  is  recommended  as  in  most  cases  suitable : — When 
a  solution  containing  salts  of  ammonia  is  mixed  with  a  measured 
quantity  of  free  fixed  alkali  of  known  strength,  and  boiled  until 
ammoniacal  gas  ceases  to  be  evolved,  it  is  found  that  the  resulting 
liquid  has  lost  so  much  of  the  free  alkali  as  corresponds  to  the 
ammonia  evolved  (§  18) ;  that  is  to  say,  the  acid  which  existed  in 
combination  with  the  ammonia  in  the  original  liquid  has  simply 
changed  places,  taking  so  much  of  the  fixed  alkali  (potash  or  soda) 


§  86.  UKINE.  371 

as  is  equivalent  to  the  ammonia  it  has  left  to  go  free.  In  the  .case 
of  urine  being  treated  in  this  way,  the  urea  will  also  be  decomposed 
into  free  ammonia,  but  happily  in  such  a  way  as  not  to  interfere 
with  the  estimation  of  the  original  amount  of  ammoniacal  salts. 
The  decomposition  is  such  that,  while  free  ammonia  is  evolved  from 
the  splitting  up  of  the  urea,  carbonate  of  fixed  alkali  (say  potash) 
is  formed  in  the  boiling  liquid,  and  as  this  reacts  equally  as  alkaline 
as  though  it  were  free  potash,  it  does  not  interfere  in  the  slightest 
degree  with  the  estimation  of  the  original  ammonia. 
The  following  is  the  best  method  of  procedure  : — 

100  c.c.  of  the  urine  are  exactly  neutralized  with  £$  soda  or  potash,  as  for 
the  estimation  of  free  acid;  it  is  then  put  into  a  flask  capable  of  holding 
five  or  six  times  the  quantity,  10  c.c.  of  normal  alkali  added,  and  the 
whole  brought  to  boiling,  taking  care  that  the  bladders  of  froth  which  at 
first  form  do  not  boil  over.  After  a  few  minutes  these  subside,  and  the  boiling 
proceeds  quietly.  When  all  ammoniacal  fumes  are  dissipated,  the  lamp  is 
removed,  and  the  flask  allowed  to  cool  slightly ;  the  contents  then  emptied 
into  a  tall  beaker,  and  normal  nitric  acid  delivered  in  from  the  burette  with 
constant  stirring,  until  a  fine  glass  rod  or  small  feather  dipped  in  the  mixture 
and  brought  in  contact  with  violet-coloured  litmus  paper  produces  neither 
a  blue  nor  a  red  spot.  The  number  of  c.c.  of  normal  acid  are  deducted  from 
the  10  c.c.  of  alkali,  and  the  rest  calculated  as  ammonia.  1  c.c.  of  alkali= 
0'017  gm.  of  ammonia. 

Example :  100  c.c.  of  urine  were  taken,  and  required  7  c.c.  of  ^  alkali 
to  saturate  its  free  acid ;  10  c.c.  of  normal  alkali  were  then  added,  and  the 
mixture  boiled  until  a  piece  of  moistened  red  litmus  paper  was  not  turned 
blue  when  held  in  the  steam;  4'5  c.c.  of  normal  acid  were  afterwards  required 
to  saturate  the  free  alkali ;  the  quantity  of  ammonia  was  therefore  equal  to 
5'5  c.c.,  which,  multiplied  by  0'017,  gave  0'0935  gm.  in  1000  of  urine. 

It  must  be  borne  in  mind,  that  the  plan  just  described  is  not  applicable  to 
urine  which  has  already  suffered  decomposition  by  age  or  other  circumstances 
so  as  to  contain  carbonate  of  ammonia ;  in  this  case  it  would  be  preferable  to 
adopt  Schlosing's  method;  or  where  no  other  free  alkali  is  present,  direct 
titration  with  normal  acid  may  be  adopted.  • 


11.    Estimation   of  Free   Acid. 

The  acidity  of  urine  is  doubtless  owing  to  variable  substances, 
among  the  most  prominent  of  which  appear  to  be  acid  sodic  phos- 
phate and  lactic  acid.  Other  free  organic  acids  are  probably  in  many 
cases  present.  Under  these  circumstances,  the  degree  of  acidity 
cannot  be  placed  to  the  account  of  any  particular  body ;  neverthe- 
less, it  is  frequently  desirable  to  ascertain  its  amount,  which  is  best 
done  as  follows  : — 

100  c.c.  of  urine  are  measured  into  a  beaker,  and  ^  alkali  delivered  in 
from  a  small  burette,  until  a  thin  glass  rod  or  feather,  moistened  with  the 
mixture  and  streaked  across  some  well-prepared  violet  litmus  paper,  produces 
no  change  of  colour ;  the  degree  of  acidity  is  then  registered  as  being  equal 
to  the  quantity  of  T^-  alkali  used. 

B  B  2 


372  VOLUMETRIC   ANALYSIS.  §    86. 

12.    Estimation   of  Albximen. 

(a)  By  Weight :  100  c.c.  of  the  clear  urine  (or  less  than  that  quantity 
if  much  albumen  is  present,  the  100  c.c.  being  made  up  with  water)  are 
introduced  into  a  good-sized  beaker,  and  heated  in  the  water  bath  for  half  an 
hour.  If  the  urine  is  sufficiently  acid,  the  albumen  will  be  separated  in 
flocks.  Should  this  not  be  the  case  at  the  end  of  the  half-hour's  heating., 
and  the  fluid  merely  appears  turbid,  one  or  two  drops  (not  more,  unless  the 
urine  is  alkaline)  of  acetic  acid  are  added,  and  the  heating  continued  until 
the  albumen  separates  in  flocks;  the  beaker  is  then  put  aside  till  the 
precipitate  has  settled,  and  the  clear  liquid  passed  through  a  small  filter 
(previously  dried  at  212°,  then  cooled  between  two  watch-glasses  held  together 
with  a  spring  clip,  and  weighed)  ;  the  precipitate  is  then  washed  with  a 
little  hot  water,  and  brought  upon  the  filter  without  loss,  the  beaker  washed 
out  with  hot  distilled  water,  and  the  last  traces  of  precipitate  loosened  from 
the  sides  with  a  feather.  The  filter,  with  its  contents,  is  then  repeatedly 
washed  with  hot  water,  until  a  drop  of  the  filtrate  evaporated  on  a  piece 
of  glass  leaves  no  residue.  The  funnel  containing  the  filter  is  then  put 
into  a  warm  place  to  dry  gradually;  lastly,  the  filter  removed  into  one  of  the 
watch-glasses  and  dried  thoroughly  in  the  air  bath  at  110°  C.,  or  220°  Fahr. ; 
another  watch-glass  is  then  covered  over  that  containing  the  filter,  the  spring 
clip  passed  over  to  hold  them  together,  the  whole  cooled  under  the  exsiccator 
and  weighed.  The  weight  of  the  glasses,  filter,  and  clip,  deducted  from  the 
total,  gives  the  weight  of  albumen  in  100  c.c.  of  urine. 

(J)  By  Measure:  In  order  to  avoid  the  tedious  process  of  estimating  the 
albumen  as  just  described,  Bode ker  devised  a  method  of  titration  which 
gives  approximate  results  when  the  quantity  of  albumen  is  not  too  small,  say 
not  less  than  2  per  cent.  The  principle  is  based  on  the  fact  that,  potassic 
ferrocyanide  completely  precipitates  albumen  from  an  acetic  acid  solution  in 
the  atomic  proportions  of  211  ferrocyanide  to  1612  albumen. 

Standard  Solution  of  Ferrocyanide. — 1'309  gm.  of  the  pure 
salt  in  a  liter  of  distilled  water.  1  c.c.  of  the  solution  precipitates 
O'Ol  gm.  of  albumen.  It  must  be  freshly  prepared. 

The  Analysis :  50  c.c.  of  the  clear  filtered  urine  are  mixed  with  50  c.c. 
of  ordinary  commercial  acetic  acid,  and  the  fluid  put  into  a  burette.  Five 
or  six  small  filters  are  then  chosen,  of  close  texture,  and  put  into  as  many 
funnels,  then  moistened  with  a  few  drops  of  acetic  acid,  and  filled  up  with 
boiling  water ;  by  this  means  the  subsequent  clear  filtration  of  the  mixture 
is  considerably  facilitated.  10  c.c.  of  the  ferrocyanide  solution  are  then 
measured  into  a  beaker,  and  10  c.c.  of  the  urinary  fluid  from  the  burette 
added,  well  shaken,  and  poured  upon  filter  No.  1.  If  the  fluid  which 
passes  through  is  bright  and  clear  with  yellowish  colour,  the  ferrocyanide 
will  be  in  excess,  and  a  drop  of  the  urine  added  to  it  will  produce  a  cloudiness. 
On  the  other  hand,  if  not  enough  ferrocyanide  has  been  added,  the  filtrate 
will  be  turbid,  and  pass  through  very  slowly ;  in  this  case,  frequently  both 
the  ferrocyanide  and  the  urine  will  produce  a  turbidity  when  added.  In 
testing  the  filtrate  for  excess  of  ferrocyanide,  care  must  be  taken  not  to  add 
too  much  of  the  urine,  lest  the  precipitate  of  hydroferrocyanide  of  albumen 
should  dissolve  in  the  excess  of  albumen. 

According  to  the  results  obtained  from  the  first  filter,  a  second  trial  is  made, 
increasing  the  quantity  of  urine  or  ferrocyanide  half  or  as  much  again,  and 
so  on  until  it  is  found  that  the  solution  first  shown  to  be  in  excess  is  reversed. 
A  trial  of  the  mean  between  this  quantity  and  the  previous  one  will  bring- 
the  estimation  closer,  so  that  a  final  test  may  be  decisive. 

Example:  50  c.c.  of  urine  passed  by  a  patient  suffering  from  B right's 


I  87.  URINE.  373 

disease  were  mixed  with  the  like  quantity  of  acetic  acid,  and  tested  as 
follows : — 

In  filtrate 

Urine.  Ferrocyanide.        Urine    Ferrocyanide 

gave 

1.  10  c.c.  10  c.c.  0  prec. 

2.  10    „  20    „  prec.  0 

3.  10    „  15    „  0  prec. 

4.  10    „  17'5,,  0  faint  prec. 

5.  10    „  18    „  0  0 

Therefore  the  10  c.c.  of   diluted  urine  (  =  5  c.c.   of  the  original 
secretion)  contained  0*18  gm.  albumen,  or  36  parts  per  1000. 

13.    Estimation   of  Soda   and  Potash. 

50  c.c.  of  urine  are  mixed  with  the  same  quantity  of  baryta  solution, 
allowed  to  stand  a  short  time,  and  filtered;  then  80  c.c.  (  =  40  c,c.  urine) 
measured  into  a  platinum  dish  and  evaporated  to  dryness  in  the  water  bath ; 
the  residue  is  then  ignited  to  destroy  all  organic  matter,  and  when  cold 
dissolved  in  a  small  quantity  of  hot  water,  ammonic  carbonate  added  so  long 
as  a  precipitate  occurs,  filtered  through  a  small  filter,  the  precipitate  washed, 
the  filtrate  acidified  with  hydrochloric  acid  and  evaporated  to  dryness,  then 
cautiously  heated  to  expel  all  ammoniacal  salts.  The  residue  is  then  treated 
with  a  little  water  and  a  few  drops  each  of  ammonia  and  ammonic  carbonate, 
filtered,  the  filter  thoroughly  washed,  the  filtrate  and  washings  received  into  a 
tared  platinum  dish,  then  evaporated  to  dryness,  ignited,  cooled,  and  weighed. 

By  this  means  the  total  amount  of  mixed  sodic  and  potassic 
chlorides  is  obtained.  The  proportion  of  each  is  found  by  titrating 
for  the  chlorine  as  in  §  38,  and  calculating  as  directed  on  page  126. 


14.     Estimation   of   Total  Nitrogen. 

This  can  now  be  easily  accomplished  by  KjeldahPs  method 
(§  18.5)  and  is  especially  serviceable,  since  it  has  been  found  that 
the  results  of  the  titration  method  for  urea  by  Liebig's  process, 
either  in  its  original  way  or  by  subsequent  modifications,  cannot 
give  the  true  data  for  calculating  the  nitrogen  in  any  given  specimen 
of  urine. 

The  Analysis :  5  c.c.  of  urine  of  average  concentration  are  measured 
into  a  flask  holding  about  300  c.c.,  together  with  20  c.c.  of  sulphuric  acid, 
then  heated  to  boiling,  and  the  heat  continued  until  all  vapour  and  gases 
are  given  off  and  the  fluid  possesses  a  clear  yellow  tint.  25  to  30  minutes 
generally  suffices.  The  flask  is  then  suffered  to  cool,  the  liquid  diluted,  and 
distilled  with  caustic  soda  and  zinc  as  described  on  page  79. 


ANALYSIS     OF     NATURAL     WATERS     AND     SEWAGE. 

§  87.  THE  analysis  of  natural  waters  and  sewage  has  for  a  long 
period  received  the  attention  of  chemists,  but  until  lately  no 
methods  of  examination  have  been  produced  which  could  be  said 
to  satisfy  the  demands  of  those  who  have  been  interested  in  the 
subject  from  various  points  of  view.  The  researches  of  Clark, 


374  VOLUMETRIC  ANALYSIS.  §    87. 

Frankland,  Miller,  Wanklyn,  Tidy,  Bischof,  Warington, 
and  others,  have,  however,  now  brought  the  whole  subject  into  a 
more  satisfactory  form,  so  that  it  may  fairly  be  said  that,  as  regards 
accuracy  of  chemical  processes,  or  interpretation  of  results  from  a 
sanitary  point  of  view,  very  little  addition  is  required.  Consider- 
able space  will  be  devoted  to  the  matter  here ;  and  as  most  of  the 
processes  are  now  volumetric,  and  admit  of  ready  and  accurate 
results,  the  general  subject  naturally  falls  within  the  scope  of  this 
work.  Considerable  pains  have  been  taken  to  render  the  treatment 
of  the  matter  practical  and  trustworthy. 

Since  the  various  processes  necessitate  the  use  of  peculiar 
materials  and  apparatus,  the  preparation  and  arrangement  of  these 
will  be  described  at  some  length  previous  to  the  introduction  of  the 
general  subject. 

THE  PREPARATION  OF  REAGENTS. 

A.     Reagents  required  for  the  Estimation  of  Nitrogen  present  as 

Ammonia. 

•  (a)  Nessler's  Solution. — Dissolve  6 2 '5  gm.  of  potassic  iodide 
in  about  250  c.c.  of  distilled  water,  set  aside  a  few  c.c.,  and  add 
gradually  to  the  larger  part  a  cold  saturated  solution  of  corrosive 
sublimate  until  the  mercuric  iodide  precipitated  ceases  to  be 
redissolved  on  stirring.  When  a  permanent  precipitate  is  obtained, 
restore  the  reserved  potassic  iodide  so  as  to  redissolve  it,  and 
continue  adding  corrosive  sublimate  very  gradually  until  a  slight 
precipitate  remains  undissolved.  (The  small  quantity  of  potassic 
iodide  is  set  aside  merely  to  enable  the  mixture  to  be  made  rapidly 
without  danger  of  adding  an  excess  of  corrosive  sublimate.) 

Next  dissolve  150  gm.  of  solid  potassic  hydrate  (that  usually 
sold  in  sticks  or  cakes)  in  150  c.c.  of  distilled  wrater,  allow  the 
solution  to  cool,  add  it  gradually  to  the  above  solution,  and  make 
up  with  distilled  water  to  one  liter. 

On  standing,  a  brown  precipitate  is  deposited,  and  the  solution 
becomes  clear,  and  of  a  pale  greenish-yellow  colour.  It  is  ready 
for  use  as  soon  as  it  is  perfectly  clear,  and  should  be  decanted  into 
a  smaller  bottle  as  required. 

(/3)  Standard  Solution  of  Ammonic  chloride. — Dissolve  1-9107 
gm.  of  pure  dry  ammonic  chloride  in  a  liter  of  distilled  water ;  of 
this  take  100  c.c.,  and  make  up  to  a  liter  with  distilled  water. 
The  latter  solution  will  contain  ammonic  chloride  corresponding  to 
0-00005  gm.  of  nitrogen  in  each  c.c.  In  use  it  should  be  measured 
from  a  narrow  burette  of  10  c.c.  capacity  divided  into  tenths. 

[If  it  is  desired  to  estimate  "ammonia"  rather  than  "nitrogen  as 
ammonia,"  take  1'5735  gm.  of  ammonic  chloride  instead  of  1'9107  gm. 
1  c.c.  will  then  correspond  to  O'OOOOS  gm.  of  ammonia  (NH3).] 

(y)     Sodic    carbonate. — Heat    anhydrous    sodic    carbonate    to 


§    87.  NATURAL  WATERS   AND   SEWAGE.  S75 

redness  in  a  platinum  crucible  for  about  an  hour,  taking  care 
not  to  fuse  it.  Whilst  still  warm  rub  it  in  a  clean  mortar  so  as  to 
break  any  lumps  which  may  have  been  formed,  and  transfer  to 
a  clean  dry  wide-mouthed  stoppered  bottle. 

(3)  "Water  free  from  Ammonia. — If,  when  1  c.c.  of  Kessler's 
solution  (A.  a)  is  added  to  100  c.c.  of  distilled  water  in  a  glass 
cylinder,  standing  on  a  white  surface  (see  Estimation  of  Ammonia), 
no  trace  of  a  yellow  tint  is  visible  after  five  minutes,  the  water  is 
sufficiently  pure  for  use.  As,  however,  this  is  rarely  the  case,  the 
following  process  must  usually  be  adopted.  Distil  from  a  large 
glass  retort  (or  better,  from  a  copper  or  tin  vessel  holding  15 — 20 
liters)  ordinary  distilled  water  which  has  been  rendered  distinctly 
alkaline  by  addition  of  sodic  carbonate.  A  glass  Liebig's 
condenser,  or  a  clean  tin  worm  should  be  used  to  condense  the 
vapour ;  it  should  be  connected  to  the  still  by  a  short  india-rubber 
joint.  Test  the  distillate  from  time  to  time  with  Nessler's 
solution,  as  above  described,  and  when  free  from  ammonia  collect 
the  remainder  for  use.  The  distillation  must  not  be  carried  to 
dryness.  Ordinary  water  may  be  used  instead  of  distilled  water, 
but  it  occasionally  continues  for  some  time  to  give  off  traces  of 
ammonia  by  the  slow  decomposition  of  the  organic  matter  present 
in  it. 


B.     Reagents  required  for  the  Estimation  of  Organic  Carbon  and 

Nitrogen. 

(a)  Water  free  from  Ammonia  and  Organic  Matter. — Distilled 
water,  to  which  1  gm.  of  potassic  hydrate  and  0'2  gm.  of  potassic 
permanganate  per  liter  have  been  added,  is  boiled  gently  for  about 
twenty-four  hours  in  a  similar  vessel  to  that  used  in  preparing 
water  free  from  ammonia  (A.  £),  an  inverted  condenser  being  so 
arranged  as  to  return  the  condensed  water.  At  the  end  of  that 
time  the  condenser  is  adjusted  in  the  usual  way,  and  the  water 
carefully  distilled,  the  distillate  being  tested  at  intervals  for 
ammonia,  as  in  preparing  A.  &  When  ammonia  is  no  longer 
found  the  remainder  of  the  distillate  may  be  collected,  taking  care 
to  stop  short  of  dryness.  The  neck  of  the  retort  or  still  should 
point  slightly  upwards,  so  that  the  joint  which  connects  it  with 
the  condenser  is  the  highest  point.  Any  particles  carried  up 
mechanically  will  then  run  back  to  the  still,  and  not  contaminate 
the  distillate.  The  water  thus  obtained  should  then  be  rendered 
slightly  acid  with  sulphuric  acid,  and  re-distilled  from  a  clean 
vessel  for  use,  again  stopping  short  of  dryness. 

(/3)  Solution  of  Sulphurous  acid. — Sulphurous  anhydride  is 
prepared  by  the  action  of  pure  sulphuric  acid  upon  cuttings  of 
clean  metallic  copper  which  have  been  digested  in  the  cold  with 
concentrated  sulphuric  acid  for  twenty-four  hours,  and  then  washed 


376  •'-       VOLUMETRIC  ANALYSIS.  §    87. 

with  water.  The  gas  is  made  to  bubble  through  water  to  remove 
mechanical  impurities,  and  then  conducted  into  water  free  from 
ammonia  and  organic  matter  (B.  a)  until  a  saturated  solution  is 
obtained. 

(y)  Solution  of  Hydric  sodic  sulphite. — Sulphurous  anhydride, 
prepared  and  washed  as  above,  is  passed  into  a  solution  of  sodic 
carbonate  made  by  dissolving  ignited  sodic  carbonate  (A.  y)  in 
water  free  from  ammonia  and  organic  matter  (B.  a).  The  gas  is 
passed  until  carbonic  anhydride  ceases  to  be  evolved. 

(£)  Solution  of  Ferrous  chloride. — Pure  crystallized  ferrous 
sulphate  is  dissolved  in  water,  precipitated  by  sodic  hydrate,  the 
precipitate  well  washed  (using  pure  water  B.  a  for  the  last 
washings),  and  dissolved  in  the  smallest  possible  quantity  of  pure 
hydrochloric  acid.  Two  or  three  drops  must  not  contain  an 
appreciable  quantity  of  ammonia.  It  is  convenient  to  keep  the 
solution  in  a  bottle  with  a  ground  glass  cap  instead  of  a  stopper, 
so  that  a  small  dropping  tube  may  be  kept  in  it  always  ready 
for  use. 

(«)  Cupric  oxide. — Prepared  by  heating  to  redness  with  free 
access  of  air,  on  the  hearth  of  a  reverberatory  furnace,  or  in 
a  muffle,  copper  wire  cut  into  short  pieces,  or  copper  sheets  cut  into 
strips.  That  which  has  been  made  by  calcining  the  nitrate  cannot 
be  used,  as  it  appears  to  be  impossible  to  expel  the  last  traces  of 
nitrogen.  After  use,  the  oxide  should  be  extracted  by  breaking 
the  combustion  tube,  rejecting  the  portion  which  was  mixed  with 
the  substance  examined.  As  soon  as  a  sufficient  quantity  has  been 
recovered,  it  should  be  recalcined.  This  is  most  conveniently 
done  in  an  iron  tube  about  30  m.m.  in  internal  diameter,  and  about 
the  same  length  as  the  combustion  furnace.  One  end  should  be 
closed  with  a  cork,  the  cupric  oxide  poured  in,  the  tube  placed  in 
the  combustion  furnace  (which  is  tilted  at  an  angle  of  about  15°, 
so  as  to  produce  a  current  of  air),  the  cork  removed,  and  the  tube 
kept  at  a  red  heat  for  about  two  hours.  In  a  Hofmann.'s  gas 
furnace,  with  five  rows  of  burners,  two  such  tubes  may  be  heated 
at  the  same  time  if  long  clay  burners  are  placed  in  the  outer  rows, 
and  short  ones  in  the  three  inner  rows.  If  the  furnace  has  but 
three  rows  of  burners,  a  rather  smaller  iron  tube  must  be  used. 
When  cold,  the  oxide  can  easily  be  extracted,  if  the  heat  has  not 
been  excessive,  by  means  of  a  stout  iron  wire,  and  should  be  kept 
in  a  clean  dry  stoppered  bottle.  Each  parcel  thus  calcined  should 
invariably  be  assayed  by  filling  with  it  a  combustion  tube  of  the 
usual  size,  and  treating  it  in  every  respect  as  an  ordinary  combustion. 
It  should  yield  only  a  very  minute  bubble  of  gas,  which  should  be 
almost  wholly  absorbed  by  potassic  hydrate.  (The  quantity  of 
CO2  found  should  not  correspond  to  more  than  0*00005  gm.  of  C, 
otherwise  the  oxide  must  be  recalcined).  The  finer  portions  of  the 


§    87.  NATURAL   WATERS   AND   SEWAGE.  377 

oxide  should,  after  calcining,  be  sifted  out  by  means  of  a  sieve  of 
clean  copper  gauze,  and  reserved  for  use  as  described  hereafter. 

New  cupric  oxide  as  obtained  from  the  reverberatory  furnace 
should  be  assayed,  and  if  not  sufficiently  pure,  as  is  most  likely  the 
case,  calcined  as  above  described,  and  assayed  again. 

(£)  Metallic  Copper. — Fine  copper  gauze  is  cut  into  strips 
about  80  m.m.  wide,  and  rolled  up  as  tightly  as  possible  on 
a  copper  wire  so  as  to  form  a  compact  cylinder  80  m.m.  long.  This 
is  next  covered  with  a  tight  case  of  moderately  thin  sheet  copper, 
the  edges  of  which  meet  without  overlapping.  The  length  of  the 
strip  of  gauze,  and  the  consequent  diameter  of  the  cylinder,  must 
be  regulated  so  that  it  will  fit  easily,  but  not  too  loosely  in  the 
combustion  tubes.  A  sufficient  number  of  these  cylinders  being 
prepared,  a  piece  of  combustion  tube  is  filled  with  them,  and  they 
are  heated  to  redness  in  the  furnace,  a  current  of  atmospheric  air 
being  passed  through  them  for  a  few  minutes  in  order  to  burn  off 
organic  impurity,  and  coat  the  copper  gauze  superficially  with 
oxide.  A  current  of  hydrogen,  dried  by  passing  through  strong 
sulphuric  acid,  is  then  substituted  for  the  air,  and  a  red  heat 
maintained  until  hydrogen  issues  freely  from  the  end  of  the  tube. 
It  is  then  allowed  to  cool,  the  current  of  hydrogen  being  continued, 
and  when  cold  the  copper  cylinders  are  removed,  and  kept  in 
a  stoppered  bottle.  After  being  used  several  times  they  must  be 
heated  in  a  stream  of  hydrogen  as  before,  and  are  then  again  ready 
for  use.  The  heating  in  air  need  not  be  repeated. 

(?/)  Solution  of  Potassic  bichromate. — This  is  used  as  a  test 
for  and  to  absorb  sulphurous  anhydride  which  may  be  present  in 
the  gas  obtained  by  combustion  of  the  water  residue.  It  should 
be  saturated,  and  does  not  require  any  special  attention.  The 
yellow  neutral  chromate  may  also  be  used,  but  must  be  rendered 
slightly  acid,  lest  it  should  absorb  carbonic  as  well  as  sulphurous 
anhydride. 

(0)  Solution  of  Potassic  hydrate. — A  cold  saturated  solution, 
made  by  dissolving  solid  potassic  hydrate  in  distilled  water. 

(t)  Solution  of  Pyrogallic  acid. — A  cold  saturated  solution, 
made  by  dissolving  in  distilled  water  solid  pyrogallic  acid  obtained 
by  sublimation. 

(ic)  Solution  of  Cuprous  chloride. — A  saturated  solution  of 
cupric  chloride  is  rendered  strongly  acid  with  hydrochloric  acid, 
a  quantity  of  metallic  copper  introduced  in  the  form  of  wire  or 
turnings,  and  the  whole  allowed  to  stand  in  a  closely  stoppered 
bottle  until  the  solution  becomes  colourless. 

(X)  Oxygen. — Blow  a  bulb  of  about  30  c.c.  capacity  at  the  end 
of  a  piece  of  combustion  tube,  and  draw  out  the  tube  so  that  its 
internal  diameter  for  a  length  of  about  300  m.m.  is  about  3  m.m. 


378  VOLUMETRIC  ANALYSIS.  §    87. 

This  is  done  in  order  that  the  capacity  of  the  apparatus  apart  from 
the  bulb  may  be  as  small  as  possible.  Cut  the  tube  at  the  wide 
part  about  10  m.m.  from  the  point  at  which  the  narrow  tube 
commences,  thus  leaving  a  small  funnel-shaped  mouth.  Then 
introduce,  a  little  at  a  time,  dried,  coarsely  powdered,  potassic 
chlorate  until  the  bulb  is  full.  Cut  off  the  funnel,  and,  at 
a  distance  of  100  m.m.  from  the  bulb,  bend  the  tube  at  an  angle  of 
45°,  and  at  10  m.m.  from  the  end  bend  it  at  right  angles  in.  the 
opposite  direction.  It  then  forms  a  retort  and  delivery  tube  in 
one  piece,  and  must  be  adjusted  in  a  mercury  trough  in  the  usual 
manner,  taking  care  that  the  end  does  not  dip  deeper  than  about 
20  m.m.  below  the  surface,  as  otherwise  the  pressure  of  so  great 
a  column  of  mercury  might  destroy  the  bulb  when  softened  by  heat. 
On  gently  heating,  the  potassic  chlorate  fuses  and  evolves  oxygen. 
The  escaping  gas  is  collected  in  test  tubes  about  150  m.m.  long 
and  20  m.m.  in  diameter,  rejecting  the  first  60  or  80  c.c.,  which 
contain  the  nitrogen  of  the  air  originally  in  the  bulb  retort.  Five 
or  more  of  these  tubes,  according  to  the  quantity  of  oxygen 
required,  are  collected  and  removed  from  the  mercury  trough,  in. 
very  small  beakers,  the  mercury  in  which  should  be  about  10  m.m. 
above  the  end  of  the  test  tube.  Oxygen  may  be  kept  in  this  way 
for  any  desired  length  of  time,  care  being  taken,  if  the  temperature 
falls  considerably,  that  there  is  sufficient  mercury  in  the  beaker  to 
keep  the  mouth  of  the  test  tube  covered.  About  10  c.c.  of  the 
gas  in  the  first  tube  collected  is  transferred  by  decantation  in 
a  mercury  trough  to  another  tube,  and  treated  with  potassic  hydrate 
and  pyrogallic  acid,  when,  if  after  a  few  minutes  it  is  absorbed, 
with  the  exception  of  a  very  small  bubble,  the  gas  in  that  and  the 
remaining  tubes  may  be  considered  pure.  If  not,  the  first  tube  is 
rejected,  and  the  second  tested  in  the  same  way,  and  so  on. 

(jj)  Hydric  metaphosphate. — The  glacial  hydric  metaphosphate, 
tisually  sold  in  sticks,  is  generally  free  from  ammonia,  or  very 
nearly  so.  A  solution  should  be  made  containing  about  100  gm. 
in  a  liter.  It  should  be  so  far  free  from  ammonia  as  that  10  c.c. 
do  not  contain  an  appreciable  quantity. 

(v)  Calcic  phosphate. — Prepared  by  precipitating  common 
disodic  phosphate  with  calcic  chloride,  washing  the  precipitate 
with  water  by  decantation,  drying,  and  heating  to  redness  for 
an  hour. 


C.    Reagents  required  for  the   Estimation   of  Nitrogen  present   as 
Nitrates   and  Nitrites    (drum's   process). 

(a)  Concentrated  Sulphuric  acid. — The  ordinary  colourless 
acid  is  usually  free  from  nitrates  and  nitrites.  It  should  be 
tested  before  use  by  the  method  described  hereafter  for  the 
estimation  of  nitrogen  as  nitrates  (§  83.6). 


§    87.  NATURAL  WATERS   AND   SEWAGE.  379 

(/3)  Potassic  permanganate. — Dissolve  about  10  gm.  of  crys- 
tallized potassic  permanganate  in  a  liter  of  distilled  water. 

(y)  Sodic  carbonate. — Dissolve  about  10  gm.  of  dry,  or  an 
equivalent  quantity  of  crystallized  sodic  carbonate  free  from 
nitrates,  in  a  liter  of  distilled  water. 


Por  the  Estimation  of  Nitrogen  as  Nitrates  and  Nitrites  in  "Waters 
containing  a  very  large  quantity  of  Soluble  Matter,  but  little 
Organic  Nitrogen. 

(2)     Metallic  Aluminium. — As  thin  foil. 

(e)  Solution  of  Sodic  hydrate. — Dissolve  100  gm.  of  solid 
sodic  hydrate  in  a  liter  of  distilled  water ;  when  cold,  put  it  in 
a  tall  glass  cylinder,  and  introduce  about  100  sq.  cm.  of  aluminium 
foil,  which  must  be  kept  at  the  bottom  of  the  solution  by  means  of 
a  glass  rod.  When  the  aluminium  is  dissolved,  boil  the  solution 
briskly  in  a  porcelain  basin  until  about  one-third  of  its  volume  has 
been  evaporated,  allow  to  cool,  and  make  up  to  its  original  volume 
with  water  free  from  ammonia.  The  absence  of  nitrates  is  thus 
ensured. 

(£)  Broken  Pumice. — Clean  pumice  is  broken  in  pieces  of  the 
size  of  small  peas,  sifted  free  from  dust,  heated  to  redness  for  about 
an  hour,  and  kept  in  a  closely  stoppered  bottle. 

(77)  Hydrochloric  acid  free  from  Ammonia. — If  the  ordinary 
pure  acid  is  not  free  from  ammonia,  it  should  be  rectified  from 
sulphuric  acid.  As  only  two  or  three  drops  are  used  in  each 
experiment,  it  will  be  sufficient  if  that  quantity  does  not  contain 
an  appreciable  proportion  of  ammonia. 

Por  the   Estimation   of  Nitrogen  as  Nitrates  and  Nitrites   by   the 
Indigo   Process. 

The  necessary  solutions  for  this  method  have  already  been  fully 
described  011  page  240. 

Por  the   Estimation   of  Nitrites   by   G-riess's   Process. 

(6)  Meta-phenylene-diamine. — A  half  per  cent,  solution  of  the 
base  in  very  dilute  sulphuric  or  hydrochloric  acid.  The  base  alone 
is  not  permanent.  If  too  highly  coloured,  it  may  be  bleached  by 
pure  animal  charcoal. 

(t)  Dilute  Sulphuric  acid. — One  volume  of  acid  to  two  of 
water. 

(K)  Standard  Potassic  or  Sodic  nitrite. — Dissolve  0*406  gm. 
of  pure  silver  nitrite  in  boiling  distilled  water,  and  add  pure 


380  VOLUMETRIC   ANALYSIS.  .§    87. 

potassic  or  sodic  chloride  till  no  further  precipitate  of  silver 
chloride  occurs.  Make  up  to  a  liter  ;  let  the  silver  chloride  settle, 
and  dilute  100  c.c.  of  the  clear  liquid  to  a  liter.  It  should  be  kept 
in  small  stoppered  bottles  completely  filled,  and  in  the  dark. 


1  c.c.  =  0-01  m.gm. 

The  colour  produced  by  the  reaction  of  nitrous  acid  011  meta- 
phenylene-diamiiie  is  triamidoazo-benzene,  or  "Bismarck  brown." 


D.    Reagents   required  for  the   Estimation   of  Chlorine   present   as 

Chloride. 

(a)  Standard  Solution  of  Silver  nitrate. — Dissolve  2 -3944 
gm.  of  pure  recrystallized  silver  nitrate  in  distilled  water,  and 
make  up  to  a  liter.  In  use  it  is  convenient  to  measure  it  from  a 
burette  which  holds  10  c.c.  and  is  divided  into  tenths. 

(/3)  Solution  of  Potassic  chr ornate. — A  strong  solution  of  pure 
neutral  potassic  chromate  free  from  chlorine.  It  is  most  con- 
veniently kept  in  a  bottle  similar  to  that  used  for  the  solution  of 
ferrous  chloride  (B.  2). 

E.    Reagents   required  for   determination   of  Hardness. 

(a)  Standard  Solution  of  Calcic  chloride. — Dissolve  in  dilute 
hydric  chloride,  in  a  platinum  dish,  0*2  gm.  of  pure  crystallized 
calcite,  adding  the  acid  gradually,  and  having  the  dish  covered 
with  a  glass  plate,  to  prevent  loss  by  spirting.  When  all  is 
dissolved,  evaporate  to  dryness  on  a  water  bath,  add  a  little  distilled 
water,  and  again  evaporate  to  dryness.  Repeat  the  evaporation 
several  times  to  ensure  complete  expulsion  of  hydric  chloride. 
Lastly,  dissolve  the  calcic  chloride  in  distilled  water,  and  make  up 
to  one  liter. 

(/3)  Standard  Solution  of  Potassic  soap. — Rub  together  in  a 
mortar  150  parts  of  lead  plaster  (Emplast.  Plumbi  of  the  druggists) 
and  40  parts  of  dry  potassic  carbonate.  When  they  are  fairly 
mixed,  add  a  little  methylated  spirit,  and  continue  triturating  until 
an  uniform  creamy  mixture  is  obtained.  Allow  to  stand  for  some 
hours,  then  throw  on  to  a  filter,  and  wash  several  times  with 
methylated  spirit.  The  strong  solution  of  soap  thus  obtained 
must  be  diluted  with  a  mixture  of  one  volume  of  distilled  water 
and  two  volumes  of  methylated  spirit  (considering  the  soap  solution 
as  spirit),  until  exactly  14 '2 5  c.c.  are  required  to  form  a  permanent 
lather  with  50  c.c.  of  the  standard  calcic  chloride  (E.  a),  the 
experiment  being  performed  precisely  as  in  determining  the  hard- 
ness of  a  water.  A  preliminary  assay  should  be  made  with  a  small 
quantity  of  the  strong  soap  solution  to  ascertain  its  strength. 
After  making  the  solution  approximately  of  the  right  strength, 


§    88.  NATUKAL  WATEIiS  AND   SEWAGE.  381 

allow  it  to  stand  twenty  four  hours ;  and  then,  if  necessary,  filter 
it,  and  afterwards  adjust  its  strength  accurately.  It  is  better  to 
make  the  solution  a  little  too  strong  at  first,  and  dilute  it  to  the 
exact  strength  required,  as  it  is  easier  to  add  alcohol  accurately 
than  strong  soap  solution. 


THE  ANALYTICAL  PROCESSES. 

§  88.  To  form,  for  sanitary  purposes,  an  opinion  of  the  character 
of  a  natural  water  or  sewage,  it  will  in  most  cases  suffice  to 
determine  the  nitrogen  as  ammonia,  organic  carbon,  organic  nitrogen, 
total  solid  matter,  nitrogen  as  nitrates  and  nitrites,  suspended 
matter,  chldrine,  and  hardness ;  and  in  the  following  pages  the 
estimation  of  these  will  be  considered  in  detail,  and  then,  more 
briefly,  that  of  other  impurities. 

The  method  of  estimating  nitrogen  as  ammonia  is  substantially 
that  described  by  the  late  W.  A.  Miller  (/.  C.  S.  [2]  iii.  125), 
and  that  for  estimating  organic  carbon  and  nitrogen  was  devised 
by  Frankland  and  Armstrong,  and  described  by  them  in  the 
same  journal  ([2]  vi.  77  et  seq.). 

1.  Collection  of  Samples. — The  points  to  be  considered  under 
this  head  are,  the  vessel  to  be  used,  the  quantity  of  water  required, 
and  the  method  of  ensuring  a  truly  representative  sample. 

Stoneware  bottles  should  be  avoided,  as  they  are  apt  to  affect  the 
hardness  of  the  water,  and  are  more  difficult  to  clean  than  glass. 
Stoppered  glass  bottles  should  be  used  if  possible ;  those  known 
as  "  Winchester  Quarts,"  which  hold  about  two  and  a  half  liters 
each,  are  very  convenient  and  easy  to  procure.  One  of  these  will 
contain  sufficient  for  the  general  analysis  of  sewage  and  largely 
polluted  rivers,  two  for  well  waters  and  ordinary  rivers  and  streams, 
and  three  for  lakes  and  mountain  springs.  If  a  more  detailed 
analysis  is  required,  of  course  a  larger  quantity  must  be  taken. 

If  corks  must  be  used,  they  should  be  neic,  and  well  washed 
with  the  water  at  the  time  of  collection. 

In  collecting  from  a  well,  river,  or  tank,  plunge  the  bottle  itself, 
if  possible,  below  the  surface ;  but  if  an  intermediate  vessel  must 
be  used,  see  that  it  is  thoroughly  clean  and  well  rinsed  with  the 
water.  Avoid  the  surface  water  and  also  any  deposit  at  the 
bottom. 

If  the  sample  is  taken  from  a  pump  or  tap,  take  care  to  let  the 
water  which  has  been  standing  in  the  pump  or  pipe  run  off  before 
collecting,  then  allow  the  stream  to  flow  directly  into  the  bottle. 
If  it  is  to  represent  a  town  water-supply,  take  it  from  the  service 
pipe  communicating  directly  with  the  street  main,  and  not  from 
a  cistern. 

In  every  case,  first  fill  the  bottle  completely  with  the  water, 
thus  expelling  all  gases  and  vapours,  empty  it  again,  rinse  once  or 


382  VOLUMETRIC  ANALYSIS.  §    88. 

twice  carefully  with  the  water,  and  then  fill  it  nearly  to  the  stopper, 
and  tie  down  tightly. 

At  the  time  of  collection  note  the  source  of  the  sample,  whether 
from  a  deep  or  shallow  well,  a  river  or  spring,  and  also  its  local 
name  so  that  it  may  be  clearly  identified. 

If  it  is  from  a  well,  ascertain  the  nature  of  the  soil,  subsoil,  and 
water-bearing  stratum;  the  depth  and  diameter  of  the  well,  its 
distance  from  neighbouring  cesspools,  drains,  or  other  sources 
of  pollution ;  whether  it  passes  through  an  impervious  stratum 
before  entering  the  water-bearing  stratum,  and  if  so,  whether  the 
sides  of  the  well  above  this  are,  or  are  not,  water-tight. 

If  the  sample  is  from  a  river,  ascertain  the  distance  from  the 
source  to  the  point  of  collection;  whether  any  pollution  takes 
place  above  that  point,  and  the  geological  nature  of  the  district 
through  which  it  flows. 

If  it  is  from  a  spring,  take  note  of  the  stratum  from  which  it 
issues. 

2.  Preliminary  Observations. — In   order  to  ensure  uniformity, 
the  bottle   should   invariably  'be  well   shaken  before   taking  out 
a  portion  of  the  sample  for  any  purpose.     The  colour  should  IDC 
observed  as  seen  in  a  tall,  narrow  cylinder  standing  upon  a  white 
surface.     It  is  well  to  compare  it  with  distilled  water  in  a  similar 
vessel.     The  taste  and  odour  are  most  easily  detected  when  the 
water  is  heated  to  30° — 35°  C. 

Before  commencing  the  quantitative  analysis,  it  is  necessary  to 
decide  whether  the  water  shall  be  filtered  or  not  before  analysis. 
This  must  depend  on  the  purpose  for  which  the  examination  is 
undertaken.  As  a  general  rule,  if  the  suspended  matter  is  to  be 
determined,  the  water  should  be  filtered  before  the  estimation  of 
organic  carbon  and  nitrogen,  nitrogen  as  ammonia,  and  total  solid 
residue;  if  otherwise,  it  should  merely  be  shaken  up.  If  the 
suspended  matter  is  not  determined,  the  appearance  of  the  water, 
as  whether  it  is  clear  or  turbid,  should  be  noted.  This  is 
conveniently  done  when  measuring  out  the  quantity  to  be  used  for 
the  estimation  of  organic  carbon  and  nitrogen.  If  the  measuring 
flask  be  held  between  the  eye  and  a  good  source  of  light,  but  with 
an  opaque  object,  such  as  a  window  bar,  in  the  line  drawn  from 
the  eye  through  the  centre  of  the  flask,  any  suspended  particles 
will  be  seen  well  illuminated  on  a  dark  ground. 

Water  derived  from  a  newly  sunk  well,  or  which  has  been 
rendered  turbid  by  the  introduction  of  innocuous  mineral  matter 
from  some  temporary  and  exceptional  cause  should  be  filtered,  but 
the  suspended  matter  in  most  such  cases  need  not  be  determined. 
The  introduction  of  organic  matter  of  any  kind  would  almost 
always  render  thr  sample  useless. 

3.  Estimation  of  Nitrogen  as  Ammonia. — Place   about  50  C.C.  of 
the  water  in  a  glass  cylinder  about  150  m.m.  high,  and  of  about 


§    88.  NATURAL  WATERS   AND   SEWAGE.  383 

70  c.c.  capacity,  standing  upon  a  white  glazed  tile  or  white  paper. 
Add  about  1  c.c.  of  Nessler's  solution  (A.  a),  stir  with  a  clean 
glass  rod,  and  allow  to  stand  for  a  minute  or  so.  If  the  colour 
then  seen  does  not  exceed  in  intensity  that  produced  when  O'l  c.c. 
of  the  standard  ammonic  chloride  (A.  /3)  is  added  to  50  c.c.  of 
water  free  from  ammonia  (A.  £),  and  treated  in  the  same  way, 
half  a  liter  of  the  water  should  be  used  for  the  estimation.  If 
the  colour  be  darker,  a  proportionately  smaller  quantity  should  be 
taken ;  but  it  is  not  convenient  to  use  less  than  20  or  25  c.c. 

If  it  has  been  decided  that  the  water  should  be  filtered  before 
analysis,  care  must  be  taken,  should  it  contain  only  a  small  quantity 
of  ammonia,  that  the  filter  paper  is  free  from  ammonia.  If  it  is 
not,  it  must  be  steeped  in  water  free  from  ammonia  for  a  day  or  so, 
and  when  used,  the  first  portion  of  the  filtrate  rejected.  Washinr/ 
with  water,  even  if  many  times  repeated,  is  generally  ineffectual. 
When  a  large  quantity  of  ammonia  is  present,  as  in  highly  polluted 
water  and  sewage,  any  ammonia  in  the  filter  paper  may  be  neglected. 
A  moderate  quantity  of  suspended  matter  may  also  generally  be 
neglected  with  safety,  even  if  the  water  is  to  be  filtered  in 
estimating  organic  carbon  and  nitrogen  and  total  solid  matter. 

The  water,  filtered  or  unfiltered  as  the  case  may  be,  should  be 
carefully  measured  and  introduced  into  a  capacious  retort,  connected 
by  an  india-rubber  joint  with  a  Liebig's  condenser,  the  volume 
being  if  necessary,  made  up  to  about  400  c.c.  with  water  free  from 
ammonia.  Add  about  1  gm.  of  sodic  carbonate  (A.  y),  and  distil 
rapidly,  applying  the  lamp  flame  directly  to  the  retort,  and  collect 
the  distillate  in  a  small  glass  cylinder,  such  as  is  described  above. 
When  about  50  c.c.  have  distilled  into  the  first  cylinder,  put  it  aside 
and  collect  a  second  50  c.c.,  and  as  soon  as  that  is  over  remove  the 
lamp,  and  add  to  the  second  distillate  about  1  c.c.  of  Nessler's 
solution,  stir  with  a  clean  glass  rod,  and  allow  to  stand  on  a  white 
tile  or  sheet  of  paper  for  five  minutes.  To  estimate  the  ammonia 
present,  measure  into  a  similar  cylinder  as  much  of  the  standard 
ammonic  chloride  solution  as  you  judge  by  the  colour  to  be  present 
in  the  distillate ;  make  it  up  with  water  free  from  ammonia  to  the 
same  volume,  and  treat  with  Nessler's  solution  in  precisely  the 
same  way.  If,  on  standing,  the  intensity  of  colour  in  the  two 
cylinders  is  equal,  the  quantity  of  ammonia  is  also  equal,  and  this 
is  known  in  the  trial  cylinder.  If  it  is  not  equal,  another  trial 
must  be  made  with  a  greater  or  less  quantity  of  ammonic  chloride. 
The  ammonic  chloride  must  not  be  added  after  the  Nessler's 
solution,  or  a  turbidity  will  be  produced  which  entirely  prevents 
accurate  comparison.  If  the  ammonia  in  the  second  distillate  does 
not  exceed  that  in  0*2  c.c.  of  the  standard  ammonic  chloride,  the 
distillation  need  not  be  proceeded  with  any  farther,  but  if  otherwise, 
successive  quantities  must  be  distilled  and  tested  until  ammonia 
ceases  to  be  found.  If  the  ammonia  in  the  second  distillate 
corresponds  to  0*4  c.c.  or  less  of  the  ammonic  chloride,  that  in  the 


384  VOLUMETRIC   ANALYSIS.  §    88. 

first  may  be  estimated  in  the  same  way ;  but  if  the  second  contains 
a  greater  quantity  of  ammonia,  the  first  must  be  measured,  and  an 
aliquot  part  taken  and  diluted  to  about  50  c.c.  with  water  free  from 
ammonia,  as  it  is  likely  to  contain  so  much  ammonia  as  to  give 
a  colour  too  intense  to  admit  of  easy  comparison.  A  colour  produced 
by  more  than  2  c.c.  of  ammonic  chloride  cannot  be  conveniently 
employed.'55'  When,  as  in  the  case  of  sewage,  a  large  quantity  of 
ammonia  is  known  to  be  present,  it  saves  trouble  to  distil  about 
100  c.c.  at  first,  and  at  once  take  an  aliquot  part  of  that,  as  above 
described.  If  the  liquid  spirts  in  distilling,  arrange  the  retort  so 
that  the  joint  between  the  retort  and  condenser  is  the  highest  point ; 
the  distillation  will,  proceed  rather  more  slowly,  but  anything 
carried  up  mechanically  will  be  returned  to  the  retort.  When  the 
ammonia  has  been  estimated  in  all  the  distillates,  add  together  the 
corresponding  volumes  of  ammonic  chloride  solution ;  then,  if  500 
c.c.  have  been  employed  for  the  experiment,  the  number  of  c.c.  of 
ammonic  chloride  used  divided  by  100  will  give  the  quantity  of 
nitrogen  as  ammonia  in  100,000  parts  of  the  water;  if  less  than 
that,  say  y  c.c.  have  been  used,  multiply  the  volume  of  ammonic 
chloride  by  5  and  divide  by  y. 

Before  commencing  this  operation,  ascertain  that  the  retort  and 
condenser  are  free  from  ammonia  by  distilling  a  little  common 
water  or  distilled  water  with  sodic  carbonate  until  the  distillate  is 
free  from  ammonia.  Remove  the  residue  then,  and  after  each 
estimation,  by  means  of  a  glass  syphon,  without  disconnecting  the 
retort.  If  a  small  quantity  of  water  is  to  be  distilled,  the  residue 
or  part  of  it  from  a  previous  experiment  may  be  left  in  the  retort, 
instead  of  adding  water  free  from  ammonia,  care  being  taken  that 
the  previous  distillation  was  continued  until  ammonia  ceased  to  be 
evolved. 

When  urea  is  present  the  evolution  of  ammonia  is  long  continued, 
owing  to  the  decomposition  of  the  urea.  In  such  cases,  collect  the 
distillate  in  smaller  quantities,  and  as  soon  as  the  first  rapid 
diminution  in  the  amount  of  ammonia  has  ceased,  neglect  the 
remainder,  as  this  would  be  due  almost  wholly  to  decomposition  of 
the  urea. 

4.  Estimation  of  Organic  Carbon  and  Nitrogen. — This  should  be 
commenced  as  soon  as  the  nitrogen  as  ammonia  has  been  determined. 
If  that  is  less  than  0*05  part  per  100,000,  a  liter  should  be  used; 
if  more  than  0'05,  and  less  than  0'2,  half  a  liter ;  if  more  than 
0'2  and  less  than  1*0,  a  quarter  of  a  liter;  if  more  than  1*0, 
a  hundred  c.c.  or  less.  These  quantities  are  given  as  a  guide  in 
dealing  with  ordinary  waters  and  sewage,  but  subject  to  variation 
in  exceptional  cases.  A  quantity  which  is  too  large  should  be 

*  In  order  to  insure  absolute  accuracy  in  Nesslerizing  it  is  necessary  that  the  distillate 
should  be  of  the  same  temperature  as  the  standard  liquid  made  by  mixing  the  ammonic 
chloride  with  distilled  water.  Hazen  and  Clark  (Amcr.  Chem.  Jour.  xii.  425)  found 
that  the  water  Nesslerized  from  a  metal  condenser,  immediately  after  collection,  gave 
a  lower  figure  than  when  the  two  liquids  were  allowed  to  assume  the  same  temperature. 


§    88.  NATURAL   WATERS   AND   SEAVAGE.  385 

avoided  as  entailing  needless  trouble  in  evaporation,  and  an 
inconveniently  bulky  residue  and  resulting  gas.  If  it  is  to  be 
filtered  before  analysis,  the  same  precaution  as  to  filter  paper  must 
be  taken  as  for  estimation  of  nitrogen  as  ammonia,  the  same  filter 
being  generally  used. 

Having  measured  the  quantity  to  be  used,  add  to  it  in  a  capacious 
flask  15  c.c.  of  the  solution  of  sulphurous  acid  (B.  /3),  and  boil 
briskly  for  a  few  seconds,  in  order  to  decompose  the  carbonates 
present.  Evaporate  to  dryness  in  a  hemispherical  glass  dish,  about 
a  decimeter  in  diameter,  and  preferably  without  a  lip,  supported  in 
a  copper  dish  with  a  flange  (fig.  46  d  e).  The  flange  has  a  diameter 
of  about  14  centimeters,  is  sloped  slightly  towards  the  centre,  and 
has  a  rim  of  about  5  m.m.  turned  up  on  its  edge,  except  at  one 
point,  where  a  small  lip  is  provided.  The  concave  portion  is  made 
to  fit  the  contour  of  the  outside  of  the  glass  dishes,  and  is  of  such 
a  depth  as  to  allow  the  edge  of  the  dish  to  rise  about  15  m.m. 
above  the  flange.  The  diameter  of  the  concavity  at  /  is  about 
90  m.m.,  and  the  depth  at  g  about  30  m.m.  A  thin  glass  shade, 
such  as  is  used  to  protect  statuettes,  about  30  centimeters  high, 
stands  on  the  flange  of  the  copper  dish,  its  diameter  being  such  as 
to  fit  without  difficulty  on  the  flange,  and  leave  a  sufficient  space 
between  its  interior  surface  and  the  edge  of  the  glass  dish.  The 
copper  dish  is  supported  on  a  steam  or  water  bath,  and  the  water 
as  it  evaporates  is  condensed  on  the  interior  of  the  glass  shade,  runs 
down  into  the  copper  dish,  filling  the  space  between  it  and  the 
glass  dish,  and  then  passes  off  by  the  lip  at  the  edge  of  the  flange, 
a  piece  of  tape  held  by  the  edge  of  the  glass  shade,  and  hanging 
over  the  lip,  guiding  it  into  a  vessel  placed  to  receive  it. 

We  are  indebted  to  Bischof  for  an  improved  apparatus  for 
evaporation,  which  by  keeping  the  dish  always  full  by  a  self-acting 
contrivance,  permits  the  operation  to  proceed  without  attention 
during  the  night,  and  thus  greatly  reduces  the  time  required. 
This  form  of  apparatus  is  shown  in  fig.  46.  The  glass  dish  d  is 
supported  by  a  copper  dish  e  as  described  above,  and  resting  on 
the  latter  is  a  stout  copper  ring  li  which  is  slightly  conical,  being 
115  m.m.  in  diameter  at  the  top  and  130  at  the  bottom.  At  the  top 
is  a  narrow  flange  of  about  10  m.m.  with  a  vertical  rim  of  about 
5  m.m.  The  diameter  across  this  flange  is  the  same  as  the  diameter 
of  the  dish  e,  so  that  the  glass  shade  i  will  fit  securely  either  on  li 
or  e.  The  height  of  the  conical  ring  is  about  80  m.m. 

The  automatic  supply  is  accomplished  on  the  well-known  prin- 
ciple of  the  bird  fountain,  by  means  of  a  delivery  tube  l>,  the  upper 
end  of  which  is  enlarged  to  receive  the  neck  of  the  flask  a  con- 
taining the  water  to  be  evaporated,  the  joint  being  carefully  ground 
so  as  to  be  water-tight.  The  upper  vertical  part  of  b,  including 
this  enlargement,  is  about  80  m.m.  in  length,  and  the  sloping  part 
about  260  m.m.  with  a  diameter  of  13  m.m.  The  lower  end 
which  goes  into  the  dish  is  again  vertical  for  about  85  m.m.,  and 

c  c 


S86 


VOLUMETRIC  ANALYSIS. 


carries  a  side  tube  c  of  about  3  m.m.  internal  diameter,  by  which 
air  enters  the  delivery  tube  whenever  the  level  of  the  water  in  the 
dish  falls  below  the  point  at  which  the  side  tube  joins  the  delivery 
tube.  The  distance  from  this  point  to  the  end  of  the  tube  which 
rests  on  the  bottom  of  the  dish  at  #,  and  is  there  somewhat  con- 
stricted, is  about  30  m.m.  The  side  tube  c  should  not  be  attached 
on  the  side  next  the  flask,  as  if  so  the  inclined  part  of  I)  passes 
over  its  mouth  and  renders  it  very  difficult  to  clean.  Mills 


Fig.  47. 


Tig.  4G. 


prevents  circulation  of  liquid  in  the  sloping  part  of  the  tube  by 
bending  it  into  a  slightly  undulating  form,  so  that  permanent 
bubbles  of  air  are  caught  and  detained  at  two  points  in  it.  The 
flask  a  should  hold  about  1200  c.c.  and  have  a  rather  narrow  neck 
— about  20  m.m. — and  a  flat  bottom.  A  small  slot  is  cut  in  the 
upper  edge  of  the  copper  ring  h  to  accommodate  the  delivery  tube, 
as  shown  in  fig.  47.  Its  size  and  shape  should  be  such  that  the 
tube  does  not  touch  the  edge  of  the  glass  shade  it  lest  water 


§    88.  NATURAL   WATERS  AND   SEWAGE.  387 

running  down  the  inner  surface  of  the  shade  should  find  its  way 
down  the  outside  of  the  delivery  tube  into  the  dish.  This  being 
avoided,  the  opening  should  be  as  closely  adjusted  to  the  size  of  the 
delivery  tube  as  can  be.  The  copper  dish  e  should  rest  on  a  steam 
or  water  bath,  so  that  only  the  spherical  part  is  exposed  to  the 
heal 

After  the  addition  of  the  15  c.c.  of  sulphuric  acid,  the  water 
may  either  be  boiled  in  the  flask  a,  or  in  another  more  capacious 
one,  and  then  transferred  to  a.  It  should  be  allowed  to  cool 
before  the  delivery  tube  is  adjusted,  otherwise  the  joint  between 
the  two  is  liable  to  become  loose  by  expansion  of  the  cold  socket 
of  the  delivery  tube,  after  being  placed  over  the  hot  neck  of 
the  flask. 

The  glass  dish  having  been  placed  on  the  copper  dish  e,  the 
conical  ring  li  is  fitted  on,  and  the  flask  with  the  delivery  tube 
attached  inverted,  as  shown  in.  fig.  46,  «,  b.  This  should  not  be 
done  too  hurriedly,  and  with  a  little  care  there  is  no  risk  of  loss. 
The  flask  is  supported  either  by  a  large  wooden  filtering  stand,  the 
ring  of  which  has  had  a  slot  cut  in  it  to  allow  the  neck  of  the  flask 
to  pass,  or  by  a  clamp  applied  to  the  upper  end  of  the  delivery 
tube  where  the  neck  of  the  flask  fits  in.  The  delivery  tube  having 
been  placed  in  the  slot  made  to  receive  it,  the  glass  shade  is  fitted 
on,  and  the  evaporation  allowed  to  proceed.  When  all  the  water 
has  passed  from  the  flask  into  the  dish,  the  flask  and  delivery  tube, 
and  the  conical  ring  h  may  be  removed,  and  the  glass  shade  placed 
directly  on  the  dish  e  until  the  evaporation  is  complete.  If  the 
water  is  expected  to  contain  a  large  quantity  of  nitrates,  two  or 
three  drops  of  chloride  of  iron  (B.  £)  should  be  added  to  the  first 
dishful;  and  if  it  contains  little  or  no  carbonate,  one  or  two  c.c. 
of  hydric  sodic  sulphite  (B.  y).  The  former  facilitates  the  destruc- 
tion of  nitrates  and  nitrites,  and  the  latter  furnishes  base  for  the 
sulphuric  acid  produced  by  oxidation  of  the  sulphurous  acid,  and 
which  would,  if  free,  decompose  the  organic  matter  when  concen- 
trated by  evaporation.  An  estimate  of  the  quantity  of  carbonate 
present,  sufficiently  accurate  for  this  purpose,  may  generally  be 
made  by  observing  the  quantity  of  precipitate  thrown  down  on 
addition  of  sodic  carbonate  in  the  determination  of  nitrogen  as 
ammonia. 

With  sewages  and  very  impure  waters  (containing  upwards  of  0*1 
part  of  nitrogen  as  ammonia  per  100,000  for  example)  such  great 
precaution  is  hardly  necessary,  and  the  quantity  to  evaporate  being 
small,  the  evaporation  may  be  conducted  in  a  glass  dish  placed 
directly  over  a  steam  bath,  and  covered  with  a  drum  or  disc  of  filter 
paper  made  by  stretching  the  paper  by  means  of  two  hoops  of  light 
split  cane,  one  thrust  into  the  other,  the  paper  being  between  them, 
in  the  Avay  often  employed  in  making  dialysers.  This  protects  the 
contents  of  the  dish  from  dust,  and  also,  to  a  great  extent,  from 
ammonia  which  may  be  in  the  atmosphere,  and  which  would  impair 

c  c  2 


388  VOLUMETRIC  ANALYSIS.  §    88. 

the  accuracy  of  the  results.  As  a  glass  dish  would  be  in  some  danger 
of  breaking  by  the  introduction  of  cold  water,  the  flask  containing 
the  water  being  evaporated  in  this  or  in  the  first  described  manner, 
must  be  kept  on  a  hot  plate  or  sand  bath  at  a  temperature  of  about 
60°  or  70°  C.,  and  should  be  covered  with  a  watch-glass.  This 
precaution  is  not  necessary  when  Bischof's  apparatus  is  used. 
If,  at  any  time,  the  water  in  the  flask  ceases  to  smell  strongly  of 
sulphurous  acid,  more  should  be  added.  The  preliminary  boiling 
may  be  omitted  when  less  than  250  c.c.  is  used.  When  the 
nitrogen  as  nitrates  and  nitrites  exceeds  0'5  part,  the  dish,  after 
the  evaporation  has  been  carried  to  dryness,  should  be  filled  with 
distilled  water  containing  ten  per  cent,  of  saturated  sulphurous 
acid  solution,  and  the  evaporation  again  carried  to  dryness.  If  it 
exceeds  I'O  part,  a  quarter  of  a  liter  of  this  solution  should  be 
evaporated  on  the  residue;  if  2*0  parts,  half  a  liter;  and  if  5  parts, 
a  liter.  If  less  than  a  liter  has  been  evaporated,  a  proportionally 
smaller  volume  of  this  solution  may  be  used.  The  estimation  of 
nitrogen  as  nitrates  and  nitrites  will  usually  be  accomplished  before 
this  stage  of  the  evaporation  is  reached. 

M.  W.  Williams  proposes  to  avoid  the  use  of  sulphurous  acid, 
with  its  acknowledged  disadvantages  and  defects,  by  removing 
the  nitric  and  nitrous  acids  with  the  zinc-copper  couple  and 
converting  them  into  ammonia.  If  the  amount  is  large,  it  is  best 
distilled  from  a  retort  into  weak  acid;  if  small,  into  an  empty 
Messier  tube.  The  amount  so  found  is  calculated  into  nitrogen 
as  nitrates  and  nitrites,  if  the  latter  are  found  in  the  water.  The 
residue,  when  free  from  ammonia  is  further  concentrated,  the 
separated  carbonates  re-dissolved  in  phosphoric  or  sulphurous 
acid,  in  just  sufficient  quantity,  then  transferred  to  a  glass 
basin  for  evaporation  to  dryness  as  usual  ready  for  combustion 
(/.  C.  S.  1881,  144). 

In  the  case  of  sewage,  however,  it  is  advisable  to  employ  hydric 
metaphosphate  in  the  place  of  sulphurous  acid,  as  the  ammonic 
phosphate  is  even  less  volatile  than  the  sulphite.  This  can  only 
be  employed  for  sewage  and  similar  liquids,  which  are  free  from 
nitrates  and  nitrites.  To  the  measured  quantity  of  liquid  to  be 
evaporated  add,  in  the  glass  dish,  10  c.c.  of  the  hydric  metaphos- 
phate (B.  fj,),  and,  in  order  to  render  the  residue  more  convenient 
to  detach  from  the  dish,  about  half  a  gram  of  calcic  phosphate 
(B.  v),  and  proceed  as  usual.  No  chloride  of  iron,  sulphurous 
acid,  or  sodic  sulphite  is  required;  nor  is  it  necessary  to  boil 
before  commencing  the  evaporation. 

The  next  operation  is  the  combustion  of  the  residue.  The 
combustion  tube  should  be  of  hard,  difficultly  fusible  glass,  with 
an  internal  diameter  of  about  10  m.m.  Cut  it  in  lengths  of  about 
430  m.m.,  and  heat  one  end  of  each  in  the  blowpipe  flame  to  round 
the  edge.  Wash  well  'with  water,  brushing  the  interior  carefully 
a  tube  brush  introduced  at  the  end  whose  edge  has  been 


§    88.  NATURAL  WATERS   AND   SEWAGE.  389 

rounded,  rinse  with  distilled  water,  and  dry  in  an  oven.  When 
dry,  draw  off  and  close,  at  the .  blowpipe,  the  end  whose  edge  has 
been  left  sharp.  The  tube  is  then  ready  for  use. 

Pour  on  to  the  perfectly  dry  residue  in  the  glass  dish,  standing 
on  a  sheet  of  white  glazed  paper,  a  little  of  the  fine  cupric  oxide 
(B.  «),  and  with  the  aid  of  a  small  elastic  steel  spatula  (about  100 
in.m.  long  and  15  m.m.  wide)  carefully  detach  the  residue  from  the 
glass  and  rub  it  down  with  the  cupric  oxide.  The  spatula  readily 
accommodates  itself  to  the  curvature  of  the  dish,  and  effectually 
scrapes  its  surface.  When  the  contents  of  the  dish  are  fairly 
mixed,  fill  about  30  m.m.  of  the  length  of  the  combustion  tube 
with  granulated  cupric  oxide  (B.  c),  and  transfer  the  mixture  in  the 
dish  to  the  tube.  This  is  done  in  the  usual  way  by  a  scooping 
motion  of  the  end  of  the  tube  in  the  dish,  the  last  portions  being 
transferred  by  the  help  of  a  bent  card  or  a  piece  of  clean  and  smooth 
platinum  foil.  Rinse  the  dish  twice  with  a  little  fine  cupric  oxide, 
rubbing  it  well  round  each  time  with  the  spatula,  and  transfer  to 
the  tube  as  before.  Any  particles  scattered  on  the  paper  are  also 
to  be  put  in.  Fill  up  to  a  distance  of  270  m.m.  from  the  closed 
end  with  granular  cupric  oxide,  put  in  a  cylinder  of  metallic  copper 
(B.  £),  and  then  again  20  m.m.  of  granular  cupric  oxide.  This  last 
is  to  oxidize  any  traces  of  carbonic  oxide  which  might  be  formed 
from  carbonic  anhydride  by  the  reducing  action  of  iron  or  other 
impurity  in  the  metallic  copper.  Now  draw  out  the  end  of  the 
tube  so  as  to  form  a  neck  about  100  m.m.  long  and  4  m.m.  in 
diameter,  fuse  the  end  of  this  to  avoid  injury  to  the  india-rubber 
connector,  and  bend  it  at  right  angles.  It  is  now  ready  to  be 
placed  in  the  combustion  furnace  and  attached  to  the  Sprengel 
pump. 

The  most  convenient  form  of  this  instrument  for  the  purpose  is 
shown  in  fig.  48.  The  glass  funnel  a  is  kept  supplied  with  mercury, 
and  is  connected  by  a  caoutchouc  joint  with  a  long  narrow  glass 
tube  which  passes  down  nearly  to  the  bottom  of  a  wider  tube  d, 
900  iii.m.  long,  and  10  m.m.  in  internal  diameter.  The  upper  end 
of  d  is  cemented  into  the  throat  of  a  glass  funnel  e  from  which 
the  neck  has  been  removed.  A  screw  clamp  ?;  regulates  the  flow  of 
mercury  down  the  narrow  tube.  A  piece  of  ordinary  glass  tube  /  g, 
about  6  m.m.  in  diameter  and  600  m.m.  in  length,  is  attached  at  cj 
to  a  tube  <j  li  k,  about  6  m.m.  in  diameter,  1500  m.m.  long,  with  a 
bore  of  1  m.m.  This  is  bent  sharply  on  itself  at  7i,  the  part  h  k 
being  1300  m.m.  long,  and  the  two  limbs 'are  firmly  lashed  together 
with  copper  wire  at  two  points,  the  tubes  being  preserved  from 
injury  by  short  sheaths  of  caoutchouc  tube.  The  end  k  is  recurved 
for  the  delivery  of  gas.  At  the  top  of  the  bend  at  7i,  a  piece  of 
ordinary  tube  h  Z,  about  120  m.m.  long,  and  5  m.m.  in  diameter,  is 
sealed  on.  The  whole  I  k  is  kept  in  a  vertical  position  by  a  loose 
support  or  guide,  near  its  upper  part,  the  whole  of  its  weight  resting 
on  the  end  A*,  so  that  it  is  comparatively  free  to  move.  It  is 


390 


VOLUMETRIC   ANALYSIS. 


§  88. 


connected  at/  with  the  lower  end  of  d,  by  means  of  a  piece  of  caout- 
chouc tube  covered  with  tape,  and  furnished  with  a  screw  clamp  e. 
At  I  it  is  connected  with  the  combustion  tube  o,  by  the  connecting 


Pig.  48. 

tube  I  m  n,  which  is  made  of  tube  similar  to  that  used  for  h  It.  A 
cork  slides  on  li  I,  which  is  fitted  into  the  lower  end  of  a  short 
piece  of  tube  of  a  width  sufficient  to  pass  easily  over  the  caoutchouc 


§    88.  NATUKAL  WATERS  AND  SEWAGE.  391 

joint  connecting  the  tubes  at  I,  After  the  joint  has  been  arranged 
(the  ends  of  the  tubes  just  touching)  and  bound  with  wire,  the 
cork  and  wide  tube  are  pushed  over  it  and  filled  with  glycerine. 
The  joint  at  n  is  of  exactly  the  same  kind,  but  as  it  has  to  be  fre- 
quently disconnected,  water  is  used  instead  of  glycerine,  and  the 
caoutchouc  is  not  bound  on  to  the  combustion  tube  with  wire.  It 
will  be  seen  that  the  joint  at  I  is  introduced  chiefly  to  give  flexi- 
bility to  the  apparatus.  At  in  is  a  small  bulb  blown  on  the  tube 
for  the  purpose  of  receiving  water  produced  in  the  combustion. 
This  is  immersed  in  a  small  water  trough  x.  The  tube  li  k  stands  in 
a  mercury  trough  p,  which  is  shown  in  plan  on  a  larger  scale  at  B. 

This  trough  should  be  cut  out  of  a  solid  piece  of  mahogany,  as  it 
is  extremely  difficult  to  make  joints  to  resist  the  pressure  of  such  a 
depth  of  mercury.  It  is  200  m.m.  long,  155  m.m.  wide,  and  100 
m.m.  deep,  outside  measurement.  The  edge  r  r  is  13  m.m.  wide, 
and  the  shelf  s  65  m.m.  wide,  174  m.m.  long,  and  50  m.m.  deep 
from  the  top  of  the  trough.  The  channel  t  is  25  m.m.  wide,  and 
75  m.m.  deep,  having  at  one  end  a  circular  well  w,  42  m.m.  in 
diameter,  and  90  m.m.  deep.  The  recesses  u  u  are  to  receive  the 
ends  of  two  Sprengel  pumps.  They  are  each  40  m.m.  long,  25  m.m. 
wide,  and  of  the  same  depth  as  the  channel  t.  A  short  iron  wire  v, 
turning  on  a  small  staple,  and  resting  at  the  other  end  against  an 
iron  pin,  stretches  across  each  of  these,  and  serves  as  a  kind 
of  gate  to  support  the  test  tube,  in  which  the  gas  delivered 
by  the  pump  is  collected.  The  trough  stands  upon  four  legs, 
75  m.m.  high,  and  is  provided  at  the  side  with  a  tube  and  screw 
clamp  q,  by  which  the  mercury  may  be '  drawn  off  to  the  level  of 
the  shelf  s. 

The  combustion  tube  being  placed  in  the  furnace,  protected  from 
the  direct  action  of  the  flame  by  a  sheet-iron  trough  lined  with 
asbestos,  and  the  water  joint  at  n  adjusted,  the  gas  is  lighted  at 
the  front  part  of  furnace  so  as  to  heat  the  whole  of  the  metallic 
copper  and  part  of  the  cupric  oxide.  A  small  screen  of  sheet 
iron  is  adjusted  astride  of  the  combustion  tube  to  protect  the 
part  beyond  the  point  up  to  which  the  gas  is  burning  from  the 
heat. 

At  the  same  time  a  stream  of  mercury  is  allowed  to  flow  from  the 
funnel  a,  which  fills  the  tubes  d  and  /  until  it  reaches  li,  when  it 
falls  in  a  series  of  pellets  down  the  narrow  tube  li  k,  each  carrying 
before  it  a  quantity  of  air  drawn  from  the  combustion  tube.  The 
flow  of  mercury  must  be  controlled  by  means  of  the  clamps  b  and  e, 
so  as  not  to  be  too  rapid  to  admit  of  the  formation  of  these  separate 
pistons,  and  especially,  care  should  be  taken  not  to  permit  it  to  go 
so  fast  as  to  mount  into  the  connecting  tube  I  in  n,  as  it  cannot  be 
removed  thence  except  by  disconnecting  the  tube.  During  the 
exhaustion,  the  trough  x  is  filled  with  hot  water  to  expel  from  the 
bulb  m  any  water  condensed  from  a  previous  operation.  In  about 
ten  minutes  the  mercury  will  fall  in  the  tube  li  7c  with  a  loud,  sharp, 


392 


VOLUMETRIC  ANALYSIS. 


§    88. 


clicking  sound,  showing  that  the  vacuum  is  complete.  As  soon  as 
this  occurs,  the  pump  may  be  stopped,  a  test  tube  filled  with  mercury 
inverted  over  the  delivery  end  of  the  tube  £,  cold  water  substituted 


Pig.  49. 

for  hot  in  the  trough  x,  the  iron  screen  removed,  and  combustion 
proceeded  with  in  the  usual  way.  This  will  take  from  fifty  to  sixty 
minutes.  As  soon  as  the  whole  of  the  tube  is  heated  to  redness,  the 


§    88.  NATURAL  WATERS  AND   SEWAGE.  393 

gas  is  turned  off,  and  the  tube  immediately  exhausted,  the  gases 
produced  being  transferred  to  the  tube  placed  to  receive  them. 
When  the  exhaustion  is  complete,  the  test  tube  of  gas  may  be 
removed  in  a  small  beaker,  and  transferred  to  the  gas  analysis 
apparatus. 

This  gas  collected  consists  of  carbonic  anhydride,  nitric  oxide, 
nitrogen,  and  (very  rarely)  carbonic  oxide,  which  can  readily  be 
separated  and  estimated  by  the  ordinary  methods  of  gas  analysis. 
This  is  rapidly  accomplished  with  the  apparatus  described  in 
Part  VII.,  or  the  simpler  form,  shown  in  the  accompanying  diagram, 
which,  whilst  it  does  not  permit  of  analysis  by  explosion,  leaves 
nothing  to  be  desired  for  this  particular  operation.  It  is  essentially 
that  described  by  Frankland  (/.  C.  S.  [2]  vi.  109),  but  is 
slightly  modified  in  arrangement.  In  the  diagram,  a  c  d  is  a 
measuring  tube,  of  which  the  cylindrical  portion  a  is  370  m.m. 
long,  and  18  m.m.  in  internal  diameter,  the  part  c  40  m.m.  long, 
and  7  m.m.  in  diameter,  and  the  part  d  175  m.m.  long,  and  2*5  m.m. 
in  diameter.  To  the  upper  end  of  d  a  tube,  with  a  capillary  bore 
and  stop-cock  /,  is  attached,  and  bent  at  right  angles.  Allowing 
20  m.m.  for  each  of  the  conical  portions  at  the  joints  between  a 
and  c,  and  c  and  d,  and  25  m.m.  for  the  vertical  part  of  the  capillary 
tube,  the  vertical  measurement  of  the  entire  tube  is  650  m.m. 
It  is  graduated  carefully  from  below  upward,  at  intervals  of  10  m.m., 
the  zero  being  about  100  m.m.  from  the  end,  as  about  that  length 
of  it  is  hidden  by  its  support,  and  therefore  unavailable.  The 
topmost  10  m.m.  of  d  should  be  divided  into  single  millimeters. 
At  the  free  end  of  the  capillary  tube  a  small  steel  cap,  shown  in 
fig.  50,  B,  is  cemented  gas-tight.  The  lower  end  of  a  is  drawn  out 


\ 


Fig.  50. 

to  a  diameter  of  5  m.m.  The  tube  &  is  about  1*2  meter  long,  and 
6  m.ni.  internal  diameter,  is  drawn  out  like  a  at  the  lower  end,  and 
graduated  in  millimeters  from  below  upward,  the  zero  being  about 
100  m.m.  from  the  end.*  The  tubes  a  c  d  and  b  pass  through  a 
caoutchouc  stopper  o,  which  fits  into  the  lower  end  of  a  glass 
cylinder  n  n,  intended  to  contain  water  to  give  a  definite  tempera- 
ture to  the  gas  in  measuring.  The  zeros  of  the  graduations  should 
be  about  10  m.m.  above  this  stopper.  Immediately  below  this 
the  tubes  are  firmly  clasped  by  the  wooden  clamp  p  (shown  in  end 

*  The  graduation  is  not  shown  in  the  diagram. 


394 


VOLUMETRIC   ANALYSIS. 


§  88. 


elevation  and  plan  at  fig.  49  B,  C),  the  two  parts  of  which  are 
drawn  together  by  screws,  the  tubes  being  protected  from  injury  by 
a  piece  of  caoutchouc  tube  fitted  over  each.  The  clamp  is  supported 
on  an  upright  piece  of  wood,  screwed  firmly  to  the  base  A.  If  the 
stopper  o  is  carefully  fitted,  and  the  tubes  tightly  clamped,  no 
other  support  than  p  will  be  necessary.  The  tubes  below  the  clamp 
are  connected  by  joints  of  caoutchouc  covered  with  tape,  and 
strongly  bound  with  wire,  to  the  vertical  legs  of  the  union  piece  q, 
to  the  horizontal  leg  of  which  is  attached  a  long  caoutchouc  tube 
of  about  2  m.m,  internal  diameter,  which  passes  to  the  glass  reser- 
voir t.  This  tube  must  be  covered  with  strong  tape,  or  (less 
conveniently)  have  a  lining  of  canvas  between  two  layers  of  caout- 
chouc, as  it  will  be  exposed  to  considerable  pressure.  In  its  course 
it  passes  through  the  double  screw  steel  pinch-cock  r,  the  lower  bar 
of  which  is  fixed  to  the  side  of  the  clamp  p.  It  is  essential  that 
the  screws  of  the  pinch-cock  should  have  smooth  collars  like  that 
shown  in  fig.  50  A,  and  that  the  upper  surface  of  the  upper  bar 
of  the  pinch-cock  should  be  quite  flat,  the  surfaces  between  which 
the  tube  is  passed  being  cylindrical. 

Frankland  has  introduced  a  form  of  joint  by  which  the  steel 
caps  and  clamp  are  dispensed  with.  The  capillary  tube  at  the 
upper  end  of  a  c  d  is  expanded  into  a  small  cup  or  funnel,  and 
the  capillary  tube  of  the  laboratory  vessel  bent  twice  at  right 
angles,  the  end  being  drawn  out  in  a  conical  form  to  fit  into  the 
neck  of  the  above-named  cup.  The  opposed  surfaces  are  fitted 
by  grinding  or  by  covering  the  conical  end  of  the  laboratory 
vessel  with  thin  sheet  caoutchouc.  The  joint  is  kept  tight  by 
an  elastic  band  attached  at  one  end  to  the  stand,  and  at  the  other 
to  a  hook  on  the  horizontal  tube  of  the  laboratory  vessel,  and  the 
cup  is  filled  with  mercury. 

In  the  base  A  is  fixed  a  stout  iron  rod,  1*4  meter  long,  with 


Fig.  51.  Fig.  52. 

a  short  horizontal  arm  at  its  upper  end,  containing  two  grooved 
pulleys.  The  reservoir  t  is  suspended  by  a  cord  passing  over  these 
pulleys,  and  attached  to  an  eye  u  in  the  iron  rod,  the  length  of  the 
cord  being  such  that,  when  at  full  stretch,  the  bottom  of  the 
reservoir  is  level  with  the  bottom  of  the  clamp  p.  A  loop  is  made 
on  the  cord,  which  can  be  secured  by  a  hook  v  on  the  rod,  so  that 
when  thus  suspended,  the  bottom  of  t  is  about  100  m.m.  above  the 
stop-cock  /.  A  stout  elastic  band  fitted  round  t  at  its  largest 


§    88.  NATURAL  WATERS  AND   SEWAGE.  395 

diameter  acts  usefully  as  a  fender  to  protect  it  from  an  accidental 
blow  against  the  iron  rod.  A  thermometer  e,  suspended  by  a  wire 
hook  from  the  edge  of  the  cylinder  n  n,  gives  the  temperature  of 
the  contained  water,  the  uniformity  of  which  may  be  insured 
(though  it  is  scarcely  necessary)  by  passing  a  slow  succession  of 
bubbles  of  air  through  it,  or  by  moving  up  and  down  in  it  a  wire 
with  its  end  bent  into  the  form  of  a  ring.  The  jar  k  is  called  the 
laboratory  vessel,  and  is  100  in.m.  high,  and  38  in.m.  in  internal 
diameter,  having  a  capillary  tube,  glass  stop-cock,  and  steel  cap  g'  h 
exactly  like  /  y.  The  mercury  trough  I  is  shown  in  figs.  51  and 
52.  It  is  of  solid  mahogany,  265  m.m.  long,  80  m.m.  broad,  and 
90  m.m.  deep,  outside  measurement.  The  rim  a  a  a  a  is  8  m.m. 
broad,  and  15  m.m.  deep.  The  excavation  b  is  230  m.m.  long, 
26  m.m.  broad,  and  65  m.m.  deep,  with  a  circular  cavity  to  receive 
the  laboratory  vessel  sunk  at  one  end,  45  m.m.  in  diameter,  and 
20  m.m.  in  depth  below  the  top  of  the  excavation.  Two  small 
lateral  indentations  c  c  (fig.  52)  near  the  other  end  accommodate 
a  capsule  for  transferring  to  the  trough  tubes  containing  gas.  This 
trough  rests  upon  a  telescope  table,  which  can  be  fixed  at  any 
height  by  means  of  a  screw,  and  is  supported  on  three  feet.  It 
must  be  arranged,  so  that  when  the  laboratory  vessel  is  in  its  place 
in  the  trough,  the  two  steel  caps  exactly  correspond  face  to  face. 

The  difference  of  level  of  the  mercury  in  the  tubes  b  and  a  c  d, 
caused  by  capillary  action,  when  both  are  freely  open  to  the  air, 
must  be  ascertained  by  taking  several  careful  observations.  This 
will  be  different  for  each  of  the  portions  a  c  and  d,  and  must  be 
added  to  or  deducted  from  the  observed  pressure,  as  the  mercury 
when  thus  freely  exposed  in  both  tubes  to  the  atmospheric  pressure 
stands  in  a  c  or  d  above  or  below  that  in  6.  This  correction  will 
include  also  any  that  may  be  necessary  for  difference  of  level  of 
the  zeros  of  the  graduations  of  the  two  tubes,  and,  if  the  relative 
positions  of  these  be  altered,  it  must  be  redetermined.  A  small 
telescope,  sliding  on  a  vertical  rod,  should  be  used  in  these  and  all 
other  readings  of  the  level  of  mercury. 

The  capacity  of  the  measuring  tube  a  c  d  at  each  graduation 
must  now  be  determined.  This  is  readily  done  by  first  filling  the 
whole  apparatus  with  mercury,  so  that  it  drips  from  the  cap  y. 
The  stop-cock  /  is  then  closed,  a  piece  of  caoutchouc  tube  slipped 
over  the  cap,  and  attached  to  a  funnel  supplied  with  distilled 
water.  The  reservoir  t  being  lowered,  the  clamp  r  and  the  stop- 
cock /  are  opened,  so  that  the  mercury  returns  to  the  reservoir, 
water  entering  through  the  capillary  tube.  As  soon  as  it  is  below 
the  zero  of  the  graduation,  the  stop-cock  /  is  closed,  the  funnel  and 
caoutchouc  tube  removed  from  the  cap,  and  the  face  of  the  last 
slightly  greased  in  order  that  water  may  pass  over  it  without 
adhering.  Kow  raise  the  reservoir,  open  the  stop-cock  /,  and  allow 
the  water  to  flow  gently  out  until  the  top  of  the  convex  surface  of 
the  mercury  in  a  just  coincides  with  the  zero  of  the  graduation. 


396  VOLUMETRIC.  ANALYSIS.  §    88. 

The  mercury  should  be  controlled  by  the  clamp  r,  so  that  the  water 
issues  under  very  slight  pressure.  Note  the  temperature  of  the 
water  in  the  water-jacket,  and  proceed  with  the  expulsion  of  the 
water,  collecting  it  as  it  drops  from  the  steel  cap  in  a  small  carefully 
weighed  glass  flask.  When  the  mercury  has  risen  through  100  m.m. 
stop  the  flow  of  water,  and  weigh  the  flask.  The  Aveight  of  water 
which  was  contained  between  the  graduations  0  and  100  on  the 
tube  is  then  known,  and  if  the  temperature  be  4°  C.,  the  weight  in 
grams  will  express  the  capacity  of  that  part  of  the  tube  in  cubic 
centimeters.  If  the  temperature  be  other  than  4°  C.,  the  volume 
must  be  calculated  by  the  aid  of  the  co-efficient  of  expansion  of 
water  by  heat.  In  a  similar  way  the  capacity  of  the  tube  at 
successive  graduations  about  100  m.m.  apart  is  ascertained,  the 
last  determination  in  a  being  at  the  highest,  and  the  first  in  c  at 
the  lowest  graduation  on  the  cylindrical  part  of  each  tube ;  the 
tube  between  these  points  and  similar  points  011  c  and  d  being 
so  distorted  by  the  glass  blower  that  observations  could  not  well 
be  made.  The  capacity  at  a  sufficient  number  of  points  being 
ascertained,  that  at  each  of  the  intermediate  graduations  may  be 
calculated,  and  a  table  arranged  with  the  capacity  marked  against 
each  graduation.  As  the  calculations  in  the  analysis  are  made  by 
the  aid  of  logarithms,  it  is  convenient  to  enter  on  this  table  the 
logarithms  of  the  capacities  instead  of  the  natural  numbers. 

In  using  the  apparatus,  the  stop-cocks  on  the  measuring  tube 
and  laboratory  vessel  should  be  slightly  greased  with  a  mixture  of 
resin  cerate  and  oil,  or  vaseline,  the  whole  apparatus  carefully  filled 
with  mercury,  and  the  stop-cock/closed;  next  place  the  laboratory 
vessel  in  position  in  the  mercury  trough,  and  suck  out  the  air. 
This  is  readily  and  rapidly  done  by  the  aid  of  a  short  piece  of 
caoutchouc  tube,  placed  in  the  vessel  just  before  it  is  put  into  the 
mercury  trough,  and  drawn  away  as  soon  as  the  air  is  removed. 
Suck  out  any  small  bubbles  of  air  still  left  through  the  capillary 
tube,  and  as  soon  as  the  vessel  is  entirely  free  from  air  close  the 
stop-cock.  Slightly  grease  the  faces  of  both  caps  with  resin  cerate 
(to  which  a  little  oil  should  be  added  if  very  stiff),  and  clamp  them 
tightly  together.  On  opening  both  stop-cocks  mercury  should  flow 
freely  through  the  capillary  communication  thus  formed,  and  the 
whole  should  be  quite  free  from  air.  To  ascertain  if  the  joints  are 
all  in  good  order,  close  the  stop-cock  /*,  and  lower  the  reservoir  t  to 
its  lowest  position ;  the  joints  and  stop-cocks  will  thus  be  subjected 
to  a  pressure  of  nearly  half  an  atmosphere,  and  any  leakage  would 
speedily  be  detected.  If  all  be  right,  restore  the  reservoir  to  its 
upper  position. 

Transfer  the  tube  containing  the  gas  to  be  analyzed  to  an 
ordinary  porcelain  mercury  trough ;  exchange  the  beaker  in  which 
it  has  been  standing  for  a  small  porcelain  capsule,  and  transfer  it 
to  the  mercury  trough  ?,  the  capsule  finding  ample  room  where  the 
trough  is  widened  by  the  recess  D. 


§    88.  NATURAL  WATERS  AND   SEWAGE.  897 

Carefully  decant  the  gas  to  the  laboratory  vessel,  and  add  a  drop 
or  two  of  potassic  bichromate  solution  (B.  77)  from  a  small  pipette 
with  a  bent  capillary  delivery  tube,  to  ascertain  if  the  gas  contains 
any  sulphurous  anhydride.  If  so,  the  yellow  solution  will 
immediately  become  green  from  the  formation  of  a  chromic  salt, 
and  the  gas  must  be  allowed  to  stand  over  the  eliminate  for  four  or 
five  minutes,  a  little  more  of  the  solution  being  added  if  necessary. 
The  absorption  may  be  greatly  accelerated  by  gently  shaking  from 
time  to  time  the  stand  on  which  the  mercury  trough  rests,  so  as  to 
cause  the  solution  to  wet  the  sides  of  the  vessel.  With  care  this 
may  be  done  without  danger  to  the  apparatus.  Mercury  should  be 
allowed  to  pass  slowly  into  the  laboratory  vessel  during  the  whole 
time,  as  the  drops  falling  tend  to  maintain  a  circulation  both  in 
the  gas  and  in  the  absorbing  liquid.  The  absence  of  sulphurous 
anhydride  being  ascertained,  both  stop-cocks  are  set  fully  open,  the 
reservoir  t  lowered,  and  the  gas  transferred  to  the  measuring  tube. 
The  stop-cock  li  should  be  closed  as  soon  as  the  liquid  from  the 
laboratory  vessel  is  within  about  10  m.m.  of  it.  The  bore  of  the 
capillary  tube  is  so  fine,  that  the  quantity  of  gas  contained  in  it  is 
too  small  to  affect  the  result.  Next  bring  the  top  of  the  meniscus 
of  mercury  seen  through  the  telescope  exactly  to  coincide  with  one 
of  the  graduations  on  the  measuring  tube,  the  passage  of  mercury 
to  or  from  the  reservoir  being  readily  controlled  by  the  pinch-cock  r. 
Note  the  position  of  the  mercury  in  the  measuring  tube  and  in  the 
pressure  tube  b,  the  temperature  of  the  water-jacket,  and  the  height 
of  the  barometer,  the  level  of  the  mercury  in  the  pressure  tube  and 
barometer  being  read  to  the  tenth  of  a  m.m.  and  the  thermometer 
to  0*1°  C.  This  done,  introduce  into  the  laboratory  vessel  from 
a  pipette  with  a  bent  point,  a  few  drops  of  potassic  hydrate  solution 
(B.  0),  and  return  the  gas  to  the  laboratory  vessel.  The  absorption 
of  carbonic  anhydride  will  be  complete  in  about  three  to  five 
minutes,  and  if  the  volume  of  the  gas  is  large,  may  be  much 
accelerated  by  gently  shaking  the  stand  from  time  to  time,  so  as  to 
throw  up  the  liquid  on  the  sides  of  the  vessel.  If  the  small 
pipettes  used  to  introduce  the  various  solutions  are  removed  from 
the  mercury  trough  gently,  they  will  always  contain  a  little  mercury 
in  the  bend,  which  will  suffice  to  keep  the  solution  from  flowing 
out,  and  they  may  be  kept  in  readiness  for  use  standing  upright  in 
glass  cylinders  or  other  convenient  supports.  At  the  end  of  five 
minutes  the  gas,  which  now  consists  of  nitrogen  and  nitric  oxide, 
is  again  transferred  to  the  measuring  tube,  and  the  operation  of 
measuring  repeated ;  the  barometer,  however,  need  not  be  observed, 
under  ordinary  circumstances,  more  than  once  for  each  analysis, 
as  the  atmospheric  pressure  will  not  materially  vary  during  the 
twenty-five  to  thirty  minutes  required.  Next  pass  into  the 
laboratory  vessel  a  few  drops  of  saturated  solution  of  pyrogallic 
acid  (  B.  t),  and  return  the  gas  upon  it.  The  object  of  adding  the 
pyrogallic  acid  at  this  stage  is  to  ascertain  if  oxygen  is  present,  as 


398  VOLUMETRIC   ANALYSIS.  §    88. 

sometimes  happens  when  the  total  quantity  of  gas  is  very  small, 
and  the  vacuum  during  the  combustion  but  slightly  impaired. 
Under  such  circumstances,  traces  of  oxygen  are  given  off  by  the 
cupric  oxide,  and  pass  so  rapidly  over  the  metallic  copper,  as  to 
escape  absorption.  This  necessarily  involves  the  loss  of  any  nitric 
oxide  which  also  escapes  the  copper,  but  this  is  such  a  very  small 
proportion  of  an  already  small  quantity  that  its  loss  will  not 
appreciably  affect  the  result.  If  oxygen  be  present,  allow  the  gas 
to  remain  exposed  to  the  action  of  the  pyrogallate  until  the  liquid 
when  thrown  up  the  sides  of  the  laboratory  vessel  runs  off  without 
leaving  a  dark  red  stain.  If  oxygen  be  not  present,  a  few  bubbles 
of  that  gas  (B.  X)  are  introduced  to  oxidize  the  nitric  oxide  to 
pernitric  oxide,  which  is  absorbed  by  the  potassic  hydrate.  The 
oxygen  may  be  very  conveniently  added  from  the  gas  pipette  shown 

in  fig.  53,  where  a  I  are  glass 
bulbs  of  about  50  m.m.  dia- 
meter, connected  by  a  glass 
tube,  the  bore  of  which  is 
constricted  at  c,  so  as  to  allow 
mercury  to  pass  but  slowly 
from  one  bull)  to  the  other, 
and  thus  control  the  passage 
Fig.  53.  of  gas  through  the  narrow 

delivery  tube  d.      The   other 

end  e  is  provided  with  a  short  piece  of  caoutchouc  tube,  by  blowing 
through  which  any  desired  quantity  of  gas  may  be  readily  delivered. 
Care  must  be  taken  after  use  that  the  delivery  tube  is  not  removed 
from  the  trough  till  the  angle  d  is  filled  with  mercury. 

To  replenish  the  pipette  with  oxygen,  fill  the  bulb  b  and  the 
tubes  c  and  d  with  mercury  ;  introduce  the  point  of  d  into  a  tube 
of  oxygen  standing  in  the  mercury  trough,  and  draw  air  from  the 
tube  e.  The  gas  in  b  is  confined  between  the  mercury  in  c  and 
that  in  d. 

When  the  excess  of  oxygen  has  been  absorbed  as  above  described, 
the  residual  gas,  which  consists  of  nitrogen,  is  measured,  and  the 
analysis  is  complete.* 

There  are  thus  obtained  three  sets  of  observations,  from  which, 
by  the  usual  methods,  we  may  calculate  A  the  total  volume,  B  the 
volume  of  nitric  oxide  and  nitrogen,  and  C  the  volume  of  nitrogen, 
all  reduced  to  0°  C.  and  760  m.m.  pressure ;  from  these  may  be 
obtained — 


*  When  the  quantity  of  carbon  is  very  large  indeed,  traces  of  carbonic  oxide  are 
occasionally  present  in  the  gas,  and  will  remain  with  the  nitrogen  after  treatment  with 
alkaline  pyrogallate.  When  such  excessive  quantities  of  carbon  are  found,  the  stop- 
cock /  should  be  closed  when  the  last  measurement  is  made,  the  laboratory  vessel 
detached,  washed,  and  replaced  filled  with  mercury.  Introduce  then  a  little  solution 
of  cuprous  chloride  (B.  K),  and  return  the  gas  upon  it.  Any  carbonic  oxide  will  be 
absorbed,  and  after  about  five  minutes  the  remaining  nitrogen  may  be  measured.  In 
more  than  twenty  consecutive  analyses  of  waters  of  very  varying  kinds,  not  a  trace  of 
carbonic  oxide  was  found  in  any  of  the  gases  obtained  on  combustion. 


§  83. 


NATURAL  WATERS  AND   SEWAGE. 

A-B  =  vol.  of  CO2, 

B_C  B+C 

— s hO  =  — 0 —  =  vol.  01  JS, 


3" 


and  hence  the  weight  of  carbon  and  nitrogen  can  be  readily  found. 
It  is  much  less  trouble,  however,  to  assume  that  the  gas  in  all 
three  stages  consists  wholly  of  nitrogen  ;  then,  if  A  be  the  weight 
of  the  total  gas,  B  its  weight  after  treatment  with  potassic  hydrate, 
and  C  after  treatment  with  pyrogallate,  the  weight  of  carbon  will 

O  T>     .     /~1 

be  (A  -  B)  -„  and  the  weight  of  nitrogen  —  ~  —  ;  for  the  weights  of 

carbon  and  nitrogen  in  equal  volumes  of  carbonic  anhydride  and 
nitrogen,  at  the  same  temperature  and  pressure,  are  as  6  :  14  ;  and 
the  weights  of  nitrogen  in  equal  volumes  of  nitrogen  and  nitric 
oxide  are  as  2  :  1. 

The  weight  of  1  c.c.  of  nitrogen  at  0°  C.  and  760  m.m.  is  0*0012562 

0-0012562  xv  x 
gin.,  and  the  formula  for  the  calculation  is  w 


in  which  w  =  the  weight  of  nitrogen,  v  the  volume,  p  the  pressure 
corrected  for  tension  of  aqueous  vapour,  and  t  the  temperature  in 
degrees  centigrade.  To  facilitate  this  calculation,  there  is  given  in 

Table  2  the  logarithmic  value  of  the  expression  /^  ' 


for  each  tenth  of  a  degree  from  0°  to  2  9  '9°  C.,  and  in  Table  1  the 
tension  of  aqueous  vapour  in  millimeters  of  mercury.  As  the 
measuring  tube  is  always  kept  moist  with  water,  the  gas  when 
measured  is  always  saturated  with  aqueous  vapour. 

The  following  example  will  show  the  precise  mode  of   calcu- 
lation :  — 


Volume  of  gas         .        .       . 
Temperature   ...» 

Height  of  mercury  in  a,  c,  d 
»  „        b          . 

Difference  . 
Plus  tension  of  aqueous  vapour 


Deduct  correction  for  capillarity . 

Deduct  this  from  height  of  bar 
Tension  of  dry  gas          .        , 

Logarithm  of  volume  of  gas 

0-0012562 

"        (1 +0 -00367t)  760 
„  „        tension  of  dry  gas  . 

Logai-ithm  of  weight  of  gas  calcu 
lated  as  N. 


A                            B 

Total.          After^absor^tion 

4-4888  c.c               0-26227  c.c. 
13-5°                         13-6° 
m.m.                              m.m. 
310-0                        480-0 
193-5                        343-5 

C 
Nitrogen. 

0-26227  c.c. 
13-7° 
m.m. 
480-0 
328-2 

116-5 
11-5 

136-5 
11-6 

151-8 
11-7 

128-0 
0-9 

Add  for  •)„.„ 
capillarity)^ 

2'2 

127'1 

150-3 

165-7 

769-8 
127-1 

769-8 
150-3 

769-8 
165-7 

642-7 

619-5 

604-1 

.      (T65213 

F-41875 

T-41875 

.       6~-19724 
2-80801 

tt-19709 
2-79204 

619694 
2-78111 

i- 
.       3-65738 
=0-0045434 

4-40788 
0-0002558 

4-39680 
0-00024»4gm. 

400  VOLUMETRIC   ANALYSIS.  §    88. 

From  these  weights,  those  of  carbon  and  of  nitrogen  are  obtained 
by  the  use  of  the  formulee  above  mentioned.  Thus — 

A  -  B  =  0-0042876  B  +  C  =  0-0005052 

x 3  -^2 

-^  7)0-0128628  Weight  of  nitrogen,  Q-Q002526 
Weight  of  carbon,  Q-QOlMf" 

When  carbonic  oxide  is  found,  the  corresponding  weight  of 
nitrogen  may  be  found  in  a  similar  manner,  and  should  be  added 
to  that  corresponding  to  the  carbonic  anhydride  before  multiplying 

3 
by  «,  and  must  be  deducted  from  the  weight  corresponding  to  the 

volume  after  absorption  of  carbonic  anhydride. 

As  it  is  impossible  to  attain  to  absolute  perfection  of  manipulation 
and  materials,  each  analyst  should  make  several  blank  experiments 
by  evaporating  a  liter  of  pure  distilled  water  (B.  a)  with  the  usual 
quantities  of  sulphurous  acid  and  chloride  of  iron,  and,  in  addition, 
0*1  gni.  of  freshly  ignited  sodic  chloride  (in  order  to  furnish  a 
tangible  residue).  The  residue  should  be  burnt  and  the  resulting 
gas  analyzed  in  the  usual  way,  and  the  average  amounts  of  carbon 
and  nitrogen  thus  obtained  deducted  from  the  results  of  all 
analyses.  This  correction,  which  may  be  about  O'OOOl  gin.  of  C, 
and  0-00005  gm.  of  N,  includes  the  errors  due  to  the  imperfection 
of  the  vacuum  produced  by  the  Sprengel  pump,  nitrogen  retained 
in  the  cupric  oxide,  ammonia  absorbed  from  the  atmosphere  during 
evaporation,  etc. 

When  the  quantity  of  nitrogen  as  ammonia  exceeds  0'007  part 
per  100,000,  there  is  a  certain  amount  of  loss  of  nitrogen  during 
the  evaporation  by  dissipation  of  ammonia.  This  appears  to  be 
very  constant,  and  is  given  in  Table  3,  which  is  calculated  from 
Table  5,  which  has  been  kindly  furnished  by  Dr.  Frankland. 
The  number  in  this  table  corresponding  to  the  quantity  of  nitrogen 
as  ammonia  present  in  the  water  analyzed  should  be  added  to  the 
amount  of  nitrogen  found  by  combustion.  The  number  thus 
obtained  includes  the  nitrogen  as  ammonia,  and  this  must  be 
deducted  to  ascertain  the  organic  nitrogen.  If  "ammonia"  is 
determined  instead  of  "  nitrogen  as  ammonia,"  Table  5  may  be  used. 

When,  in  operating  upon  sewage,  hydric  metaphosphate  has 
been  employed,  Tables  4  or  6  should  be  used. 

Rules   for   Converting-   Parts   per   100,000  into   Grains  per  Gallon, 
or  the  reverse. 

To  convert  parts  per  100,000  into  grains  per  gallon,  multiply 
by  0-7. 

To  convert  grains  per  gallon  into  parts  per  100,000,  divide 
by  0-7. 

To  convert  grains  per  liter  into  grains  per  gallon,  multiply 
by  70. 


§    88.  NATUKAL  WATERS   AND   SEWAGE.  401 

TABLE   1. 

Elasticity   of  Aqueous    Vapour   for    each   jTjth.  degree   centigrade 
from    GO    to    30°    C.    (Kegrnault) . 


Temp. 
C. 

Tension  in 
Millimeters 
of  Mercury. 

Temp. 
C. 

Tension  in 
Millimeters 
of  Mercury. 

Temp. 
C. 

Tension  in 
Millimeters 
of  Mercury. 

Temp. 
C. 

Tension  in 
Millimeters 
of  Mercury. 

Temp. 
C. 

Tension  in 
Millimeters 
of  Mercury. 

0° 

4-6 

6'0° 

7-0 

12-0° 

10-5 

18-0° 

15*4 

24-0° 

22-2 

•1 

4'6 

•1 

7-0 

•1 

10-5 

•1 

15-5 

•1 

22-3 

•2 

4-7 

•2 

71 

•2 

10-6 

<2 

15-6 

•2 

22-5 

•3 

4-7 

•3 

7-1 

•3 

107 

•3 

157    , 

•3 

22-6 

•1 

4-7 

•4 

7-2 

•4 

107 

•4 

157 

•4 

227 

•5 

4'8 

•5 

7'2 

•5 

10-6 

•5 

15'8 

•5 

22-9 

•6 

4'8 

•6 

7-3 

•6 

10-9 

•6 

15'9 

•6 

23-0 

7 

4'8 

•7 

7'3 

7 

10-9 

7 

16-0 

7 

23-1 

•8 

4'9 

•8 

7'4 

•8 

11-0 

•8 

16-1 

•8 

23-3 

•9 

4-9. 

•9 

7'4 

•9 

11-1 

•9 

16-2 

•9 

23-4 

1-0 

4'9 

7'0 

7'5 

13-0 

11-2 

19-0 

16-3 

25-0 

23-5 

•1 

5-0 

•1 

7'5 

•1 

11-2 

•1 

16-4 

•1 

237 

•2 

5-0 

•2 

7'6 

•2 

]l-3 

•2 

16-6 

•2 

23-8 

•3 

5-0 

•3 

7'6 

•3 

11-4 

•3 

167 

•3 

24-0 

•4 

5-1 

•4 

77 

•4 

11-5 

•4 

16'8 

•4 

24'1 

•5 

5-1 

•5 

7-8 

•5 

11-5 

•5 

16'9 

•5 

24-3 

•6 

5'2 

•6 

7'8 

•6 

11-6 

•6 

17-0 

•6 

24-4 

.  7 

5'2 

•7 

7'9 

•7 

117 

7 

17-1 

7 

24-6 

•8 

5'2 

•8 

7-9 

•8 

11-8 

•8 

17'2 

•8 

247 

•9 

5'3 

•9 

8-0 

•9 

11-8 

•9 

17-3 

•9 

24-8 

2-0 

5'3 

8-0 

8-0 

14-0 

11-9 

20-0 

17-4 

26-0 

25-0 

•1 

5-3 

•1 

81 

•1 

12-0 

•1 

17-5 

•1 

251 

•2 

5'4 

•2 

8-1 

•2 

12-1 

•2 

17-6 

•2 

25'3 

•3 

5'4 

•3 

8'2 

•3 

12-1 

•3 

177 

•3 

25-4 

•4 

5'5 

•4 

8'2 

•4 

12-2 

•4 

17'8 

•4 

25-6 

•5 

5*5 

•5 

8-3 

•5 

12-3 

•5 

17'9 

•5 

257 

•6 

5'5 

•6 

3"3 

•6 

12-4 

•6 

18'0 

•6 

25-9 

7 

5'6 

7 

8'4 

7 

12-5 

7 

18-2 

7 

26-0 

•8 

5'6 

•8 

8'5 

•8 

12-5 

•8 

18-3 

•8 

26-2 

•9 

5-6 

•9 

8-5 

•9 

12-6 

•9 

18-4 

•9 

26-4 

3-0 

57 

9-0 

8'6 

15-0 

127 

21-0 

18-5 

27-0 

26'5 

•1 

57 

•1 

8'6 

•1 

12-8 

•1 

18-6 

•1 

267 

•2 

5-8 

•2 

87 

•2 

12-9 

•2 

187 

•2 

26-8 

•3 

5-8 

•3 

87 

•3 

12-9 

•3 

18-8 

•3 

27'0 

•4 

5-8 

•4 

8'8 

•4 

13-0 

•4 

19-0 

•4 

27'1 

•5 

5-9 

•5 

8'9 

•5 

131 

•5 

19-1 

•5 

27'3 

•6 

5-9 

•6 

8'9 

•6 

13-2 

•6 

19-2 

•6 

27-5 

7 

6-0 

7 

9-0 

7 

13-3 

7 

19-3 

7 

27'6 

•8 

6-0 

•8 

9-0 

•8 

13-4 

•8 

19-4 

•8 

27-8 

•9 

6-1 

'9 

91 

•9 

13-5 

•9 

19-5 

•9 

27-9 

4-0 

6-1 

10-0 

9'2 

16-0 

13-5 

22-0 

197 

28-0 

28-1 

•1 

6-1 

•1 

9'2 

•1 

13-6 

•1 

19'8 

•1 

28-3 

•2 

6-2 

•2 

9-3 

•2 

137 

•2 

19-9 

•2 

28-4 

•3 

6-2 

•3 

9-3 

•3 

13-8 

•3 

20-0 

•3 

28-6 

•4 

6-3 

•4 

9-4 

•4 

13-9 

•4 

20-1 

•4 

28-8 

•5 

6-3 

•5 

9-5 

•5 

14-0 

•5 

20-3 

•5 

28-9 

•6 

6-4 

•6 

9-5 

•6 

14-1 

•6 

20-4 

•6 

291 

•7 

6-4 

7 

9-6 

7 

14-2 

7 

20-5 

7 

29-3 

•8 

6-4 

•8 

97 

•8 

14-2 

•8 

20-6 

•8 

29-4 

•9 

6-5 

•9 

97 

•9 

14-3 

•9 

20-8 

•9 

29-6 

5-0 

6-5 

11-0 

9-8 

17-0 

14-4 

23-0 

20-9 

29-0 

29-8 

•1 

6-6 

1 

9-9 

•1 

14-5 

•1 

21'0 

•1 

30-0 

•2 

6-6 

•2 

9-9 

•2 

14-6 

•2 

211 

•2 

30-1 

•3 

6-7 

•3 

10-0 

•3 

147 

•3 

21-3 

•3 

30-3 

•4 

67 

•4 

10-1 

•4 

14-8 

•4 

21-4 

•4 

30-5 

•5 

6-8 

•5 

10-1 

•5 

14-9 

•5 

21'5 

•5 

307 

•6 

6-8 

•6 

10-2 

•6 

15-0 

•6 

217 

•6 

30-8 

•7 

6-9 

7 

10-3 

7 

15-1 

7 

21-8 

7 

31-0 

•8 

6-9 

•8 

10-3 

•8 

15-2 

•8 

21-9 

•8 

31-2 

•9 

7-0 

'9 

10-4 

•9 

15-3 

•9 

22-1 

•9 

31-4 

D    D 


402 


VOLUMETRIC  ANALYSIS. 


§  88. 


TABLE  2. 

Reduction   of  Cubic   Centimeters   of  Nitrogen  to   Grams. 


Log. 


(1  +  0-003670760 


for  each  tenth  of  a  degree  from  0°  to  30°  C. 


t.c. 

o-o 

01 

0-2 

0-3 

0-4 

0-5 

0-6 

0-7 

0-8 

0-9 

i 

0° 

~6'21824 

808 

793 

777 

761 

745 

729 

713 

697 

681 

1 

665 

649 

633 

617 

601 

586 

570 

554 

538 

522 

2 

507 

491 

475 

459 

443 

427 

412 

396 

380 

364 

3 

349 

333 

318 

302 

286 

270 

255 

239 

223 

208 

4, 

192 

177 

161 

145 

130 

114 

098 

083 

067 

051 

5 

035 

020 

004 

*989 

*973 

*957 

*942 

*926 

*911 

*895 

6 

6-20879 

864 

848 

833 

817 

801 

786 

770 

755 

739 

7 

723 

708 

692 

676 

661 

645 

629 

614 

598 

583 

8 

567 

552 

536 

521 

505 

490 

474 

459 

443 

428 

9 

413 

397 

382 

366 

351 

335 

320 

304 

289 

274 

10 

259 

244 

228 

213 

198 

182 

167 

151 

136 

121 

11 

106 

090 

075 

060 

045 

029 

014 

*999 

*984 

*969 

12 

"6-19953 

938 

923 

907 

892 

877 

862 

846 

831 

816 

13 

800 

785 

770 

755 

740 

724 

709 

694 

679 

664 

14 

648 

633 

618 

603 

588 

573 

558 

543 

528 

513 

15 

497 

482 

467 

452 

437 

422 

407 

392 

377 

362 

16 

346 

331 

316 

301 

286 

271 

256 

241 

226 

211 

17 

196 

181 

166 

151 

136 

121 

106 

091 

076 

061 

18 

046 

031 

016 

001 

*986 

*971 

*956 

*941 

*926 

*911 

19 

6-18897 

882 

867 

852 

837 

822 

807 

792 

777 

762 

20 

748 

733 

718 

703 

688 

673 

659 

644 

629 

614 

21 

600 

585 

570 

555 

540 

526 

511 

496 

481 

466 

22 

452 

437 

422 

408 

393 

378 

363 

349 

334 

319 

23 

305 

290 

275 

261 

246 

231 

216 

202 

187 

172 

24 

158 

143 

128 

114 

099 

084 

070 

055 

041 

026 

25 

012 

*997 

*982 

*968 

*953 

*938 

*924 

*909 

*895 

*880 

26 

"6-17866 

851 

837 

822 

808 

793 

779 

764 

750 

735 

27 

721 

706 

692 

677 

663 

648 

634 

619 

605 

590 

28 

576 

561 

547 

532 

518 

503 

489 

475 

460 

446 

29 

432 

417 

403 

388 

374 

360 

345 

331 

316 

302 

88. 


NATURAL  WATERS   AND   SEWAGE. 


403 


TABLE  3. 

Loss  of  Nitrogen  by  Evaporation  of  NH3. 
With  Sulphurous  Acid. 

Parts  per  100,000. 


Nas 
NH3. 

Loss 

of  N. 

Nas 
NH3. 

Loss 
of  N. 

Nas 
NIP. 

Loss 
of  N. 

Nas 
NH3. 

Loss 
of  N. 

Nas 
NH3. 

Loss 
of  N. 

Nas 
NH3. 

Loss 
of  N. 

5-0 

1741 

3-9 

1-425 

2-8 

•898 

1-7 

•370 

•6 

•145 

•04 

•009 

4-9 

1-717 

3-8 

1-378 

2-7 

•850 

1-6 

•338 

•5 

•109 

•03 

•007 

4-8 

1-693 

37 

1-330 

2-6 

•802 

1-5 

•324 

•4 

•075 

•02 

•005 

47 

1-669 

3-6 

1-282 

2'5 

•754 

T4 

•309 

•3 

•057 

•01 

•003 

4'6 

1-645 

3-5 

1-234 

2-4 

•706 

1-3 

•295 

•2 

•038 

•008 

•002 

4'5 

1-621 

3-4 

1-186 

2-3 

•658 

1-2 

•280 

•1 

•020 

•007 

•001 

4-4 

1-598 

3-3 

1-138 

2-2 

•610 

ri 

•266 

•09 

•018 

4'3 

1-574 

3-2 

1-090 

2-1 

•562 

i-o 

•252 

•08 

•017 

4-2 

1-550 

3-1 

1-042 

2'0 

•514 

•9 

•237 

•07 

•015 

4-1 

1-521 

3-0 

•994 

1-9 

•466 

•8 

•217 

•06 

•013 

4'0 

1-473 

2-9 

•946 

1-8 

•418 

•7 

•181 

•05 

•on 

TABLE  4. 

Loss  of  Nitrogen  by  Evaporation  of  NH3. 
With  Hydric  Metaphosphate. 

Parts  per  100,000. 


a* 

i 

£ 

S-p 

CO* 

Hi 

£ 

0)  o> 

3-p 

eo" 

w 

* 

rf 

re* 

fc* 

r3    0 

« 

"o 

eg 

0 

• 

"o 

1! 

fr 

"o 

£    §* 

rt 

i 

>  §* 

8 

i 

t>  §* 

a 

03 

>•% 

a 

03 

N 

fl 

0) 

* 

fl 

fc 

A 

E 

K 

5 

100  c.c. 

8-2 

•482 

100  c.c. 

5'9 

•385 

100  c.c. 

3'6 

•281 

100  c.c. 

1-3 

•142 

.. 

8-1 

•477 

... 

5-8 

•381 

3'5 

•277 

1-2 

•136 

8-0 

•473 

5'7 

•377 

3'4 

•272 

1-1 

•129 

.. 

7-9 

•469 

... 

5'6 

•373 

3-3 

•267 

'..'. 

1-0 

•123 

7-8 

•465 

5-5 

•368 

3-2 

•261 

•9 

•117 

.. 

77 

•461 

5'4 

•364 

3-1 

•255 

•8 

•111 

.. 

7'6 

•456 

5-3 

•360 

... 

30 

•249 

250c.c. 

•7 

•088 

7-5 

•452 

5-2 

•356 

2-9 

•242 

•6 

•073 

.. 

7-4 

•448 

... 

51 

•352 

2-8 

•236 

•5 

•061 

7-3 

•444 

5-0 

•347 

27 

•230 

SOOc.c. 

•4 

•049 

M 

7-2 

•440 

4-9 

•343 

2-6 

•223 

'3 

•036 

.. 

71 

•435 

4-8 

•338 

2'5 

•217 

lOOOc.c. 

•2 

•024 

7'0 

•431 

4-7 

•334 

2-4 

•211 

•1 

•012 

6'9 

•427 

4'6 

•329 

2-3 

•205 

•09 

•on 

6-8 

•423 

4-5 

•324 

2-2 

•198 

•08 

•010 

.. 

6-7 

•419 

4-4 

•319 

21 

•192 

•07 

•008 

6-6 

•414 

4-3 

•315 

2-0 

•186 

•06 

•007 

6'5 

•410 

... 

4'2 

•310 

1-9 

•180 

•05 

•006 

.. 

6'4 

•406 

4-1 

•305 

1-8 

•173 

•04 

•005 

6'3 

•402 

4-0 

•301 

17 

•167 

•03 

•004 

... 

62 

•398 

3-9 

•296 

1-6 

•161 

•02 

•002 

6-1 

•394 

3-8 

•291 

1-5 

•154 

•01 

•001 

... 

6-0 

•389 

... 

3-7 

•286 

1'4 

•148 

D    D    2 


404  VOLUMETRIC  ANALYSIS. 

TABLE  5. 

Loss  of  Nitrogen  by  Evaporation 
With  Sulphurous  Acid. 

Parts  per  100,000. 


88. 


NH3. 

Loss 
of  N. 

NH3. 

Loss 
of  N. 

NH3. 

Loss 
of  N. 

NH3. 

Loss 
of  N. 

NH3. 

Loss 
of  N. 

NH3. 

Loss 

of  N. 

6-0 

1727 

4-8 

1-451 

3-6 

•977 

2'4 

•503 

1-2 

•250 

•09 

•014 

5'9 

1707 

4.7 

1-411 

3-5 

•937 

2-3 

•463 

1-1 

•238 

•08 

•013 

5-8 

1688 

4-6 

1-372 

3-4 

•898 

2-2 

•424 

i-o 

•226 

•07 

•012 

'  5'7 

1-668 

4-5 

1-332 

3-3 

•858 

2-1 

•384 

•9 

•196 

•06 

•010 

5-6 

1-648 

4-4 

1-293 

32 

•819 

2-0 

•345 

•8 

•166 

•05 

•009 

5-5 

1-628 

4-3 

1-253 

3-1 

•779 

1-9 

•333 

•7 

•136 

•04 

•007 

5-4 

1-609 

4-2 

1-214 

30 

•740 

1-8 

•321 

•6 

•106 

•03 

•006 

5-3 

1-589 

4-1 

1-174 

2-9 

•700 

1-7 

•309 

•5 

•077 

•02 

•004 

52 

1-569 

4-0 

1-135 

2-8 

•661 

1-6 

•297 

•4 

•062 

•01 

•003 

5-1 

1-549 

3-9 

1-095 

2-7 

•621 

1-5 

•285 

•3 

•047 

•009 

•001 

5-0 

1-530 

3-8 

1-056 

2-6 

•582 

1-4 

•274 

•2 

•032 

4-9 

1-490 

37 

1-016 

2-5 

•542 

1-3 

•262 

•1 

•017 

1 

TABLE  6. 

Loss  of  Nitrogen  by  Evaporation 

With  Hydrie  Metaphosphate. 

Parts  per  100,000. 


8* 

ft 

2  ° 

ft 

0)  « 

ft 

<D    Q 

ft 

II 

^. 

CO* 

a  is 

• 

913 

ro* 

W 

"o 

9  £ 

w 

'o 

H 

"o 

IS 

W 

*o 

n 

ft 

1 

l| 

ft 

1 

kl 

ft 

1 

*! 

ft 

1 

100  c.c. 

10-0 

•483 

100  c.c. 

7'2 

•386 

100  c.c. 

4-4 

•283 

100  c.c. 

1-6 

•143 

9-9 

•480 

7-1 

•382 

... 

4-3 

•279 

11 

•137 

9'8 

•476 

7'0 

•379 

4-2 

•275 

1-4 

•132 

... 

97 

•473 

6-9 

•375 

•271 

... 

1*3 

•127 

9'6 

•469 

6'8 

•372 

4-0 

•267 

1*2 

•122 

9'5 

•466 

6-7 

•368 

3'9 

•262 

1-1 

•117 

... 

9-4 

•462 

6-6 

•365 

3'8 

•257 

1-0 

•112 

9-3 

•459 

6'5 

•361 

3'7 

•252 

•250  c.c. 

•9 

•096 

9-2 

•455 

6'4 

•358 

3-6 

•247 

... 

•8 

•080 

9.1 

•152 

6'3 

•354 

3-5 

•242 

•7 

•070 

9-0 

•448 

6'2 

•351 

3-4 

•236 

•6 

•060 

8-9 

•445 

6-1 

•348 

3-3 

•231 

500"c.c. 

•5 

•050 

8-8 

•441 

6-0 

•345 

3-2 

•226 

•4 

•040 

8-7 

•438 

5'9 

•341 

3*1 

•221 

•3 

•030 

... 

8-6 

•434 

5-8 

•337 

3-0 

•216 

1000  c.c. 

•2 

•020 

8-5 

•431 

57 

•333 

29 

•211 

•1 

•010 

8-4 

•428 

5'6 

•330 

28 

•205 

•09 

•009 

8-3 

•424 

c.r 

•326 

27 

•200 

•08 

•008 

8-2 

•421 

5-4 

•322 

26 

•195 

•07 

•007 

8-1 

•417 

5-3 

•318 

2-5 

•190 

•06 

•006 

8-0 

•414 

52 

•314 

2-4 

•184 

•05 

•005 

7-9 

•410 

5-1 

•310 

2'3 

•179 

•04 

•004 

7-8 

•407 

5-0 

•306 

2-2 

•174 

•03 

•003 

7-7 

•403 

4-9 

•302 

... 

2-1 

•169 

•02 

•002 

7-6 

•400 

4-8 

•298 

2-0 

•164 

•01 

•001 

7-5 

•396 

4-7 

•294 

1-9 

•158 

7-4 

•393 

46 

•291 

1-8 

•153 

7-3 

•389 

4-5 

•287 

1-7 

•148 

§    88.  NATURAL  WATEKS  AND    SEWAGE.  405 

5.  Estimation  of  Total  Solid  Matter. — Evaporate  over  a  steam 
or  water  bath  half  a  liter  or  a  less  quantity  of  the  water  in  a  platinum 
dish  which  has  been  heated  to  redness  and  carefully  weighed. 
The  water  should  be  filtered  or  unfiltered,  according  to  the  decision 
made  in  that  respect  at  the  commencement  of  the  analysis.     The 
quantity  to  be  taken  is  regulated  chiefly  by  the  amount  of  nitrate 
present,  as  the  residue  from  this  operation  is,  with  certain  exceptions, 
employed  for  the  determination  of  the  nitrogen  as  nitrates  and 
nitrites.      As  a  general  rule,  for  water  supplies  and  river  water 
half  a  liter  should  be  used;  for  shallow  well  waters,  a  quarter 
of  a  liter.     Of  sewages,  100  c.c.,  and  of  waters  containing  more 
than  0'08  part  of  nitrogen  as  ammonia  per  100,000,  a  quarter  of 
a  liter  will  generally  be  convenient,  as  in  these  cases  the  residue 
will  not  be  used  for  the  estimation  of   nitrogen  as  nitrates  and 
nitrites ;  and  the  only  point  to  be  considered  is  to  have  a  quantity 
of  residue  suitable  to  weigh.    It  is  desirable  to  support  the  platinum 
dish  during  evaporation  in  a  glass  ring  with  a  flange,  shaped  like 
the  top  of  a  beaker,  the  cylindrical  part  being  about  20  m.m.  deep. 
This  is  dropped  into  the  metal  ring  on  the  water  bath,  and  thus 
lines  the  metal  with  glass,  and  keeps  the  dish  clean.     A  glass 
disc  with  a  hole  in  it  to  receive  the  dish  is  not  satisfactory,  as 
drops  of  water  conveying  solid  matter  find  their  way  across  the 
under  surface  from   the  metal  vessel  to  the  dish,  and  thus  soil 
it.     As  soon  as  the  evaporation  is  complete,  the  dish  with  the 
residue  is  removed,  its  outer  side  wiped  dry  with  a  cloth,  and 
it  is  dried  in  a  water  or  steam  oven  for  about  three  hours.     It 
is  then  removed  to  a  desiccator,  allowed  to  cool,  weighed  as  rapidly 
as  possible,  returned  to  the  oven,  and  weighed  at  intervals  of  an 
hour,  until  between  two  successive  weighings  it  has  lost  less  than 
0-001  gm. 

6.  Estimation  of  Nitrogen  as  Nitrates  and  Nitrites. — The  residue 
obtained  in  the  preceding  operation  may  be  used  for  this  estimation. 
Treat  it  with  about  30  c.c.  of  hot  distilled  water,  taking  care  to 
submit  the  whole  of  the  residue  to  its  action.     To  ensure  this  it 
is  advisable  to  rub  the  dish  gently  with  the  finger,  so  as  to  detach 
the  solid  matter  as  far  as  possible,  and  facilitate  the  solution  of 
the  soluble  matters.     The  finger  may  be  covered  by  a  caoutchouc 
finger-stall.     Then  filter  through  a  very  small  filter  of   Swedish 
paper,  washing  the  dish  several  times  with  small  quantities  of  hot 
distilled  water. 

The  filtrate  must  be  evaporated  in  a  very  small  beaker,  over  a 
steam  bath,  until  reduced  to  about  1  c.c.,  or  even  to  dryness. 
This  concentrated  solution  is  introduced  into  the  glass  tube  shown 
in  fig.  54,  standing  in  the  porcelain  mercury  trough,  filled  up  to 
the  stop-cock  with  mercury.  (If  the  nitrometer  of  Lunge  is 
used  in  place  of  Cr urn's  tube,  the  use  of  the  laboratory  tube  and 
gas  apparatus  is  avoided.)  The  tube  is  210  m.m.  in  total  length, 


406  VOLUMETKIC   ANALYSIS.  §    88. 

and  15  m.m.  in  internal  diameter.  By  pouring  the  liquid 
into  the  cup  at  the  top,  and  then  cautiously  opening  the 
stop-cock,  it  may  be  run  into  the  tube  without  admitting 
any  air.  The  beaker  is  rinsed  once  with  a  very  little  hot 
distilled  water,  and  then  two  or  three  times  with  strong 
sulphuric  acid  (c.  a.),  the  volume  of  acid  being  to  that  of 
the  aqueous  solution  about  as  3  :  2.  The  total  volume  of 
acid  and  water  should  be  about  6  c.c.  Should  any  air  by 
chance  be  admitted  at  this  stage,  it  may  readily  be  removed 
by  suction,  the  lips  being  applied  to  the  cup.  With  care 
there  is  but  little  danger  of  getting  acid  into  the  mouth. 

In  a  few  cases  carbonic  anhydride  is  given  off  on 
addition  of  sulphuric  acid,  and  must  be  sucked  out  before 
proceeding. 

Row  grasp  the  tube  firmly  in  the  hand,  closing  the  open 
end  by  the  thumb,  which  should  be  first  moistened; 
withdraw  it  from  the  trough,  incline  it  at  an  angle  of  about 
45°,  the  cup  pointing  from  you,  and  shake  it  briskly  with 
a  rapid  motion  in  the  direction  of  its  length,  so  as  to 
throw  the  mercury  up  towards  the  stop-cock.  After  a 
Pig.  54  very  little  practice  there  is  no  danger  of  the  acid  finding 
its  way  down  to  the  thumb,  the  mixture  of  acid  and 
mercury  being  confined  to  a  comparatively  small  portion  of  the 
tube.  In  a  few  seconds  some  of  the  mercury  becomes  very  finely 
divided;  and  if  nitrates  be  present,  in  about  a  minute  or  less 
nitric  oxide  is  evolved,  exerting  a  strong  pressure  on  the  thumb. 
Mercury  is  allowed  to  escape  as  the  reaction  proceeds,  by  partially, 
but  not  wholly,  relaxing  the  pressure  of  the  thumb.  A  slight 
excess  of  pressure  should  be  maintained  within  the  tube  to  prevent 
entrance  of  air  during  the  agitation,  which  must  be  continued 
until  no  more  gas  is  evolved. 

"When  the  quantity  of  nitrate  is  very  large,  the  mercury,  on 
shaking,  breaks  up  into  irregular  masses,  which  adhere  to  one 
another  as  if  alloyed  with  lead  or  tin,  and  the  whole  forms  a  stiff 
dark-coloured  paste,  which  it  is  sometimes  very  difficult  to  shake ; 
but  nitric  oxide  is  not  evolved  for  a  considerable  time,  then  comes 
off  slowly,  and  afterwards  with  very  great  rapidity.  To  have  room 
for  the  gas  evolved,  the  operator  should  endeavour  to  shake  the 
tube  so  as  to  employ  as  little  as  possible  of  the  contained  mercury 
in  the  reaction.  At  the  close  of  the  operation  the  finely  divided 
mercury  will  consist  for  the  most  part  of  minute  spheres,  the  alloyed 
appearance  being  entirely  gone.  An  experiment  with  a  large 
quantity  of  nitrate  may  often  be  saved  from  loss  by  firmly  resisting 
the  escape  of  mercury,  shaking  until  it  is  judged  by  the  appearance 
of  the  contents  of  the  tube  that  the  reaction  is  complete,  and  then 
on  restoring  the  tube  to  the  mercury  trough,  allowing  the  finely- 
divided  mercury  also  to  escape  in  part.  If  the  gas  evolved  be  not 
more  than  the  tube  will  hold,  and  there  be  no  odour  of  pernitric 


§    88.  NATUKAL  WATERS   AND   SEWAGE.  407 

oxide  from  the  escaped  finely-divided  mercury,  the  operation  may 
be  considered  successful.  If  the  amount  of  nitrate  be  too  large,  a 
smaller  quantity  of  the  water  must  be  evaporated  and  the  operation 
repeated.  When  no  nitrate  is  present,  the  mercury  usually  mani- 
fests very  little  tendency  to  become  divided,  that  which  does  so 
remains  bright,  and  the  acid  liquid  does  not  become  so  turbid  as  it 
does  in  other  cases. 

The  reaction  completed,  the  tube  is  taken  up  closed  by  the 
thumb,  and  the  gas  is  decanted  into  the  laboratory  vessel,  and 
measured  in  the  usual  way  in  the  gas  apparatus.  The  nitric  acid 
tube  is  of  such  a  length,  that  when  the  cup  is  in  contact  with  the 
end  of  the  mercury  trough,  the  open  end  is  just  under  the  centre 
of  the  laboratory  vessel.  If  any  acid  has  been  expelled  from  the 
tube  at  the  close  of  the  shaking  operation,  the  end  of  the  tube  and 
the  thumb  should  be  washed  with  water  before  introducing  into 
the  mercury  trough  of  the  gas  apparatus,  so  as  to  remove  any  acid 
which  may  be  adhering,  which  would  destroy  the  wood  of  the 
trough.  Before  passing  the  gas  into  the  measuring  tube  of  the  gas 
apparatus,  a  little  mercury  should  be  allowed  to  run  over  into  the 
laboratory  vessel  to  remove  the  acid  from  the  entrance  to  the 
capillary  tube. 

As  nitric  oxide  contains  half  its  volume  of  nitrogen,  if  half  a 
liter  of  water  has  been  employed,  the  volume  of  nitric  oxide 
obtained  will  be  equal  to  the  volume  of  nitrogen  present  as  nitrates 
and  nitrites  in  one  liter  of  the  water,  and  the  weight  of  the 
nitrogen  may  be  calculated  as  directed  in  the  paragraph  on  the 
estimation  of  organic  carbon  and  nitrogen. 

When  more  than  0'08  part  of  nitrogen  as  ammonia  is  present  in 
100,000  parts  of  liquid,  there  is  danger  of  loss  of  nitrogen  by 
decomposition  of  ammonic  nitrite  on  evaporation;  and  therefore 
the  residue  from  the  estimation  of  total  solid  matter  cannot  be 
used.  In  such  cases  acidify  a  fresh  quantity  of  the  liquid  with 
dilute  hydric  sulphate,  add  solution  of  potassic  permanganate,  a 
little  at  a  time,  until  the  pink  colour  remains  for  about  a  minute, 
and  render  the  liquid  just  alkaline  to  litmus  paper  with  sodic 
carbonate.  The  nitrites  present  will  then  be  converted  into 
nitrates  and  may  be  evaporated  without  fear  of  loss.  Use  as  little 
of  each  reagent  as  possible.  Sewage  may  be  examined  in  this 
way;  but  it  is  hardly  necessary  to  attempt  the  determination, 
as  sewage  is  almost  invariably  free  from  nitrates  and  nitrites. 
Out  of  several  hundred  specimens,  the  writer  only  found  two 
or  three  which  contained  any,  and  even  then  only  in  very 
small  quantity. 

7.  Estimation  of  Nitrog-en  as  Nitrates  and  Nitrites  in  Waters 
containing1  a  very  large  quantity  of  Soluble  Matter,  with  but  little 
Ammonia  or  Organic  Nitrogen.— When  the  quantity  of  soluble 
matter  is  excessive,  as,  for  example,  in  sea-water,  the  preceding 
method  is  inapplicable,  as  the  solution  to  be  employed  cannot  be 


408  VOLUMETRIC  ANALYSIS.  §    88. 

reduced  to  a  sufficiently  small  bulk  to  go  into  the  shaking  tube. 
If  the  quantity  of  organic  nitrogen  be  less  than  0*1  part  in  100,000, 
the  nitrogen  as  nitrates  and  nitrites  may  generally  be  determined 
by  the  following  modification  of  Schulze's  method  devised  by 
E.  T.  Chapman.  To  200  c.c.  of  the  water  add  10  c.c.  of  sodic 
hydrate  solution  (c.  e),  and  boil  briskly  in  an  open  porcelain  dish 
until  it  is  reduced  to  about  70  c.c.  When  cold  pour  the  residue 
into  a  tall  glass  cylinder  of  about  120  c.c.  capacity,  and  rinse  the 
dish  with  water  free  from  ammonia.  Add  a  piece  of  aluminium 
foil  of  about  15  sq.  centim.  area,  loading  it  with  a  piece  of  clean 
glass  rod  to  keep  it  from  floating.  Close  the  mouth  of  the  cylinder 
with  a  cork,  bearing  a  small  tube  filled  with  pumice  (c.  £),  moistened 
with  hydric  chloride  free  from  ammonia  (c.  17). 

Hydrogen  will  speedily  be  given  off  from  the  surface  of  the 
aluminium,  and  in  five  or  six  hours  the  whole  of  the  nitrogen  as 
nitrates  and  nitrites  will  be  converted  into  ammonia.  Transfer  to 
a  small  retort  the  contents  of  the  cylinder,  together  with  the 
pumice,  washing  the  whole  apparatus  with  a  little  water  free  from 
ammonia.  Distil,  and  estimate  ammonia  in  the  usual  way  with 
Nessler  solution.  It  appears  impossible  wholly  to  exclude 
ammonia  from  the  reagents  and  apparatus,  and  therefore  some 
blank  experiments  should  be  made  to  ascertain  the  correction  to  be 
applied  for  this.  This  correction  is  very  small,  and  appears  to  be 
nearly  constant. 

8.  Estimation  of  Nitrogen  as  Nitrates  and  Nitrites  by  the  Indigo 
Process. — This  method  has  been  fully  described  in  §  67.6. 

9.  Estimation    of    Nitrates    as    Ammonia    by    the    Copper-zinc 
Couple. — It  is  well  known  that  when  zinc  is  immersed  in  copper 
sulphate  solution  it   becomes  covered  with  a  spongy  deposit  of 
precipitated    copper.      If    the    solution    of    copper    sulphate    be 
sufficiently  dilute,  this  deposit  of  copper  is  black  in  colour  and 
firmly  adherent   to  the  zinc.     It   is,   however,   not   so    generally 
known  that  the  zinc  upon  which  copper  has  thus  been  deposited 
possesses  the  power  of   decomposing  pure  distilled  water  at  the 
ordinary  temperature,  and  that  it  is  capable  of   effecting  many 
other  decompositions  which  zinc  alone  cannot.     Among  these  is 
the  decomposition  of  nitrates,  and  the  transformation  of  the  nitric 
acid  into  ammonia.     Gladstone   and   Tribe   have   shown   that 
the  action  of  the  "  copper-zinc  couple  "  (as  they  call  the  conjoined 
metals)  upon  a  nitre  solution  consists  in  the  electrolysis  of  the 
nitre,  resulting  in  the  liberation  of  hydrogen  and  the  formation 
of   zinc  oxide.      This  hydrogen  is  liberated  upon  and  occluded 
by  the  spongy  copper,  and  when  thus  occluded,  it  is  capable  of 
reducing  the  nitre  solution  in  its  vicinity.     The  nitrate  is  first 
reduced   to  nitrite,   and   the  nitrous  acid   is  subsequently  trans- 
formed  into   ammonia   by  the   further   action   of   the  hydrogen. 
M.  W.  Williams  has  shown  (J.  C.  S.  1881,  100)  that  even  in. 


§    88.  NATURAL  WATERS  AND   SEWAGE.  409 

very  dilute  solutions  of  nitre  the  nitric  acid  can  be  completely 
converted  into  ammonia  in  this  manner  with  considerable  rapidity ; 
and  further,  that  the  reaction  may  be  greatly  hastened  by  taking- 
advantage  of  the  influence  of  temperature,  acids,  and  certain 
neutral  salts,  which  increase  the  electrolytic  action  of  the  couple. 
His  experiments  prove  that  carbonic  acid — feeble  acid  as  it  is — 
suffices  to  treble  the  speed  of  the  reaction,  and  that  traces  of  sodic 
chloride  (O'l  per  cent.)  accelerated  it  nearly  as  much  as  carbonic 
acid.  A  rise  of  a  few  degrees  in  temperature  was  also  found  to 
hasten  the  reaction  in  a  very  marked  degree.  The  presence  of 
alkalies,  alkaline  earths,  and  salts  having  an  alkaline  reaction,  was 
found  to  retard  the  speed  of  the  reduction. 

Williams  has,  upon  those  experiments,  founded  a  simple  and 
expeditious  process  for  estimating  the  nitric  and  nitrous  acid  in 
water  analysis,  which,  when  used  with  skill,  may  be  applied  to  by 
far  the  greater  number  of  waters  witli  which  the  analyst  is  usually 
called  upon  to  deal  (Analyst,  1881,  36).  The  requisite  copper-zinc 
couple  is  prepared  in  the  following  manner : — The  zinc  employed 
should  be  clean,  and  for  the  sake  of  convenience  should  be  in  the 
form  of  foil  or  very  thin  sheet.  It  should  be  introduced  into 
a  flask  or  bottle,  and  covered  with  a  solution  of  copper  sulphate, 
containing  about  3  per  cent,  of  the  crystallized  salt,  which  should 
be  allowed  to  remain  upon  it  until  a  copious,  firmly  adherent  coating 
of  black  copper  has  been  deposited.  This  deposition  should  not 
be  pushed  too  far,  or  the  copper  will  be  so  easily  detached  that  the 
couple  cannot  be  washed  without  impairing  its  activity.  When 
sufficient  copper  has  been  deposited  the  solution  should  be  poured 
off,  and  the  conjoined  metals  washed  with  distilled  water.  The 
wet  couple  is  then  ready  for  use. 

To  use  it  for  the  estimation  of  nitrates  it  should  be  made  in 
a  wide-mouthed  stoppered  bottle.  After  washing,  it  is  soaked  with 
distilled  water ;  to  displace  this,  it  is  first  washed  with  some  of  the 
water  to  be  analyzed,  and  the  bottle  filled  up  with  a  further 
quantity  of  the  water.  The  stopper  is  then  inserted,  and  the  bottle 
allowed  to  digest  in  a  warm  place  for  a  few  hours.  If  the  bottle 
be  well  filled  and  stoppered,  the  temperature  may  be  raised  to 
30°  C.,  or  even  higher,  without  any  fear  of  losing  ammonia.  The 
reaction  will  then  proceed  very  rapidly;  but  if  it  be  desired  to 
hasten  the  reaction  still  more,  a  little  salt  should  be  added  (about 
O'l  gm.  to  every  100  c.c.),  or  if  there  be  any  objection  to  this,  the 
water  may  have  carbonic  acid  passed  through  it  for  a  few  minutes 
before  it  is  poured  upon  the  couple.  In  the  case  of  calcareous 
waters,  the  same  hastening  effect  may  be  obtained,  and  the  lime 
may  at  the  same  time  be  removed  by  adding  a  very  little  pure 
oxalic  acid  to  the  water  before  digesting  it  upon  the  couple. 
Williams  has  shown  that  nitrous  acid  always  remained  in  the 
solution  until  the  reaction  was  finished.  By  testing  for  nitrous 
acid  the  completeness  of  the  reaction  may  be  ascertained  with 


410  VOLUMETRIC   ANALYSIS.  §    88. 

certainty,  and  perhaps  the  most  delicate  test  that  can  be  applied 
for  this  purpose  is  that  of  Griess,  in  which  metaphenylene-diamine 
is  the  reagent  employed.  When  a  solution  of  this  substance  is 
added  to  a  portion  of  the  fluid,  and  acidified  with  sulphuric 
acid,  a  yellow  colouration  is  produced  in  about  half  an  hour  if 
the  least  trace  of  a  nitrite  be  present.  The  reaction  easily  detects 
one  part  of  nitrous  acid  in  ten  millions  of  water.  When  no 
nitrous  acid  is  found,  the  water  is  poured  oft  the  couple  into 
a  stoppered  bottle,  and,  if  turbid,  allowed  to  subside.  A  portion 
of  the  clear  fluid,  more  or  less  according  to  the  concentration  of 
the  nitrates  in  the  water,  is  put  into  a  Kessler  glass,  diluted  if 
necessary,  and  titrated  with  Nessler's  reagent  in  the  ordinary 
way. 

This  process  may  be  used  for  the  majority  of  ordinary  waters — 
for  those  that  are  coloured,  and  those  that  contain  magnesium  or 
other  substances  sufficient  to  interfere  with  the  Messier  reagent, 
a  portion  of  the  fluid  poured  oft  the  couple  should  be  put  into 
a  small  retort,  and  distilled  with  a  little  pure  lime  or  sodic  carbonate, 
and  the  titration  of  the  ammonia  performed  upon  the  distillates. 

About  one  square  decimeter  of  zinc  should  be  used  for  every 
200  c.c.  of  a  water  containing  five  parts  or  less  of  nitric  acid  in 
100,000.  A  large  proportion  should  be  used  with  waters  richer 
in  nitrates.  Jhe  couple,  after  washing,  may  be  used  for  two  or 
three  waters  more.  When  either  carbonic  or  oxalic  or  any  other 
acid  has  been  added  to  the  water,  a  larger  proportion  of  Nessler 
reagent  should  be  employed  in  titrating  it  than  it  is  usual  to  add. 
3  c.c.  to  100  of  the  water  are  sufficient  in  almost  all  cases. 

Blunt  (Analyst,  vi.  202)  points  out  that  the  above  process  may 
be  used  without  distillation,  and  with  accuracy,  in  the  case  of  any 
water,  by  adding  oxalic  acid  to  a  double  quantity  of  the  sample, 
dividing,  and  using  one  portion  (clarified  completely  by  subsidence 
in  a  closely  stoppered  bottle)  as  a  comparison  liquid  for  testing 
against  the  other,  which  has  been  treated  with  the  copper-zinc 
couple.  When  dilution  is  used  it  must  be  done  in  both  portions 
equally.  This  plan  possesses  the  advantages  that  an  equal  turbidity 
is  produced  by  Nessler  in  both  portions,  and  any  traces  of 
ammonia  contained  in  the  oxalic  acid  will  have  the  error  due  to  it 
corrected. 

In  calculating  the  amount  of  nitric  acid  contained  in  a  water 
from  the  amount  of  ammonia  obtained  in  this  process,  deductions 
must  of  course  be  made  for  any  ammonia  pre-existing  in  the  water, 
as  well  as  for  that  derived  from  any  nitrous  acid  present. 

10.  Estimation  of  Nitrites  by  Griess' s  Method. — 100  c.c.  of 
the  water  are  placed  in  a  JSTessler  glass,  and  1  c.c.  each  of 
metaphenylene-diamine  and  dilute  acid  (p.  379)  added.  If  colour 
is  rapidly  produced  the  water  must  be  diluted  with  distilled  water 
free  from  N203,  and  other  trials  made.  The  dilution  is  sufficient 


§    88.  NATURAL   WATERS  AND   SEWAGE.  411 

when  colour  is  plainly  seen  at  the  end  of  one  minute.  The  weak 
point  of  the  process  is  that  the  colour  is  progressively  developed  ; 
however,  this  is  of  little  consequence  if  the  comparison  with 
standard  nitrite  is  made  under  the  same  conditions  of  temperature, 
dilution,  and  duration  of  experiment.  Twenty  minutes  is  a 
sufficient  time  for  allowing  the  colours  to  develop  before  final 
comparison. 

M.  W.  Williams  obviates  the  uncertainty  of  the  comparison 
tests  by  using  colourless  Nessler  tubes,  30  in.m.  wide  and 
200  m.m.  long,  graduated  into  millimeters.  They  are  used  as 
follows : — The  comparison  of  the  water  to  be  examined  with  the 
standard  nitrite  is  roughly  ascertained  •  the  glasses  are  then  filled 
to  the  same  height,  and  the  test  added,  and  allowed  to  stand  a  few 
minutes.  Usually  one  will  be  somewhat  deeper  than  the  other. 
The  height  of  the  deeper  coloured  liquid  is  read  off  on  the  scale, 
and  a  portion  removed  with  a  pipette  until  the  colours  correspond. 
The  amount  of  K203  in  the  shortened  column  is  taken  as  equal  to 
the  other,  when  a  simple  calculation  will  show  the  amount  sought. 

11.  Estimation    of    Nitrites    by    Napthylamine. — Waring  to  11 
(/.  C.  S.  1881,  231)  has  drawn  attention  to  this  test,  originally 
devised  by  Griess,  and  which  is  of  such  extreme  delicacy,  that 
by  its  means  it  is  possible  to  detect  one  part  of  N203  in  a  thousand 
millions  of  water. 

Ilosvay  has  improved  this  test  by  using  acetic  acid  instead  of 
a  mineral  acid.  The  colour  is  more  intense  and  more  rapidly 
developed.  He  dissolves  (1)  0*5  gm.  of  sulphanilic  acid  in  150 
c.c.  of  dilute  acetic  acid,  (2)  boils  O'l  gm.  of  a-naphthylamine 
with  20  c.c.  of  water,  pours  off  the  colourless  solution,  and  mixes 
it  with  150  c.c.  of  dilute  acetic  acid.  These  two  solutions  are 
mixed,  thus  gaining  the  advantage  of  having  a  single  reagent 
instead  of  two,  and  one  which  indicates  by  its  colour  whether  it 
has  become  contaminated  by  nitrous  acid  derived  from  the  air.  The 
mixture  is  not  affected  by  light,  but  should  be  protected  from  the 
air.  Should  it,  however,  become  coloured  by  absorption  of  nitrous 
acid,  it  may  be  shaken  with  zinc-dust  and  filtered. 

This  test  is  almost  too  delicate  to  be  used  quantitatively,  but  is 
evidently  very  serviceable  as  a  qualitative  test  for  very  minute 
quantities  of  nitrous  acid.  By  its  means  War  ing  ton  has  detected 
nitrous  acid  in  the  atmosphere  of  various  places  by  exposing  water 
containing  a  few  drops  of  the  requisite  solutions  to  the  air  in  a  basin 
for  a  few  hours ;  the  like  mixture  kept  in  a  closed  flask  or  cylinder 
at  the  same  time  undergoing  no  change  of  colour. 

12.  Estimation  of  Nitrites  by  Potassic  Iodide  and  Starch. — Ekili 
has  pointed  out  (Pliarm.  Trans.  1881,  286)  that  this  well-known 
test  will  give  the  blue  colour  with  nitrous  acid  in  a  few  minutes, 
when  the  proportion  is  one  part  in  ten  millions ;  in  twelve  hours 


412  VOLUMETRIC   ANALYSIS.  §    88. 

when  one  part  in  a  hundred  millions ;  and  in  forty-eight  hours 
when  one  in  a  thousand  millions. 

Ekin  used  acetic  acid  for  acidifying  the  water  to  be  tested,  and 
blank  experiments  with  pure  water  were  simultaneously  carried  on. 
Sulphuric  or  hydrochloric  acid  will,  no  doubt,  give  a  sharper 
reaction,  but  both  these  acids  are  more  liable  to  contain  impurities 
affecting  the  reaction  than  is  the  case  with  pure  acetic  acid.  Owing 
to  the  instability  of  alkaline  iodides,  this  method  of  testing  can 
hardly  be  considered  so  satisfactory  as  the  methods  of  Griess. 

13.  Estimation  of  Suspended  Matter. — Filters  of  Swedish  paper, 
about  110  m.m.  in  diameter,  are  packed  one  inside  another,  about 
15  or  20  together,  so  that  water  will  pass  through  the  whole  group, 
moistened  with  dilute  hydrochloric  acid,  washed  with  hot  distilled 
water  until  the  washings  cease  to  contain  chlorine,  and  dried.  The 
ash  of  the  paper  is  thus  reduced  by  about  60  per  cent.,  and  must 
be  determined  for  each  parcel  of  filter  paper  by  incinerating  10 
niters,  and  weighing  the  ash.  For  use  in  estimating  suspended 
matter,  these  washed  filters  must  be  dried  for  several  hours  at 
120 — 130°  C.,  and  each  one  then  weighed  at  intervals  of  an  hour 
until  the  weight  ceases  to  diminish,  or  at  least  until  the  loss  of 
weight  between  two  consecutive  weighings  does  not  exceed  O'OOOS 
gin.  It  is  most  convenient  to  enclose  the  filter  during  weighing  in 
two  short  tubes  fitting  closely  one  into  the  other.  The  closed  ends 
of  test  tubes,  50  m.m.  long,  cut  off  by  leading  a  crack  round  with 
the  aid  of  a  pastille  or  very  small  gas  jet,  the  sharp  edges  being 
afterwards  fused  at  the  blow-pipe,  answer  perfectly.  Each  pair  of 
tubes  should  have  a  distinctive  number,  which  is  marked  with 
a  diamond  on  both  tubes.  In  the  air  bath  they  should  rest  in 
grooves  formed  by  a  folded  sheet  of  paper,  the  tubes  being  drawn 
apart,  and  the  filter  almost,  but  not  quite,  out  of  the  smaller  tube. 
They  can  then  be  shut  up  whilst  hot  by  gently  pushing  the  tubes 
together,  being  guided  by  the  grooved  paper.  They  require  to 
remain  about  twenty  minutes  in  a  desiccator  to  cool  before  weighing. 
Filtration  will  be  much  accelerated  if  the  filters  be  ribbed  before 
drying.  As  a  general  rule,  it  will  be  sufficient  to  filter  a  quarter 
of  a  liter  of  a  sewage,  half  a  liter  of  a  highly  polluted  river,  and 
a  liter  of  a  less  polluted  water ;  but  this  must  be  frequently  varied 
to  suit  individual  cases.  Filtration  is  hastened,  and  trouble 
diminished,  by  putting  the  liquid  to  be  filtered  into  a  narrow- 
necked  flask,  which  is  inverted  into  the  filter,  being  supported  by 
a  funnel-stand,  the  ring  of  which  has  a  slot  cut  through  it  to  allow 
the  neck  of  the  flask  to  pass.  With  practice  the  inversion  may 
be  accomplished  without  loss,  and  without  previously  closing  the 
mouth  of  the  flask.  When  all  has  passed  through,  the  flask  should 
be  rinsed  out  with  distilled  water,  and  the  rinsings  added  to  the 
filter.  Thus  any  particles  of  solid  matter  left  in  the  flask  are 
secured,  and  the  liquid  adhering  to  the  suspended  matter  and  filter 


§    88.  NATURAL  WATERS  AND   SEWAGE.  413 

is  displaced.  The  filtrate  from  the  washings  should  not  be  added 
to  the  previous  filtrate,  which  may  be  employed  for  determination 
of  total  solid  matter,  chlorine,  hardness,  etc. 

Thus  washed,  the  filter  with  the  matter  upon  it  is  dried  at 
100°  C.,  then  transferred  from  the  funnel  to  the  same  pair  of  tubes 
in  which  it  was  previously  weighed,  and  the  operation  of  drying  at 
120°  —  130°  C.  and  weighed  until  constant  repeated.  The  weight 
thus  obtained,  minus  the  weight  of  the  empty  filter  and  tubes, 
gives  the  weight  of  the  total  suspended  matter  dried  at  120°  -  130°  C. 

To  ascertain  the  quantity  of  mineral  matter  in  this,  the  filter 
with  its  contents  is  incinerated  in  a  platinum  crucible,  and  the 
total  ash  thus  determined,  minus  the  ash  of  the  filter  alone,  gives 
the  weight  of  the  mineral  suspended  matter. 

14.  Estimation  of  Chlorine  present  as  Chloride. — To   50   C.C.    of 
the  water  add  two  or  three  drops  of  solution  of  potassic  chromate 
(D.  /3),  so  as  to  give  it  a  faint  tinge  of  yellow,  and  add  gradually 
from  a  burette  standard  solution  of  silver  nitrate  (D.  a),  until  the 
red   silver   chromate   which    forms    after    each   addition   of    the 
nitrate  ceases  to  disappear  on  shaking.     The  number  of  c.c.   of 
silver   solution    employed   will    express   the   chlorine   present   as 
chloride  in  parts  in  100,000.     If  this  amount  be  much  more  than 
10,  it  is  advisable  to  take  a  smaller  quantity  of  water. 

If  extreme  accuracy  be  necessary,  after  completing  a  determination, 
destroy  the  slight  red  tint  by  an  excess  of  a  soluble  chloride,  and 
repeat  the  estimation  on  a  fresh  quantity  of  the  water  in  a  similar 
flask  placed  by  the  side  of  the  former.  By  comparing  the  contents 
of  the  flasks,  the  first  tinge  of  red  in  the  second  flask  may  be 
detected  with  great  accuracy.  It  is  absolutely  necessary  that  the 
liquor  examined  should  not  be  acid,  unless  with  carbonic  acid,  nor 
more  than  very  slightly  alkaline.  It  must  also  be  colourless,  or 
nearly  so.  These  conditions  are  generally  found  in  waters,  but,  if 
not,  they  may  be  brought  about  in  most  cases  by  rendering  the 
liquid  just  alkaline  with  lime  water  (free  from  chlorine),  passing 
carbonic  anhydride  to  saturation,  boiling,  and  filtering.  The  calcic 
carbonate  has  a  powerful  clarifying  action,  and  the  excess  of  alkali 
is  exactly  neutralized  by  the  carbonic  anhydride.  If  this  is  not 
successful,  the  water  must  be  rendered  alkaline,  evaporated  to 
dryness,  and  the  residue  gently  heated  to  destroy  organic  matter. 
The  chlorine  may  then  be  extracted  with  water,  and  estimated  in 
the  ordinary  way,  either  gravimetrically  or  volumetrically. 

15.  Estimation  of  Hardness. — The  following  method,  devised  by 
the  late  Dr.  Thomas  Clark,  of  Aberdeen,  is  in  general  use;  and 
from  its  ease,  rapidity,   and   accuracy,   is  of   great   value.     (For 
estimating    the    hardness   of    waters   without   soap   solution   see 
page  66.) 

Uniformity  in  conducting  it  is  of  great  importance ;  especially 


414 


VOLUMETRIC  ANALYSIS. 


the  titration  of  the  soap  solution,  and  the  estimation  of  the  hardness 
of  waters,  should  be  performed  in  precisely  similar  ways. 

Measure  50  c.c.  of  the  water  into  a  well-stoppered  bottle  of  about 
250  c.c.  capacity,  shake  briskly  for  a  few  seconds,  and  suck  the 
air  from  the  bottle  by  means  of  a  glass  tube,  in  order  to  remove 
any  carbonic  anhydride  which  may  have  been  liberated  from  the 
water.  Add  standard  soap  solution  (E.  /3)  from  a  burette,  one  c.c. 
at  a  time  at  first,  and  smaller  quantities  towards  the  end  of  the 
operation,  shaking  well  after  each  addition,  until  a  soft  lather  is 
obtained,  which,  if  the  bottle  is  placed  at  rest  on  its  side,  remains 
continuous  over  the  whole  surface  for  five  minutes.  The  soap 
should  not  be  added  in  larger  quantities  at  a  time,  even  when  the 
volume  required  is  approximately  known.  This  is  very  important. 

When  more  than  16  c.c.  of  soap  solution  are  required  by  50  c.c. 
of  the  water,  a  less  quantity  (as  25  or  10  c.c.)  of  the  latter  should 
be  taken,  and  made  up  to  50  c.c.  with  recently  boiled  distilled 
water,  so  that  less  than  16  c.c.  of  soap  solution  will  suffice,  and  the 
number  expressing  the  hardness  of  the  diluted  water  multiplied  by 
2  or  5,  as  the  case  may  be. 

When  the  water  contains  much  magnesium,  which  may  be 
known  by  the  lather  having  a  peculiar  curdy  appearance,  it  should 
be  diluted,  if  necessary,  with  distilled  water,  until  less  than  7  c.c. 
are  required  by  50  c.c. 

The  volume  of  standard  soap  solution  required  for  50  c.c.  of  the 
water  being  known,  the  weight  of  calcic  carbonate  (CaCO3)  corres- 
ponding to  this  may  be  ascertained  from  the  following  Table  7*  :— 

*  The  table  is  calculated  from  that  originally  constructed  "by  Dr.  Clark,  which  is 
as  follows :  — 

Differences  for  the 
next  1°  of  hardness. 
1-8 
2'2 
2'2 
2-0 
2'0 
2-0 
2-0 
1-9 
1-9 
1-9 
1-8 
1-8 
1-8 
1-8 
1-8 
17 

Each  "measure"  being  10  grains,  the  volume  of  water  employed  1000  grains,  and  each 
"  degree  "  1  grain  of  calcic  carbonate  in  a  gallon. 

If  the  old  weights  and  measures,  grains  and  gallons,  be  preferred,  this  table  may  be 
used,  the  process  being  exactly  as  above  described,  but  1000  grains  of  water  taken 
instead  of  50  c.c.,  and  the  soap  solution  measured  in  10-grain  measures  instead  of  cubic 
centimeters.  If  the  volume  of  soap  solution  used  be  found  exactly  in  the  second  column 
of  the  table,  the  hardness  will,  of  course,  be  that  shown  on  the  same  line  in  the  first 
column.  But  if  it  be  not,  deduct  from  it  the  next  lower  number  in  the  second  column, 
when  the  corresponding  degree  of  hardness  in  the  first  column  will  give  the  integral 
part  of  the  result ;  divide  the  remainder  by  the  difference  on  the  same  line  in  the  third 
column,  and  the  quotient  will  give  the  fractional  part.  For  example,  if  1000  grains  of 
water  require  16  "  measures  "  of  soap,  the  calculation  will  be  as  follows :— 


Degree  of  Hardness. 
0°  (Distilled  water) 

Measures  of 
Soap  Solution. 
1-4 

1 

3-2 

2 

5'4 

3 

7-6 

4 

9-6 

5 

11-6 

6 

13-6 

7 

15-6 

8 

17-5 

9 

19-4 

10 

21-3 

11 

23-1 

12 

24-9 

13 

267 

14 

28-5 

15 

30'3 

16 

32-0 

88. 


NATURAL   WATERS   AND   SEWAGE. 


415 


TABLE    7. 

Table  of  Hardness,  Parts  in  100,000. 


Volume  of 
Soap 
Solution. 

Oo~ 

<5S 
» 

Volume  of 
Soap 
Solution. 

O  cT 
O  t~t 

fr 

Volume  of 
Soap 
Solution. 

sJ 

» 

Volume  of 
Soap 
Solution. 

„§•  ! 

O  ^ 
O  o" 

c3  O 

fe 

c.c. 

c.c. 

c.c. 

c.c. 

4'0 

4-57 

8-0 

10-30 

12-0 

16-43 

1 

•71 

1 

•45 

1 

•59 

2 

•86 

2 

•60 

2 

•75 

3 

5-00 

3 

•75 

3 

•90 

4 

•14 

4 

•90 

4 

17'06 

5 

•29 

5 

11-05 

5 

•22 

6 

•43 

6 

•20 

6 

•38 

07 

•oo 

7 

•57 

7 

•35 

7 

•54, 

0-8 

•16 

8 

•71 

8 

•50 

8 

•70 

0-9 

•32 

9 

•86 

9 

•65 

9 

•86 

I'O 

•48 

5'0 

6-00 

9*0 

•80 

13-0 

18-02 

1 

•63 

1 

•14 

1 

•95 

1 

•17 

2 

•79 

2 

•29 

2 

12-11 

2 

•33 

3 

•95 

3 

•43 

3 

•26 

3 

•49 

4 

I'll 

4 

•57 

4 

•41 

4 

•65 

5 

•27 

5 

•71 

5 

•56 

5 

•81 

6 

•43 

6 

•86 

6 

•71 

6 

•97 

7 

•56 

7 

7-00 

7 

•86 

7 

19-13 

8 

•69 

8 

•14 

8 

13-01 

8 

•29 

9 

•82 

9 

•29 

9 

•16 

9 

•44 

2'0 

•95 

6-0 

•43 

10-0 

•31 

14-0 

•60 

1 

2-08 

1 

•57 

1 

•46 

1 

•76 

2 

•21 

2 

•71 

2 

•61 

2 

•92 

3 

•34 

3 

•86 

3 

•76 

3 

20-08 

4 

•47 

4 

8-00 

4 

•91 

4 

•24 

5 

•60 

5 

•14 

5 

14-06 

5 

•40 

6 

•73 

6 

•29 

6 

•21 

6 

•56 

7 

•86 

7 

•43 

7 

•37 

7 

•71 

8 

•99 

8 

•57 

8 

•52 

8 

•87 

9 

3-12 

9 

•71 

9 

•68 

9 

21-03 

3-0 

•25 

7-0 

•86 

ll'O 

•84 

15-0 

•19 

1 

•38 

1 

9-00 

1 

15-00 

1 

•35 

2 

•51 

2 

•14 

2 

•16 

2 

•51 

3 

•64 

3 

•29 

3 

•32 

3 

•68 

4 

•77 

4 

•43 

4 

•48 

4 

•85 

5 

•90 

5 

•57 

5 

•63 

5 

22'02 

6 

4-03 

6 

•71 

6 

•79 

6 

•18 

7 

•16 

7 

•8i 

7 

•95 

7 

•35 

8 

•29 

8 

10-00 

8 

16-11 

8 

•52 

3-9 

•43 

7'9 

•15 

11-9 

•27 

9 

•69 

16-0 

•8fi 

16-0 
—15-6  (-7°  hardness). 


(Difference=) 


•21 


therefore  the  hardness  is  7'21  grains  of  CaCO3  per  gallon.  The  water  must  be  diluted 
with  distilled  water  if  necessary,  so  that  the  quantity  of  soap  required  does  not  exceed 
32  measures  in  ordinary  waters,  and  14  measures  in  water  containing  much  magnesia. 


416  VOLUMETRIC   ANALYSIS.  §    88. 

When  water  containing  calcic  and  magnesic  carbonates,  held 
in  solution  by  carbonic  acid,  is  boiled,  carbonic  anhydride  is 
expelled,  and  the  carbonates  precipitated.  The  hardness  due  to 
these  is  said  to  be  temporary,  whilst  that  due  to  sulphates, 
chlorides,  etc.,  and  to  the  amount  of  carbonates  soluble  in  pure 
water  (the  last-named  being  about  three  parts  per  100,000)  is 
called  permanent. 

To  estimate  permanent  hardness,  a  known  quantity  of  the  water 
is  boiled  gently  for  half  an  hour  in  a  flask,  the  mouth  of  which 
is  freely  open.  At  the  end  of  the  boiling,  the  water  should  be 
allowed  to  cool,  and  the  original  weight  made  up  by  adding 
recently  boiled  distilled  water. 

Much  trouble  may  be  avoided  by  using  flasks  of  about  the  same 
w  eight,  and  taking  so  much  water  in  each  as  will  make  up  the 
same  uniform  weight.  Thus  if  all  the  flasks  employed  weigh 
less  than  50  gm.  each,  let  each  flask  with  its  contents  be  made  to 
weigh  200  gm. 

After  boiling  and  making  up  to  the  original  weight,  filter  the 
water,  and  determine  the  hardness  in  the  usual  way.  The  hardness 
thus  found,  deducted  from  that  of  the  unboiled  water,  will  give 
the  temporary  hardness. 

16.  Mineral  Constituents  and  Metals. — The  quantities  of  the 
following  substances  which  may  be  present  in  a  sample  of  water 
are  subject  to  such  great  variations,  that  no  definite  directions  can 
be  given  as  to  the  volume  of  water  to  be  used.  The  analyst  must 
judge  in  each  case  from  a  preliminary  experiment  what  will  be 
a  convenient  quantity  to  take. 

Sulphuric  Acid. — Acidify  a  liter  or  less  of  the  water  with 
hydrochloric  acid,  concentrated  on  the  water  bath  to  about  100  c.c., 
and  while  still  hot  add  a  slight  excess  of  baric  chloride.  Filter, 
wash,  ignite,  and  weigh  as  baric  sulphate,  or  estimate  volumetrically, 
as  in  §  73. 

Sulphuretted  Hydrogen. — Titrate  with  a  standard  solution  of 
iodine,  as  in  §  74.3. 

Phosphoric  Acid. — This  substance  may  be  determined  in  the 
solid  residue  obtained  by  evaporation,  by  moistening  it  with  nitric 
acid,  and  again  drying  to  render  silica  insoluble ;  the  residue  is 
again  treated  with  dilute  nitric  acid,  filtered,  molybdic  solution 
(p.  272)  added,  and  set  aside  for  twelve  hours  in  a  warm  place ; 
filter,  dissolve  the  precipitate  in  ammonia,  precipitate  with  magnesia 
mixture,  and  weigh  as  magnesic  pyrophosphate,  or  estimate  volu- 
metrically as  in  §  69.5. 

Another  method  is  to  add  to  500  c.c.  of  the  sample  about  10  c.c. 
of  solution  of  alum,  then  a  few  drops  of  ammonia,  lastly  acidify 
slightly  with  acetic  acid,  and  set  aside  to  allow  the  precipitated 
A1PW  to  settle.  The  clear  liquid  may  then  be  poured  off*,  the  pre- 
cipitate dissolved  in  nitric  acid  and  estimated  with  molybdic  solution. 


§    88.  NATUEAL   WATERS   AND   SEWAGE.  417 

Silicic  Acid. — Acidify  a  liter  or  more  of  the  water  with 
hydrochloric  acid,  evaporate,  and  dry  the  residue  thoroughly. 
Then  moisten  with  hydrochloric  acid,  dilute  with  hot  water,  and 
iilter  off,  wash,  ignite,  and  weigh  the  separated  silica. 

Iron. — To  the  nitrate  from  the  estimation  of  silicic  acid  add  a  few 
drops  of  nitric  acid,  dilute  to  about  100  c.c.,  and  estimate  by  colour 
titration,  as  in  §  60.4 ;  or  where  the  amount  is  large,  add  excess  of 
ammonia,  and  heat  gently  for  a  short  time.  Filter  off  the  precipitate, 
and  estimate  the  iron  in  the  washed  precipitate  volumetrically,  as 
in  §  59  or  60. 

Calcium. — To  the  nitrate  from  the  iron  estimation  add  excess  of 
ammonic  oxalate,  filter  off  the  calcic  oxalate,  ignite  and  weigh  as 
calcic  carbonate,  or  estimate  volumetrically  with  permanganate, 
as  in  §  48. 

Magnesium. — To  the  concentrated  filtrate  from  the  calcium 
estimation  add  sodic  phosphate  (or,  if  alkalies  are  to  be  determined 
in  the  filtrate,  ammonic  phosphate),  and  allow  to  stand  for  twelve 
hours  in  a  warm  place.  Filter,  ignite  the  precipitate,  and  weigh  as 
magnesic  pyrophosphate,  or,  before  ignition,  titrate  with  uranium. 

Barium. — Is  best  detected  in  a  water  by  acidifying  with 
hydrochloric  acid,  filtering  perfectly  clear  if  necessary,  then 
add  a  clear  solution  of  calcic  sulphate,  and  set  aside  in  a  warm 
place.  Any  white  precipitate  which  forms  is  due  to  barium. 

Potassium  and  Sodium. — These  are  generally  determined  jointly, 
and  for  this  purpose  the  filtrate  from  the  magnesium  estimation 
may  be  used.  Evaporate  to  dryness,  and  heat  gently  to  expel 
ammonium  salts,  remove  phosphoric  acid  with  plumbic  acetate,  and 
the  excess  of  lead  in  the  hot  solution  by  ammonia  and  ammonic 
carbonate.  Filter,  evaporate  to  dryness,  heat  to  expel  ammonium 
salts,  and  weigh  the  alkalies  as  chlorides. 

It  is,  however,  generally  less  trouble  to  employ  a  separate 
portion  of  water.  Add  to  a  liter  or  less  of  the  water  enough  pure 
baric  chloride  to  precipitate  the  sulphuric  acid,  boil  with  pure  milk 
of  lime,  filter,  concentrate,  and  remove  the  excess  of  lime  with 
ammonic  carbonate  and  a  little  oxalate.  Filter,  evaporate,  and 
weigh  the  alkaline  chlorides  in  the  filtrate.  If  the  water  contains 
but  little  sulphate,  the  baric  chloride  may  be  omitted,  and  a  little 
ammonic  chloride  added  to  the  solution  of  alkaline  chlorides. 

If  potassium  and  sodium  must  each  be  estimated,  separate  them 
by  means  of  platinic  chloride ;  or,  after  weighing  the  mixed 
chlorides,  determine  the  chlorine  present  in  them,  and  calculate  the 
amounts  of  potassium  and  sodium  by  the  following  formula : — 
Calculate  all  the  chlorine  present  as  potassic  chloride ;  deduct  this 
from  the  weight  of  the  mixed  chlorides,  and  call  the  difference  d. 
Then  as  16'1  :  58'37  :  :  d  :  KaCl  present.  (See  also  §  38.) 

E    E 


418  VOLUMETRIC   ANALYSIS.  §    88. 

Lead. — May  be  estimated  by  the  method  proposed  by  Miller. 
Acidulate  the  water  with  two  or  three  drops  of  acetic  acid,  and 
add  -^j-  of  its  bulk  of  saturated  aqueous  solution  of  sulphuretted 
hydrogen.  Compare  the  colour  thus  produced  in  the  colorimeter 
or  a  convenient  cylinder,  with  that  obtained  with  a  known  quantity 
of  a  standard  solution  of  a  lead  salt,  in  a  manner  similar  to  that 
described  for  the  estimation  of  iron  (§  60.4).  The  lead  solution 
should  contain  0*1831  gm.  of  normal  crystallized  plumbic  acetate  in 
a  liter  of  distilled  water,  and  therefore  each  c.c.  contains  O'OOOl  gm. 
of  metallic  lead. 

It  is  obvious  that  in  the  presence  of  copper  or  other  heavy  metals 
the  colour  produced  by  the  above  method  will  all  be  ascribed  to 
lead;  it  is  preferable,  therefore,  to  adopt  the  method  of  Harvey 
(Analyst,  vi.  146),  in  which  the  lead  is  precipitated  as  chromate. 
The  results,  however,  are  not  absolute  as  to  quantity,  except  so 
far  as  the  eye  may  be  able  to  measure  the  amount  of  precipitate. 

The  standard  lead  solution  is  the  same  as  in  the  previous 
method.  The  precipitating  agent  is  pure  potassic  bichromate,  in 
fine  crystals  or  powder. 

250  c.c.  or  so  of  the  water  is  placed  in  a  Phillips' jar  with 
a  drop  or  two  of  acetic  acid,  and  a  few  grains  of  the  reagent  added, 
and  agitated  by  shaking.  One  part  of  lead  in  a  million  parts  of 
water  will  show  a  distinct  turbidity  in  five  minutes  or  less.  In  six 
or  eight  hours  the  precipitate  will  have  completely  settled,  and  the 
yellow  clear  liquid  may  be  poured  off  without  disturbing  the 
sediment,  which  may  then  be  shaken  up  with  a  little  distilled 
water,  and  its  quantity  judged  by  comparison  with  a  similar 
experiment  made  with  the  standard  lead  solution. 

Copper. — Estimate  by  colour  titration,  as  in  §  54.9. 

Arsenic. — Add  to  half  a  liter  or  more  of  the  water  enough  . 
sodic  hydrate,  free  from  arsenic,  to  render  it  slightly  alkaline, 
evaporate  to  dryness,  and  extract  with  a  little  concentrated 
hydrochloric  acid.  Introduce  this  solution  into  the  generating  flask 
of  a  small  Marsh's  apparatus,  and  pass  the  evolved  hydrogen,  first 
through  a  U-tube  filled  with  pumice,  moistened  with  plumbic 
acetate,  and  then  through  a  piece  of  hard  glass  tube  about  150  m.m. 
in  length,  and  3  m.m.  in  diameter  (made  by  drawing  out  combustion 
tube).  At  about  its  middle,  this  tube  is  heated  to  redness  for  a 
length  of  about  20  m.m.  by  the  flame  of  a  small  Bunsen  burner, 
and  here  the  arsenetted  hydrogen  is  decomposed,  arsenic  being 
deposited  as  a  mirror  on  the  cold  part  of  the  tube.  The  mirror 
obtained  after  the  gas  has  passed  slowly  for  an  hour  is  compared 
with  a  series  of  standard  mirrors  obtained  in  a  similar  way  from 
known  quantities  of  arsenic.  Care  must  be  taken  to  ascertain  in 
each  experiment  that  the  hydrochloric  acid,  zinc,  and  whole  apparatus 
are  free  from  arsenic,  by  passing  the  hydrogen  slowly  through  the 
heated  tube  before  introducing  the  solution  to  be  tested. 


§    89.  NATURAL  WATERS  AND   SEWAGE.  419 

Zinc. — This  metal  exists  in  waters  as  bicarbonate,  and  on 
exposure  of  such  waters  in  open  vessels  a  film  of  zinc  carbonate 
forms  on  the  surface ;  this  is  collected  on  a  platinum  knife  or  foil 
and  ignited.  The  residue  is  of  a  yellow  colour  when  hot,  and 
turns  white  on  cooling.  The  reaction  is  exceedingly  delicate. 


THE    INTERPRETATION    OF    THE    RESULTS   OF    ANALYSIS. 

§  89.  THE  primary  form  of  natural  water  is  rain,  the  chief  impurities  in 
which  are  traces  of  organic  matter,  ammonia,  and  ammonic  nitrate  derived 
from  the  atmosphere.  On  reaching  the  ground  it  becomes  more  or  less 
charged  with  the  soluble  constituents  of  the  soil,  such  as  calcic  and  magnesic 
carbonates,  potassic  and  sodic  chlorides,  and  other  salts,  which  are  dissolved, 
some  by  a  simple  solvent  action,  others  by  the  agency  of  carbonic  acid  in 
solution.  Draining  off  from  the  land,  it  will  speedily  find  its  way  to  a  stream 
which,  in  the  earlier  part  of  its  course,  will  probably  be  free  from  pollution  by 
animal  matter,  except  that  derived  from  any  manure  which  may  have  been 
applied  to  the  land  on  which  the  rain  fell.  Thus  comparatively  pure,  it  will 
furnish  to  the  inhabitants  on  its  banks  a  supply  of  water  which,  after  use, 
will  be  returned  to  the  stream  in  the  form  of  sewage  charged  with  impurity 
derived  from  animal  excreta,  soap,  household  refuse,  etc.,  the  pollution  being 
perhaps  lessened  by  submitting  the  sewage  to  some  purifying  process,  such  as 
irrigation  of  land,  filtration,  or  clarification.  The  stream  in  its  subsequent 
course  to  the  sea  will  be  in  some  measure  purified  by  slow  oxidation  of  the 
organic  matter,  and  by  the  absorbent  action  of  vegetation,  but  not  to 
any  great  extent.  Some  of  the  rain  will  not,  however,  go  directly  to  a 
stream,  but  sink  through  the  soil  to  a  well.  If  this  be  shallow,  it  may 
be  considered  as  merely  a  pit  for  the  accumulation  of  drainage  from  the 
immediately  surrounding  soil,  which,  as  the  well  is  in  most  cases  close  to 
a  dwelling,  will  be  almost  inevitably  charged  with  excretal  and  other  refuse ; 
so  that  the  water  when  it  reaches  the  well  will  be  contaminated  with  soluble 
impurities  thence  derived,  and  with  nitrites  and  nitrates  resulting  from  their 
oxidation.  After  use  the  water  from  the  well  will,  like  the  river  water,  form 
sewage,  and  find  its  way  to  a  river,  or  again  to  the  soil,  according  to 
circumstances. 

In  the  case  of  a  deep  well,  from  which  the  surface  water  is  excluded,  the 
conditions  are  different.  The  shaft  will  usually  pass  through  an  impervious 
stratum,  so  that  the  water  entering  it  will  not  be  derived  from  the  rain  which 
falls  on  the  area  immediately  surrounding  its  mouth,  but  from  that  which  falls 
on  the  outcrop  of  the  pervious  stratum  below  the  impervious  one  just 
mentioned;  and  if  this  outcrop  be  in  a  district  which  is  uninhabited  and 
uncultivated,  the  water  of  the  well  will  probably  be  entirely  free  from  organic 
impurity  or  products  of  decomposition.  But  even  if  the  water  be  polluted 
at  its  source,  still  it  must  pass  through  a  very  extensive  filter  before  it  reaches 
the  well,  and  its  organic  matter  will  probably  be  in  great  measure  converted 
by  oxidation  into  bodies  in  themselves  innocuous. 

This  is  very  briefly  the  general  history  of  natural  waters,  and  the  problem 
presented  to  the  analyst  is  to  ascertain,  as  far  as  possible,  from  the  nature  and 
quantity  of  the  impurities  present,  the  previous  history  of  the  water,  and  its 
present  condition  and  fitness  for  the  purpose  for  which  it  is  to  be  used. 

It  is  impossible  to  give  any  fixed  rule  by  which  the  results  obtained  by  the 
foregoing  method  of  analysis  should  be  interpreted.  The  analyst  must  form 
an  independent  opinion  for  each  sample  from  a  consideration  of  all  the  results 
he  has  obtained.  Nevertheless,  the  following  remarks,  illustrated  by  reference 
to  the  examples  given  in  the  accompanying  table,  which  may  be  considered 
as  fairly  typical,  will  probably  be  of  service.  (See  pages  420  and  421.) 

E   E  2 


420 

TABLE    8. 


VOLUMETRIC  ANALYSIS.  §    89. 

Results  of  Analysis  expressed 


Number 
of 
Sample. 

DESCRIPTION. 

REMARKS. 

Upland   Surface  Waters. 

I. 

The  Dee  above  Balmoral,  March  9th,  1872 

Clear      

II. 

Glasgow  Water  supply  from  Loch  Katrine  —  average  of  ") 
monthly  analyses  during  five  years,  1876  —  81            j 

Clear;  very  pale  brov 

III. 
IV. 

Liverpool  Water  supply  from  Eivington  Pike,  June  4th,1869 
Manchester  Water  supply,  May  9th,  1874 

Clear      
Turbid  

V. 

Cardiff  Water  supply,  Oct.  18th,  1872 

Clear      

Surface  Water  from   Cultivated   Land. 

VI. 

Dundee  Water  supply,  March  12th,  1872 

Turbid  ;  brownish  yelk 

VII. 

Norwich  Water  supply,  June  18th,  1872 

Slightly  turbid... 

Shallow  Wells. 

VIII. 

Cirencester,  Market  Place,  Nov.  4th,  1870 

Slightly  turbid... 

IX. 

Marlborough,  College  Yard,  Aug.  22nd,  1873  ... 

Clear      

X. 

Birmingham,  Hurst  Street,  Sept.  18th,  1873    ... 

Clear;  strong  saline  tas 

C  Very  turbid  &  offen- 

XI. 

Sheffield,  Well  near,  Sept.  27th,  1870 

\      sive.      Swarming 

(.     with  bacteria,  &c. 

XII. 
XIII. 

London,  Aldgate  Pump,  June  5th,  1872 
London,  Wellclose  Square,  June  5th,  1872 

Clear      
Slightly  turbid;  salineta 

XIV. 

Leigh,  Essex,  Churchyard  Well,  Nov.  28th,  1871 

Slightly  turbid... 

Deep  Wells. 

XV. 

Birmingham,  Short  Heath  Well,  May  16th,  1873 

Clear    

XVI. 

Caterham,  Water  Works  Well,  Feb.  14th,  1873 

Clear     

Ditto,  Softened  (Water  supply) 

XVII. 

London,  Albert  Hall,  May,  1872 

Slightly  turbid... 

XVIII. 

Gravesend,  Railway  Station,  Jan.  17th,  1873    ... 

Clear     

Springs. 

XIX. 

Dartmouth  Water  supply,  Jan.  8th,  1873 

Turbid  

XX. 

Grantham  Water  supply,  July  llth,  1873 

Clear     

London  Water  supply—  average  monthly  analyses  dur 

ing  21  years,  1869—8 

XXI. 

From  the  Thames 

XXII. 

From  the  Lea 

... 

XXIII. 

From  Deep  Chalk  Wells  (Kent  Company) 

XXIV. 
XXV. 

Ditto  (Colne  Valley  Co.)  softened—  thirteen  years,  1877—89 
Ditto  (Tottenham)—  thirteen  years,  1877—89  ... 

XXVI. 

Birmingham   Water    supply—  average    monthly   analy 

ses,  1875-1880. 

Average   Composition   of  Unpolluted   Water. 

XXVII. 

Eain  Water            ...             ..               .               39  samples 

XXVIII. 

Upland  Surface  Water         ..               .             195      „ 

XXIX. 

Deep  Well  Water  ...            ..              .             157      „ 

XXX. 

Spring  Water         ...             ..               .             198      „ 

. 

XXXI. 

Sea  Water              ...             ..               .               23      „ 

Sewage. 

XXXII. 

Average  from  15  <c  Midden  "  Towns  37  analyses 

XXXIII. 

Average  from  16  "  Water  Closet  "  Towns,  50  analyses     ... 

'" 
... 

XXXIV. 

Salford,  Wooden  Street  Sewer  March  15th  1869 

XXXV. 

Merthyr  Tydfil,  average  10  a.m.  to  5  p.m.,  Oct.  20th,  1871  1 



(after  treatment  with  lime)                                         ) 

... 

XXXVI. 

Ditto  Effluent  Water 

Ji 

§  89. 


NATURAL  WATERS  AND   SEWAGE. 


421 


in  parts  per  100,000. 


TABLE   8. 


Total 
solid 
Matter. 

Organic 
Carbon. 

Organic 
Nitro- 
gen. 

|°l& 
o 

Nitro- 
gen as 
Am- 
monia. 

Nitrogen 
as 
Nitrates 
and 
Nitrites. 

Total 
Inorganic 
Nitrogen. 

Total 
Combinec 
Nitrogen 

CMorine. 

Hardness. 

Tem- 
porary. 

Perma- 
nent. 

Total. 

1-52 

•132 

•014 

9'4 

0 

0 

0 

•014 

•50 

0 

1-5 

15 

2-94 

•148 

•016 

9-2 

0 

•005 

•005 

•022 

•64 

— 

— 

•9 

9-66 

•210 

•029 

7-2 

•002 

0 

•002 

•031 

T53 

•3 

3-7 

4-0 

V'OO 

•132 

•031 

4-1 

•002 

0 

•002 

•033 

•90 

0 

2-7 

2-7 

23-50 

•212 

•031 

6-8 

0 

•034 

•034 

•065 

1-40 

7-1 

12-9 

20-0 

11-16 

•418 

•059 

7-1 

•001 

•081 

•082 

•141 

1-75 

0 

6-0 

6-0 

30-92 

•432 

•080 

5-4 

•012 

•036 

•048 

•128 

3'10 

21-3 

5-3 

26-6 

31-00 

•041 

•008 

5-1 

0 

•362 

•362 

•370 

1-60 

18-4 

4-6 

23-0 

32-48 

•049 

•015 

3-3 

0 

•613 

•613 

•628 

1-90 

15-6 

10-1 

25-7 

540-20 

•340 

•105 

3-2 

•511 

14-717 

15-228 

15-333 

36-50 

27'5 

99-6 

127-1 

18-50 

1-200 

•126 

9-5 

•091 

0 

•091 

•217 

2-20 

2-0 

1-4 

3-4 

1.23-10 

•144 

•141 

1-0 

•181 

6-851 

7-032 

7-173 

12-85 

37-1 

40-0 

77-1 

U96-50 

•278 

•087 

3-2 

0 

25-840 

25-840 

25-927 

34-60 

26-7 

164-3 

191-0 

<  i.12-12 

•210 

•065 

3'2 

0 

5-047 

5-047 

5-112 

13-75 

14-3 

45-7 

60-0 

15-08 

•009 

•004 

2-2 

0 

•447 

•447 

•451 

1-30 

4-6 

5-1 

9-7 

'27-68 

•028 

•009 

3-1 

0 

•021 

•021 

•030 

1-55 

15-2 

6-0 

21-2 

1    8'80 

•015 

•003 

5-0 

— 

— 

— 

— 

— 

— 

— 

4-4 

,61/68 

•168 

•042 

4-0 

•007 

•066 

•073 

•115 

15-10 

3-4 

22 

5-6 

'  GS  00 

•127 

•029 

4-4 

•063 

2-937 

3-000 

3*029 

5-40 

27-9 

14-5 

42-4 

17-36 

•060 

•016 

3-7 

0 

•330 

•330 

•346 

2-45 

1-6 

10-0 

11-6 

30-20 

•048 

•018 

27 

0 

•833 

•833 

•851 

2-05 

17'1 

6-5 

23-6 

28-02 

•191 

•033 

5-8 

0 

•210 

•210 

•243 

1-68 

^  _ 



20-1 

28*99 

•134 

•025 

5-4 

0 

•226 

•226 

•251 

1-76 

— 

— 

20-9 

il-50 

•049 

•on 

4'5 

0 

•446 

•446 

•458 

2-47 

— 

— 

28-5 

14-40 

•059 

•014 

4'2 

•003 

•367 

•370 

•384 

1-70 

— 

— 

6'0 

41-39 

•068 

•016 

4'2 

•054 

•143 

•196 

•196 

2'85 

— 

— 

23-3 

26-01 

•245 

•054 

4-6 

•002 

•231 

•233 

•287 

1-73 

7-7 

8-8 

16-5 

2-95 

•070 

•015 

4'7 

•024 

•003 

•027 

•042 

•22 

__ 

_ 

•3 

9-67 

•322 

•032 

10-1 

•002 

•009 

•on 

•043 

1-13 

1-5 

4-3 

5'4 

13-78 

•061 

•018 

3'4 

•010 

•495 

•505 

•523 

5-11 

15-8 

9-2 

25-0 

;J8'20 

•056 

•013 

4'3 

•001 

•383 

•384 

•397 

2'49 

11-0 

7-5 

18-5 

*98'7 

•278 

•165 

1-7 

•005 

•033 

•038 

•203 

1975-6 

48-9 

748-0 

796-9 

Suspended  Matter. 
Mineral.  Organic.  Total. 

82-4 

4-181 

1-975 

2-1 

4-476 

0 

4-476 

6-451 

11-54 

17-81 

21-30 

39-11 

i    72-2 

4-696 

2-205 

2-1 

5-520 

•003 

5-523 

7-728 

10-66 

24-18 

20-51 

44-69 

;  119-6 

11-012 

7-634 

1-4 

5-468 

0 

5-468 

13-102 

20-50 

18-88 

26-44 

45-32 

j      rO'20 

1-282 

•952 

1-3 

1-054 

•052 

1-106 

2-058 

5-25 

7-88 

6-56 

14'44 

13-48 

•123 

•031 

4-0 

•048 

•300 

•348 

•379 

2-60 

Trace. 

422  VOLUMETRIC  ANALYSIS.  §    89. 

Total   Solid  Matter. 

Waters  which  leave  a  large  residue  on  evaporation  are,  as  a  rule,  less  suited 
for  general  domestic  purposes  than  those  which  contain  less  matter  in  solution, 
and  are  unfit  for  many  manufacturing  purposes.  The  amount  of  residue  is 
also  of  primary  importance  as  regards  the  use  of  the  water  for  steam  boilers, 
as  the  quantity  of  incrustation  produced  will  chiefly  depend  upon  it.  It  may 
vary  considerably,  apart  from  any  unnatural  pollution  of  the  water,  as  it 
depends  principally  on  the  nature  of  the  soil  through  or  over  which  the 
water  passes.  River  water,  when  but  slightly  polluted,  contains  generally 
from  10  to  40  parts.  Shallow  well  water  varies  greatly,  containing  from  30 
to  150  parts,  or  even  more,  as  in  examples  X.  and  XIII ,  the  proportion 
here  depending  less  on  the  nature  of  the  soil  than  on  the  original  pollution 
of  the  water.  Deep  well  water  also  varies  considerably ;  it  usually  contains 
from  20  to  VO  parts,  but  this  range  is  frequently  overstepped,  the  quantity 
depending  largely  upon  the  nature  of  the  strata  from  which  the  water  is 
obtained.  Example  XV.,  being  in  the  New  Eed  Sandstone,  has  a  small  pro- 
portion, but  XVII.  and  XVIII.  in  the  Chalk  have  a  much  larger  quantity. 
Spring  waters  closely  resemble  those  from  deep  wells.  Sewage  contains 
generally  from  50  to  100  parts,  but  occasionally  less,  and  frequently  much 
more,  as  in  example  XXXIV.  The  total  solid  matter,  as  a  rule,  exceeds  the 
sum  of  the  constituents  determined;  the  nitrogen,  as  nitrates  and  nitrites, 
being  calculated  as  potassic  nitrate,  and  the  chlorine  as  sodic  chloride ;  but 
occasionally  this  is  not  the  case,  owing,  it  is  likely,  to  the  presence  of  some  of 
the  calcium  as  calcic  nitrate  or  chloride. 

Organic   Carbon  or  Nitrogen. 

The  existing  condition  of  the  sample,  as  far  as  organic  contamination  is 
concerned,  must  be  inferred  from  the  amount  of  these  two  constituents.  In 
a  good  water,  suitable  -for  domestic  supply,  the  former  should  not,  under 
ordinary  circumstances,  exceed  0*2  and  the  latter  0'02  part. 

Waters  from  districts  containing  much  peat  are  often  coloured  more  or 
less  brown,  and  contain  an  unusual  quantity  of  organic  carbon,  but  this 
peaty  matter  is  probably  innocuous  unless  the  quantity  be  extreme.  The 
large  proportion  of  organic  carbon  and  nitrogen  given  in  the  average  for 
unpolluted  upland  surface  water  in  Table  8  (XXVIII.)  is  chiefly  due  to  the  fact 
that  upland  gathering  grounds  are  very  frequently  peaty.  The  examples 
given  (I.  to  V.)  may  be  taken  as  fairly  representative  of  the  character  of 
upland  surface  waters  free  from  any  large  amount  of  peaty  matter.  In 
surface  waters  from  cultivated  areas  the  quantity  of  organic  carbon  and 
nitrogen  is  greater,  owing  to  increased  density  of  population,  the  use  of 
organic  manures,  etc.,  the  proportion  being  about  0'25  to  0'3  part  of  organic 
carbon,  and  0'04  to  0'05  part  of  organic  nitrogen.  The  water  from  shallow 
wells  varies  so  widely  in  its  character  that  it  is  impossible  to  give  any  useful 
average.  In  many  cases,  as  for  example  in  XIII.  and  XIV.,  the  amount  is 
comparatively  small,  although  the  original  pollution,  as  shown  by  the  total 
inorganic  nitrogen  and  the  chlorides,  was  very  large ;  the  organic  matter  in 
these  cases  having  been  almost  entirely  destroyed  by  powerful  oxidation.  In 
VIII.  and  IX.  the  original  pollution  was  slight :  and  oxidation  being  active, 
the  organic  carbon  and  nitrogen  have  been  reduced  to  extremely  small 
quantities.  On  the  other  hand,  in  XI.  the  proportion  of  organic  matter  is 
enormous,  the  oxidizing  action  of  the  surrounding  soil  being  utterly 
insufficient  to  deal  with  the  pollution.  The  danger  attending  the  use  of 
shallow  well  waters,  which  contain  when  analyzed  very  small  quantities  of 
organic  matter,  arises  chiefly  from  the  liability  of  the  conditions  to  variation. 
Change  of  weather  and  many  other  circumstances  may  at  any  time  prevent 
the  purification  of  the  water,  which  at  the  time  of  the  analysis  appeared  to 
be  efficient.  Moreover,  it  is  by  no  means  certain,  that  an  oxidizing  action 


§    89.  NATURAL   WATERS   AND   SEWAGE.  423 

which  would  be  sufficient  to  reduce  the  organic  matter  in  a  water  to  a  very 
small  proportion,  would  be  equally  competent  to  remove  the  specific  poison  of 
disease.  Hence  the  greater  the  impurity  of  the  source  of  a  water  the  greater 
the  risk  attending  its  use. 

In  deep  well  waters  the  quantity  of  organic  carbon  and  nitrogen  also 
extends  through  a  wide  range,  but  is  generally  low,  the  average  being  about 
0*06  part  carbon  and  0'02  part  nitrogen  (XXIX.).  Here  the  conditions  are 
usually  very  constant,  and  if  surface  drainage  be  excluded,  the  source  of  the 
water  is  of  less  importance.  Springs  in  this,  as  in  most  other  respects, 
resemble  deep  wells ;  the  water  from  them  being  generally,  however,  some- 
what purer.  In  sewage  great  variations  are  met  with.  On  the  average  it 
contains  about  four  parts  of  organic  carbon  and  two  parts  of  organic  nitrogen 
(XXXII.  and  XXXIII.) ,  but  the  range  is  very  great.  In  the  table,  XXXIV. 
is  a  very  strong  sample,  and  XXXV.  a  weak  one.  The  effluent  water  from 
land  irrigated  with  sewage  is  usually  analogous  to  waters  from  shallow  wells, 
and  its  quality  varies  greatly  according  to  the  character  of  the  sewage  and 
the  conditions  of  the  irrigation. 

Ratio   of  Organic    Carbon   to    Organic   Nitrogen. 

The  ratio  of  the  organic  carbon  to  the  organic  nitrogen  given  in  the 
seventh  column  of  the  table  (which  shows  the  fourth  term  of  the  proportion 
— organic  nitrogen  :  organic  carbon  :  :  1  :  x),  is  of  great  importance  as 
furnishing  a  valuable  indication  of  the  nature  of  the  organic  matter  present. 
"When  this  is  of  vegetable  origin,  the  ratio  is  very  high,  and  when  of  animal 
origin  very  low.  This  statement  must,  however,  be  qualified,  on  account  of 
the  different  effect  of  oxidation  on  animal  and  vegetable  substances.  It  is 
found  that  when  organic  matter  of  vegetable  origin,  with  a  high  ratio  of 
carbon  to  nitrogen,  is  oxidized,  it  loses  carbon  more  rapidly  than  nitrogen,  so 
that  the  ratio  is  reduced.  Thus  unoxidized  peaty  waters  exhibit  a  ratio 
varying  from  about  8  to  20  or  even  more,  the  average  being  about  12 ; 
whereas,  the  ratio  in  spring  water  originally  containing  peaty  matter,  varies 
from  about  2  to  5,  the  average  being  about  3*2.  When  the  organic  matter  is 
of  animal  origin  the  action  is  reversed,  the  ratio  being  increased  by  oxidation. 
In  unpolluted  upland  surface  waters  the  ratio  varies  from  about  6  to  12,  but 
in  peaty  waters  it  may  amount  to  20  or  more.  In  surface  water  from 
cultivated  land  it  ranges  from  about  4  to  10,  averaging  about  6.  In  water 
from  shallow  wells  it  varies  from  about  2  to  8,  with  an  average  of  about  4,  but 
instances  beyond  this  range  in  both  directions  are  very  frequent.  In  water 
from  deep  wells  and  springs,  the  ratio  varies  from  about  2  to  6,  with  an 
average  of  4,  being  low  on  account,  probably,  of  the  prolonged  oxidation  to 
which  it  has  been  subjected,  which,  as  has  been  stated  above,  removes  carbon 
more  rapidly  than  nitrogen.  In  sea  water  this  action  reaches  a  maximum, 
the  time  being  indefinitely  prolonged,  and  the  ratio  is  on  the  average  about 
17.  This  is  probably  complicated  by  the  presence,  in  some  cases,  of  multitudes 
of  minute  living  organisms.  In  sewage  the  ratio  ranges  from  about  1  to  3, 
with  an  average  of  about  2. 

When,  in  the  case  of  a  water  containing  much  nitrogen  as  nitrates  and 
nitrites,  this  ratio  is  unusually  low,  incomplete  destruction  of  nitrates  during 
the  evaporation  may  be  suspected,  and  the  estimation  should  be  repeated. 
To  provide  for  this  contingency,  if  a  water  contain  any  considerable  quantity 
of  ammonia,  it  is  well,  when  commencing  the  evaporation  in  the  first 
instance,  to  set  aside  a  quantity  sufficient  for  this  repetition,  adding  to  it  the 
usual  proportion  of  sulphurous  acid. 

Nitrogen   as   Ammonia. 

The  ammonia  in  natural  waters  is  derived  almost  exclusively  from  animal 
contamination,  and  its  quantity  varies  between  very  wide  limits.  In  upland 


424  YOLUMETIUC  ANALYSIS.  §    89. 

surface  waters  it  seldom  exceeds  O'OOS  part,  the  average  being  about  0'002 
part.  In  water  from  cultivated  land  the  average  is  about  6'005,  and  the 
range  is  greater,  being  from  nil  to  0*025  part  or  even  more.  In  water  from 
shallow  wells  the  variation  is  so  great  that  it  would  be  useless  to  attempt  to 
state  an  average,  all  proportions  from  nil  to  as  much  as  2'  5  parts  having 
been  observed.  In  waters  from  deep  wells  a  very  considerable  proportion  is 
often  found,  amounting  to  O'l  part  or  even  more,  the  average  being  O'Ol 
part,  and  the  variations  considerable.  In  spring  water  it  is  seldom  that  more 
than  O'Ol  part  of  nitrogen  as  ammonia  occurs,  the  average  being  only  O'OOl 
part.  Sewage  usually  contains  from  2  to  6  parts,  but  occasionally  as  much 
as  9  or  10  parts,  the  average  being  about  five.  Ammonia  is  readily  oxidized 
to  nitrates  and  nitrites,  and  hence  its  presence,  in  considerable  quantity, 
usually  indicates  the  absence  of  oxidation,  and  is  generally  coincident  with 
the  presence  of  organic  matter.  That  sometimes  found  in  waters  from  very 
deep  wells  is,  however,  probably  due  to  subsequent  decomposition  of  nitrates. 

Nitrogen  as   Nitrates  and  Nitrites. 

Nitrates  and  nitrites  are  produced  by  the  oxidation  of  nitrogenous 
organic  matter,  and  almost  always  from  animal  matter.  In  upland  surface 
waters  the  proportion  varies  from  nil  to  0'05  part  or  very  rarely  more,  but 
the  majority  of  samples  contain  none  or  mere  traces  (I.  to  V.),  the  average 
being  about  0'009  part.  In  surface  waters  from  cultivated  land  the 
quantity  is  much  greater,  varying  from  nil,  which  seldom  occurs,  to  1  part, 
the  average  being  about  p'25  part.  The  proportion  in  shallow  wells  is  usually 
much  greater  still,  ranging  from  nil,  which  very  rarely  occurs,  to  as  much 
as  25  parts.  It  would  be  probably  useless  to  attempt  to  state  an  average,  but 
quantities  of  from  2  to  5  parts  occur  most  frequently.  In  water  from  deep 
wells  the  range  is  from  nil  to  about  3  parts,  and  occasionally  more,  the 
average  being  about  0'5  part.  In  spring  water  the  range  is  about  the  same 
as  in  deep  well  water,  but  the  average  is  somewhat  lower. 

It  sometimes  happens  that,  when  the  supply  of  atmospheric  oxygen  is 
deficient,  the  organic  matter  in  water  is  oxidized  at  the  expense  of  the 
nitrates  present ;  and  occasionally,  if  the  quantities  happen  to  be  suitably 
proportioned,  they  are  mutually  destroyed,  leaving  no  evidence  of  pollution. 
This  reduction  of  nitrates  often  occurs  in  deep  well  water,  as  for  example, 
in  that  from  wells  in  the  Chalk  beneath  London  Clay,  where  the  nitrates  are 
often  totally  destroyed.  In  sewages,  putrefaction  speedily  sets  in,  and 
during  this  condition  the  nitrates  are  rapidly  destroyed,  and  so  completely 
and  uniformly  that  it  is  probably  needless  to  attempt  their  estimation, 
except  in  sewages  which  are  very  weak,  or  for  other  special  reasons 
abnormal.  Out  of  a  large  number  of  samples,  only  a  very  few  have  been 
found  which  contained  any  nitrates,  and  those  only  very  small  quantities. 

Nitrites  occurring  in  deep  springs  or  wells  no  doubt  arise  from  the 
deoxidation  of  nitrates  by  ferrous  oxide,  or  certain  forms  of  organic  matter 
of  a  harmless  nature ;  but  whenever  they  occur  in  shallow  wells  or  river 
water,  they  may  be  of  much  greater  significance.  Their  presence  in  such 
cases  is  most  probably  due  to  recent  sewage  contamination,  and  such  waters 
must  be  looked  upon  with  great  suspicion. 

Total   Inorganic   Nitrogen. 

"When  organic  matter  is  oxidized  it  is  ultimately  resolved  into  inorganic 
substances.  Its  carbon  appears  as  carbonic  acid,  its  hydrogen  as  water,  and 
its  nitrogen  as  ammonia,  nitrous  acid,  or  nitric  acid ;  the  last  two  combining 
with  the  bases  always  present  in  water  to  form  nitrites  and  nitrates.  The 
carbon  and  hydrogen  are  thus  clearly  beyond  the  reach  of  the  analyst ;  but 
the  nitrogen  compounds,  as  has  been  shown,  can  be  accurately  determined, 
and  furnish  us  with  a  means  of  estimating  the  amount  of  organic  matter 


§    89.  NATURAL  WATERS   AND   SEWAGE.  425 

which  was  formerly  present  in  the  water,  but  which  has  already  undergone 
decomposition. 

The  sum  of  the  amounts  of  nitrogen  found  in  these  three  forms  con- 
stitutes then  a  distinct  and  valuable  term  in  the  analysis,  the  organic 
nitrogen  relating  to  the  present,  and  the  total  inorganic  nitrogen  to  the 
past  condition  of  the  water.  Since  ammonia,  nitrites,  and  nitrates  are  quite 
innocuous,  the  total  inorganic  nitrogen  does  not  indicate  actual  evil  like 
the  organic  nitrogen,  but  potential  evil,  as  it  is  evident  that  the  innocuous 
character  of  a  water  which  contains  much  nitrogen  in  these  forms  depends 
wholly  on  the  permanence  of  the  conditions  of  temperature,  aeration, 
nitration  through  soil,  etc.,  which  have  broken  up  the  original  organic 
matter;  if  these  should  at  any  time  fail,  the  past  contamination  would 
become  present,  the  nitrogen  appearing  in  the  organic  form,  the  water  being 
loaded  in  all  likelihood  with  putrescent  and  contagious  matter. 

In  upland  surface  waters  which  have  not  been  contaminated  to  any 
extent  by  animal  pollution  the  total  inorganic  nitrogen  rarely  exceeds  0'03 
part.  In  water  from  cultivated  districts  the  amount  is  greater,  ranging  as 
high  as  1  part,  the  average  of  a  large  number  of  samples  being  about  0'22  part. 
It  is  useless  to  attempt  any  generalization  for  shallow  wells,  as  the  pro- 
portion depends  upon  local  circumstances.  The  amount  is  usually  large  and 
may  reach,  as  seen  in  Example  XIII.,  the  enormous  quantity  of  twenty-five 
parts  per  100,000.  "Waters  containing  from  one  to  five  parts  are  very  commonly 
met  with.  In  water  from  deep  wells  and  springs,  quantities  ranging  up  to 
3*5  parts  have  been  observed,  the  average  on  a  large  series  of  analyses  being 
0'5  part  for  deep  wells  and  about  0'4  part  for  springs.  It  must  be  re- 
membered that  the  conditions  attending  deep  wells  and  springs  are 
remarkably  permanent,  and  the  amount  of  filtration  which  the  water  under- 
goes before  reaching  the  well  itself,  or  issuing  from  the  spring  is  enormous. 
Meteorological  changes  here  have  either  no  effect,  or  one  so  small  and  slow 
as  not  to  interfere  with  any  purifying  actions  which  may  be  taking  place. 
All  other  sources  of  water,  and  especially  shallow  wells,  are  on  the  other 
hand  subject  to  considerable  changes.  A  sudden  storm  after  drought  will 
wash  large  quantities  of  polluting  matter  into  the  water-course ;  or  dissolve 
the  filth  which  has  been  concentrating  in  the  pores  of  the  soil  during  the 
dry  season,  and  carry  it  into  the  well.  Small  indications  therefore  of  a 
polluted  origin  are  very  serious  in  surface  waters  and  shallow  well  waters, 
but  are  of  less  moment  in  water  from  deep  wells  and  springs ;  the  present 
character  of  these  being  of  chief  importance,  since  whatever  degree  of 
purification  may  be  observed,  may  usually  be  trusted  as  permanent.  The 
term  "total  inorganic  nitrogen"  has  been  chosen,  chiefly  because  it  is 
based  on  actual  results  of  analysis  without  the  introduction  of  any  theory 
whatever.  It  will  be  seen  that  it  corresponds  very  nearly  with  the  term 
"  previous  sewage  or  animal  contamination,"  which  was  introduced  by  Dr. 
F r an kl and,  and  which  was  employed  in  the  second  edition  of  this  work. 
Perhaps  few  terms  have  been  more  wonderfully  misunderstood  and  mis- 
represented than  that  phrase,  and  it  is  hoped  that  the  new  term  will  be  less 
liable  to  misconception.  It  will  be  remembered  that  the  "  previous  sewage 
contamination "  of  a  water  was  calculated  by  multiplying  the  sum  of  the 
quantities  of  nitrogen  present  as  ammonia,  nitrates,  and  nitrites,  by  10,000,  and 
deducting  320  from  the  product,  the  number  thus  obtained  representing  the 
previous  animal  contamination  of  the  water  in  terms  of  average  filtered 
London  sewage.  It  was  purely  conventional,  for  the  proportion  of  organic 
nitrogen  present  in  such  sewage  was  assumed  to  be  10  parts  per  100,000, 
whereas  in  the  year  1857  it  was  actually  8'4  parts,  and  in  1869  only  7  parts. 
The  deduction  of  320  was  made  to  correct  for  the  average  amount  of 
inorganic  nitrogen  in  rain  water,  and  this  is  omitted  in  calculating  "  total 
inorganic  nitrogen "  for  the  following  reasons  :— The  quantity  is  small, 
and  the  variations  in  composition  of  rain  water  at  different  times  and  under 
different  circumstances  very  considerable,  and  it  appears  to  obscure  the 


426  VOLUMETKIC  ANALYSIS.  §    89. 

significance  of  the  results  of  analysis  of  very  pure  waters  to  deduct  from 
all  the  same  fixed  amount.  As,  too,  the  average  amount  of  total  inorganic 
nitrogen  in  unpolluted  surface  waters  is  only  O'Oll  part  (XXVIII.),  it 
cannot  be  desirable  to  apply  a  correction  amounting  to  nearly  three  times 
that  average,  and  so  place  a  water  which  contains  0'032  part  of  total 
inorganic  nitrogen  on  the  same  level  as  one  which  contains  no  trace  of  any 
previous  pollution. 

Chlorine. 

This  is  usually  present  as  sodic  chloride,  but  occasionally,  as  has  been 
mentioned  before,  it  is  most  likely  as  a  calcic  salt.  It  is  derived,  in  some 
cases,  from  the  soil,  but  more  usually  from  animal  excreta  (human  urine 
contains  about  500  parts  per  100,000),  and  is  therefore  of  considerable 
importance  in  forming  a  judgment  as  to  the  character  of  a  water.  Un- 
polluted river  and  spring  waters  usually  contain  less  than  one  part ;  average 
town  sewage  about  eleven  parts.  Shallow  well  water  may  contain  any 
quantity  from  a  mere  trace  up  to  fifty  parts  or  even  more.  Its  amount  is 
scarcely  affected  by  any  degree  of  filtration  through  soil ;  thus,  the  effluent 
water  from  land  irrigated  with  sewage  contains  the  same  proportion  of 
chlorine  as  the  sewage,  unless  it  has  been  diluted  by  subsoil  water  or  con- 
centrated by  evaporation.  Of  course,  attention  should  be  given  to  the 
geological  nature  of  the  district  from  which  the  water  comes,  the  distance 
from  the  sea  or  other  source  of  chlorine,  etc.,  in  order  to  decide  on  the 
origin  of  the  chlorine.  Under  ordinary  circumstances,  a  water  containing 
more  than  three  or  four  parts  of  chlorine  should  be  regarded  with  suspicion. 

Hardness. 

This  is  chiefly  of  importance  as  regards  the  use  of  the  water  for  cleansing 
and  manufacturing  purposes,  and  for  steam  boilers.  It  is  still  a  moot  point 
as  to  whether  hard  or  soft  water  is  better  as  an  article  of  food.  The 
temporary  hardness  is  often  said  to  be  that  due  to  carbonates  held  in  solution 
by  carbonic  acid,  but  this  is  not  quite  correct ;  for  even  after  prolonged 
boiling,  water  will  still  retain  about  three  parts  of  carbonate  in  solution, 
and  therefore  when  the  total  hardness  exceeds  three  parts,  that  amount 
should  be  deducted  from,  the  permanent  hardness  and  added  to  the  temporary, 
in  order  to  get  the  quantity  of  carbonate  in  solution.  But  the  term 
" temporary"  hardness  properly  applies  to  the  amount  of  hardness  which 
may  be  removed  by  boiling,  and  hence,  if  the  total  hardness  be  less  than 
three  parts,  there  is  usually  no  temporary.  As  the  hardness  depends 
chiefly  on  the  nature  of  the  soil  through  and  over  which  the  water  passes, 
the  variations  in  it  are  very  great;  that  from  igneous  strata  has  least 
hardness,  followed  in  approximate  order  by  that  from  Metamorphic, 
Cambrian,  Silurian  and  Devonian  rocks,  Millstone  Grit,  London  Clay, 
Bagshot  Beds,  New  Bed  Sandstone,  Coal  Measures,  Mountain  Limestone, 
Oolite,  Chalk,  Lias,  and  Dolomite,  the  average  in  the  case  of  the  first 
being  2'4  parts,  and  of  the  last  41  parts.  As  animal  excreta  contain  a 
considerable  quantity  of  lime,  highly  polluted  waters  are  usually  extremely 
hard.  Water  from  shallow  wells  contains  varying  proportions  up  to  nearly 
200  parts  of  total  hardness  (XIII.).  No  generalization  can  be  made  as  to 
the  proportion  of  permanent  to  temporary  hardness. 

Suspended   Matter. 

This  is  of  a  less  degree  of  importance  than  the  matters  hitherto  considered. 
Prom  a  sanitary  point  of  view  it  is  of  minor  interest,  because  it  may  be  in 
most  cases  readily  and  completely  removed  by  filtration.  Mineral  suspended 
matter  is,  however,  of  considerable  mechanical  importance  as  regards  the 
formation  of  impediments  in  the  river  bed  by  its  gradual  deposition,  and 
as  regards  the  choking  of  the  sand  filters  in  water-works :  and  organic ' 


§    89.  NATUEAL  WATEKS  AND   SEWAGE.  427 

suspended  matter  is  at  times  positively  injurious,  and  always  favours  the 
growth  of  minute  organisms. 

From  the  determinations  which  have  been  described,  it  is  believed  that 
a  sound  judgment  as  to  the  character  of  a  water  may  be  made,  and  the 
analyst  should  hardly  be  content  with  a  less  complete  examination.  If, 
however,  from  lack  of  time  or  other  cause,  so  much  cannot  be  done, 
a  tolerably  safe  opinion  may  be  formed,  omitting  the  determination  of  total 
solid  matter,  and  organic  carbon  and  nitrogen.  But  it  must  not  be  forgotten 
that  by  so  doing  the  inquiry  is  limited  as  regards  organic  impurity,  to  the 
determination  of  that  which  was  formerly  present,  but  has  already  been 
converted  into  inorganic  substances.  If  still  less  must  suffice,  the  estimation 
of  nitrogen  as  nitrates  and  nitrites  may  be  omitted,  its  place  being  to 
a  certain  extent  supplied  by  that  of  chlorine,  but  especial  care  must  then  be 
taken  to  ascertain  the  source  of  the  latter  by  examination  of  the  district. 
If  it  be  in  any  degree  of  mineral  origin,  no  opinion  can  be  formed  from  it 
as  to  the  likelihood  of  organic  pollution.  At  best,  so  slight  an  examination 
must  be  of  but  little  value,  and  considering  the  rapidity  with  which  the 
nitrogen  as  nitrates  can  be  determined  by  the  indigo  process,  the  saving  of 
time  would  be  very  small. 

General   Considerations. 

In  judging  of  the  character  of  a  sample  of  water,  due  attention  must  of 
course  be  paid  to  the  purpose  for  which  it  is  proposed  to  be  used.  The 
analyst  frequently  has  only  to  decide  broadly  whether  the  water  is  good  or 
bad ;  as,  for  example,  in  cases  of  the  domestic  supply  to  isolated  houses  or  of 
existing  town  supplies.  Water  which  would  be  fairly  well  suited  for  the 
former  might  be  very  objectionable  for  the  latter,  where  it  would  be 
required  to  a  certain  extent  for  manufacturing  purposes.  Water  which 
would  be  dangerous  for  drinking  or  cooking  may  be  used  for  certain  kinds 
of  cleansing  operations';  but  it  must  not  be  forgotten,  that  unless  great  care 
and  watchfulness  are  exercised  there  is  considerable  danger  of  this  restriction 
being  neglected,  and  especially  if  the  objectionable  water  is  nearer  at  hand 
than  the  purer  supply.  There  would  for  this  reason,  probably,  be  some 
danger  attending  a  double  supply  on  a  large  scale  in  a  town,  even  if  the 
cost  of  a  double  service  of  mains,  etc.,  were  not  prohibitive. 

It  is  often  required  to  decide  between  several  proposed  sources  of  supply, 
and  here  great  care  is  necessary,  especially  if  the  differences  between  the 
samples  are  not  great.  If  possible,  samples  should  be  examined  at  various 
seasons  of  the  year ;  and  care  should  be  taken  that  the  samples  of  the  several 
waters  are  collected  as  nearly  as  possible  simultaneously  and  in  a  normal 
condition.  The  general  character  of  a  water  is  most  satisfactorily  shown  by 
the  average  of  a  systematic  series  of  analyses;  and  for  this  reason  the  average 
analysis  of  the  water  supplies  of  London,  taken  from  the  Reports  of  Dr. 
Prank  land  to  the  Registrar  General,  of  Glasgow  by  Dr.  Mills,  and  of 
Birmingham  by  Dr.  Hill,  are  included  in  the  table.  River  waters  should, 
as  a  rule,  not  be  examined  immediately  after  a  heavy  rain  when  they  are  in 
flood.  A  sudden  rainfall  after  a  dry  season  will  often  foul  a  river  more 
than  a  much  heavier  and  more  prolonged  downfall  after  average  weather. 
Similarly  the  sewage  discharged  from  a  town  at  the  beginning  of  a  heavy 
rainstorm  is  usually  extremely  foul,  the  solid  matter  which  has  been 
accumulating  on  the  sides  of  the  sewers,  and  in  corners  and  recesses,  being 
rapidly  washed  out  by  the  increased  stream. 

The  possibility  of  improvement  in  quality  must  also  be  considered.  A 
turbid  water  may  generally  be  rendered  clear  by  filtration,  and  this  will 
often  also  effect  some  slight  reduction  in  the  quantity  of  organic  matter ; 
but  while  somewhat  rapid  filtration  through  sand  or  similar  material  will 
usually  remove  all  solid  suspended  matter,  it  is  generally  necessary  to  pass 
the  water  very  slowly  through  a  more  efficient  material  to  destroy  any  large 


428  VOLUMETKIC  ANALYSIS.  §    89. 

proportion  of  the  organic  matter  in  solution.  Very  fine  sand,  animal 
charcoal,  and  spongy  iron  are  all  in  use  for  this  purpose.  The  quantity  of 
available  oxygen  must  not  be  neglected  in  considering  the  question  of 
filtration.  If  the  water  contains  only  a  small  quantity  of  organic  matter 
and  is  well  aerated,  the  quantity  of  oxygen  in  solution  may  be  sufficient, 
and  the  filtration  may  then  be  continuous;  but  in  many  instances  this 
is  not  the  case,  and  it  is  then  necessary  that  the  filtration  should  be 
intermittent,  the  water  being  allowed  at  intervals  to  drain  off  from  the 
filtering  material  in  order  that  the  latter  may  be  well  aerated,  after  which  it 
is  again  fit  for  work. 

Softening  water  by  Clark's  process  generally  removes  a  large  quantity 
of  organic  matter  (see  Table  8,  XVI.)  from  solution,  it  being  carried  down 
with  the  calcic  carbonate  precipitate. 

It  is  evident  that  no  very  definite  distinction  can  be  drawn  between  deep 
and  shallow  wells.  In  the  foregoing  pages,  deep  wells  generally  mean  such 
as  are  more  than  100  feet  deep,  but  there  are  many  considerations  which 
qualify  this  definition.  A  deep  well  may  be  considered  essentially  as  one 
the  water  in  which  has  filtered  through  a  considerable  thickness  of  porous 
material,  and  whether  the  shaft  of  such  a  well  is  deep  or  shallow  will  depend 
on  circumstances.  If  the  shaft  passes  through  a  bed  of  clay  or  other 
impervious  stratum,  and  the  surface  water  above  that  is  rigidly  excluded,  the 
well  should  be  classed  as  "  deep,"  even  if  the  shaft  is  only  a  very  few  feet  in 
depth,  because  the  water  in  it  must  have  passed  for  a  considerable  distance 
below  the  clay.  On  the  other  hand,  however  deep  the  shaft  of  a  well,  it 
must  be  considered  as  "shallow"  if  water  can  enter  the  shaft  near  the 
surface,  or  if  large  cracks  or  fissures  give  free  passage  for  surface  water 
through  the  rock  in  which  the  well  is  sunk.  With  these  principles  in  view, 
the  water  from  wells  may  often  be  improved.  Every  care  should  be  taken 
to  exclude  surface  water  from  deep  wells;  that  is  to  say,  all  water  from 
strata  within  about  100  feet  from  the  surface  or  above  the  first  impervious 
bed.  In  very  deep  wells  which  pass  through  several  such  beds,  it  is  desirable 
to  examine  the  water  from  each  group  of  pervious  strata,  as  this  often  varies 
in  quality,  and  if  the  supply  is  sufficient,  exclude  all  but  the  best. 

In  shallow  wells  much  may  occasionally  be  accomplished  in  a  similar 
manner  by  making  the  upper  part  of  the  shaft  water-tight.  It  is  also 
desirable  that  the  surface  for  some  distance  round  the  well  should  be  puddled 
with  clay,  concreted,  or  otherwise  rendered  impervious,  so  as  to  increase  the 
thickness  of  the  soil  through  which  the  water  has  to  pass.  Drains  passing 
near  the  well  should  be,  if  possible,  diverted ;  and  of  course  cesspools  should 
be  either  abolished,  or,  if  that  is  impracticable,  removed  to  as  great 
a  distance  from  the  well  as  is  possible,  and  in  addition  made  perfectly 
water-tight.  Changes  such  as  these  tend  to  diminish  the  uncertainty  of  the 
conditions  attending  a  shallow  well,  but  in  most  cases  such  a  source  of 
supply  should,  if  possible,  be  abandoned  as  dangerous  at  best. 

Clark's   Process   for   Softening   Hard  Water. 

The  patent  right  of  this  process  having  expired,  the  public  are  free  to  use  it. 

This  method  of  softening  consists  in  adding  lime  to  the  hard  water.  It  is 
only  applicable  to  water  which  owes  its  hardness  entirely,  or  chiefly,  to  the 
calcic  and  magnesic  carbonates  held  in  solution  by  carbonic  acid  (temporary 
hardness}.  Water  which  owes  its  hardness  to  calcic  or  magnesic  sulphate 
(permanent  hardness')  cannot  be  thus  softened ;  but  any  water  which  softens 
on  boiling  for  half  an  hour  will  be  softened  to  an  equal  extent  by  Clark's 
process.  The  hard  water  derived  from,  chalk,  limestone,  or  oolite  districts,  is 
generally  well  adapted  for  this  operation. 

To  soften  700  gallons  of  water,  about  one  ounce  of  quicklime  is  required 
for  each  part  of  temporary  hardness  in  100,000  parts  of  water.  The  quantity 
of  quicklime  required  is  thoroughly  slaked  in  a  pailful  of  water.  Stir  up 


§    90.  NATURAL  WATERS   AND   SEWAGE.  429 

the  milk  of  lirne  thus  obtained,  and  pour  it  immediately  into  the  cistern 
containing  at  least  50  gallons  of  the  water  to  be  softened,  taking  care  to 
leave  in  the  pail  any  heavy  sediment  that  may  have  settled  to  the  bottom  in 
the  few  seconds  that  intervened  between  the  stirring  and  pouring.  Fill  the 
pail  again  with  water,  and  stir  and  pour  as  before.  The  remainder  of  the 
700  gallons  of  water  must  then  be  added,  or  allowed  to  run  into  the  cistern 
from  the  supply  pipe.  If  the  rush  of  the  water  does  not  thoroughly  mix 
the  contents  of  the  cistern,  this  must  be  accomplished  by  stirring  with 
a  suitable  wooden  paddle.  The  water  will  now  appear  very  milky,  owing  to 
the  precipitation  of  the  chalk  which  it  previously  contained  in  solution 
together  with  an  equal  quantity  of  chalk  which  is  formed  from  the  quick- 
lime added. 

After  standing  for  three  hours  the  water  will  be  sufficiently  clear  to  use 
for  washing;  but  to  render  it  clear  enough  for  drinking,  at  least  twelve 
hours'  settlement  is  required.  This  process  not  only  softens  water,  but  it 
removes  to  a  great  extent  objectionable  organic  matter  present. 

The  proportion  of  lime  to  water  may  be  more  accurately  adjusted  during 
the  running  in  of  the  hard  water,  by  taking  a  little  water  from  the  cistern 
at  intervals  in  a  small  white  cup,  and  adding  to  it  a  drop  or  two  of  solution 
of  nitrate  of  silver,  which  will  produce  a  yellow  or  brownish  colouration  as 
long  as  there  is  lime  present  in  excess.  As  soon  as  this  becomes  very  faint, 
and  just  about  to  disappear,  the  flow  of  water  must  be  stopped.  The 
carbonate  may  be  removed  by  filtration  in  a  very  short  time  after  the  addition 
of  lime,  and  on  the  large  scale  this  may  be  done  with  great  rapidity  by 
means  of  a  filter  press,  as  in  Porter's  process.  This  latter  method  of 
rapidly  softening  and  purifying  water  is  the  invention  of  J.  Henderson 
Porter,  C.E.,  Queen  Victoria  Street,  London,  whose  apparatus  is  largely 
in  use  for  public  water  supplies,  and  for  softening  waters  used  in 
manufacturing  processes,  and  the  prevention  of  boiler  incrustations,  etc. 
The  chief  objections  to  the  original  Clark  process  are,  the  large  space  required 
for  mixing  and  settling  tanks,  and  the  time  required  for  subsidence  of  the 
precipitate.  On  the  contrary,  in  Porter's  process,  the  space  occupied  is 
small,  and  the  clarification  immediate.  The  results  are  admirable,  and  are 
achieved  at  a  very  moderate  cost. 

Another  apparatus  devised  by  M.M.  Gaillet  and  Hiiet,  of  Lille,  consists 
of  a  lofty  tank  containing  a  series  of  sloping  troughs.  The  water  after 
mixing  with  the  due  proportion  of  lime  water  passes  slowly  downwards 
through  the  tank  and  deposits  all  the  carbonate  precipitate  in  the  troughs, 
from  which  it  can  be  run  off  as  mud.  The  process  is  thus  continuous  and 
very  convenient  in  dealing  with  large  volumes  of  water. 


METHODS  OF  ESTIMATING  THE  ORGANIC   IMPURITIES   IN 
WATER   WITHOUT    GAS   APPARATUS. 

§  90.  THE  foregoing  methods  of  estimating  the  organic 
impurities  in  potable  waters,  though  very  comprehensive  and 
trustworthy,  yet  possess  the  disadvantage  of  occupying  a  good  deal 
of  time,  and  necessitate  the  use  of  a  complicated  and  expensive  set 
of  apparatus,  which  may  not  always  be  within  the  reach  of  the 
operator. 

No  information  of  a  strictly  reliable  character  as  to  the  nature  of  the 
organic  matter  or  its  quantity  can  be  gained  from  the  use  of  standard 
permanganate  solution  as  originally  devised  by  Forschammer, 
and  the  same  remark  applies  to  the  loss  on  ignition  of  the  residue, 
both  of  which  have  been  in  past  time  largely  used. 


430  VOLUMETRIC   ANALYSIS.  §    90. 

The  Forscliammer  or  oxygen  process,  however,  as  improved  by 
Letheby,  and  further  elaborated  by  Tidy,  may  be  considered  as 
worthy  of  considerable  confidence  in  determining  the  amount  of 
organic  substances  contained  in  a  water. 


The   Oxygen   Process. 

This  process  depends  upon  the  estimation  of  the  amount  of 
oxygen  required  to  oxidize  the  organic  and  other  oxidizable  matters 
in  a  known  volume  of  water,  slightly  acidified  with  pure  sulphuric 
acid.  For  this  purpose,  a  standard  solution  of  potassic  permanganate 
is  employed  in  excess.  The  amount  of  unchanged  permanganate, 
after  a  given  time,  is  ascertained  by  means  of  a  solution  of  sodic 
hyposulphite,  by  the  help  of  the  iodine  and  starch  reaction. 

Tidy  and  Frank  land  in  all  cases  make  a  blank  experiment 
with  pure  distilled  water,  side  by  side  with  the  sample. 

As  regards  the  time  during  which  the  sample  of  water  should  be 
exposed  to  the  action  of  the  permanganate,  authorities  somewhat 
differ.  It  is  manifest  that,  if  the  water  contains  certain  reducing 
agents  such  as  nitrites,  ferrous  salts,  or  sulphuretted  hydrogen,  an 
immediate  reduction  of  the  reagent  will  occur,  and  Tidy  is 
disposed  to  register  the  reduction  which  occurs  in  three  minutes,  in 
the  known  absence  of  iron  and  sulphuretted  hydrogen,  as  due  to 
nitrites.  The  same  authority  adopts  the  plan  of  making  two 
observations,  one  at  the  end  of  one  hour  and  another  at  the  end  of 
three  hours,  at  the  ordinary  temperature  of  the  laboratory  (say  60° 
Fahr.  or  16°  C.). 

Frankland  admits  this  process  to  be  the  best  volumetric  method 
in  existence  for  the  estimation  of  organic  matters,  but  is  content  with 
one  experiment  lasting  three  hours  (also  at  ordinary  temperature). 

The  Water  Committee  of  the  Society  of  Public  Analysts  of 
Great  Britain  and  Ireland  have  adopted  the  periods  of  fifteen 
minutes  and  four  hours  for  the  duration  of  the  experiment,  at  the 
fixed  temperature  of  80°  Fahr.  or  27°  C.* 

*Dupre"  in  further  comment  on  the  temperature  at  which  it  is  advisable  to  carry 
out  this  method  (Analyst,  x.  118),  and  also  as  to  the  reactions  involved,  points  out  one 
feature  which  has  in  all  probability  impressed  itself  upon  other  operators,  that  is  to 
say,  the  effect  of  chlorides  when  present  in  any  quantity.  It  is  evident  that  if  in  this 
case  the  permanganate  is  used  at  a  high  temperature  and  in  open  vessels,  chlorine  will 
be  liberated ;  part  escaping  into  the  air,  and  the  rest  nullifying  the  reducing  effect  of 
any  organic  matter  present  on  the  permanganate.  If,  however,  the  experiment  be 
conducted  at  high  temperature  in  a  closed  vessel,  the  probable  error  is  eliminated, 
because  the  chlorine  is  retained,  and  subsequently,  when  cool  and  the  potassic  iodide 
added,  the  free  Cl  liberates  exactly  the  same  amount  of  iodine  as  would  have  been  set 
free  by  the  permanganate  from  which  it  was  produced.  It  thus  becomes  possible  to 
estimate  the  amount  of  oxidizable  organic  matter,  even  in  sea  water.  In  oi'der,  how- 
ever, to  reduce  the  probable  error  from  the  presence  of  chlorides,  Dupr^  prefers  to 
carry  on  the  experiment  at  a  very  low  temperature,  in  fact,  as  near  0°  C.  or  32°  F.  as 
possible,  and  uses  phosphoric  acid  in  place  of  sulphuric  (250  gm.  glacial  acid  to  the 
liter;  10  c.c.  of  which  is  used  for  each  quarter  or  half  liter  of  water).  The  sample  is 
cooled,  the  reagent  added  in  a  stoppered  bottle,  and  kept  in  an  ordinary  refrigerator 
for  twenty-four  hours.  The  same  operator  very  rightly  condemns  the  practice  adopted 
by  some  chemists,  especially  those  of  Germany,  of  boiling  a  water  with  permanganate 
and  sulphuric  acid.  The  presence  of  chlorides  in  varying  proportions  must  in  such 
case  totally  vitiate  the  results. 


§    90.  NATURAL  WATERS   AND   SEWAGE.  431 

Dupre  has  carried  out  experiments  (Analyst,  vii.  1),  the 
results  of  which  are  in  favour  of  the  modifications  adopted  by  the 
Committee.  The  chief  conclusions  arrived  at -are — 

(1)  That,  practically,  no  decomposition  of  permanganate  takes 
place  during  four  hours  when  digested  in  a  closed  vessel  at  80° 
with    perfectly    pure   water    and   the   usual   proportion    of   pure 
sulphuric  acid. 

By  adopting  the  closed  vessel,  all  dust  or  reducing  atmospheric 
influence  is  avoided. 

(2)  The  standardizing  of  the  hyposulphite  and  permanganate, 
originally  and  from  time  to  time,  must  be  made  in  a  closed  vessel 
in  the  same  manner  as  the  analysis  of  a  water,  since  it  has  been 
found  that  when  the  titration  is  made  slowly  in  an  open  beaker 
less  hyposulphite  is  required  than  in  a  stoppered  bottle.     This  is 
probably  due  to  a  trifling  loss  of  iodine  by  evaporation. 

(3)  That   with   very   pure  waters    no    practical    difference    is 
produced  by  a  rise  or  fall  of  temperature,  the  same  results  being 
obtained  at  32°  F.  as  at  80°  F.     On  the  other  hand,  with  polluted 
waters,  the  greater  the  organic  pollution,  the  greater  the  difference 
in  the  amount  of  oxygen  absorbed  according  to  temperature. 

(4)  As  to  time,  it  appears  that  very  little  difference  occurs  in 
good  waters  between  three  and  four  hours'  digestion  ;  but  with  bad 
waters  there  is  often  a  very  considerable  increase  in  the  extra  hour ; 
and  thus  Dupre  doubts  whether  even  four  hours'  digestion  suffices 
for  very  impure  waters. 

The  necessary  standard  solutions  for  working  the  process  will  be 
described  further  on. 

Comparison  of  the  Results  of  this  Process  with,  the  Combustion 
Method. — I  cannot  do  better  than  quote  Dr.  Frankland's  remarks 
on  this  subject,  as  contained  in  his  treatise  on  Water  Analysis : — 

"  The  objections  to  the  oxygen  process  are,  first,  that  its  indications  are 
only  comparative,  and  not  absolute ;  and,  second,  that  its  comparisons  are 
only  true  when  the  organic  matter  compared  is  substantially  identical  in 
composition. 

"  For  many  years,  indeed,  after  this  process  was  first  introduced,  the  action 
of  the  permanganate  of  potash  was  tacitly  assumed  to  extend  to  the  complete 
oxidation  of  the  organic  matter  in  the  water,  and,  therefore,  the  result  of  the 
experiment  was  generally  stated  as  'the  amount  of  oxygen  required  to 
oxidize  the  organic  matter ; '  whilst  some  chemists  even  employed  the  number 
so  obtained  to  calculate  the  actual  weight  of  organic  matter  in  the  water  on 
the  assumption  that  equal  weights  of  all  kinds  of  organic  matter  required 
the  same  weight  of  oxygen  for  their  complete  oxidation. 

"Both  these  assumptions  have  been  conclusively  proved  to  be  entirely 
fallacious,  for  it  has  been  experimentally  demonstrated  by  operating  upon 
known  quantites  of  organic  substances  dissolved  in  water,  that  there  is  no 
relation  either  between  the  absolute  or  relative  weight  of  different  organic 
matters  and  the  oxygen  which  such  matters  abstract  from  permanganate  of 
potash. 


432 


VOLUMETRIC   ANALYSIS. 


§    90. 


"Nevertheless,  in  the  periodical  examination  of  waters  from  the  same 
source,  I  have  noticed  a  remarkable  parallelism  between  the  proportions  of 
organic  carbon  and  of  oxygen  abstracted  from  permanganate  of  potash. 
Thus,  for  many  years  past,  I  have  seen  in  the  monthly  examination  of  the 
waters  of  the  Thames  and  Lea  supplied  to  London  such  a  parallelism  between 
the  numbers  given  by  Dr.  Tidy,  expressing  '  oxygen  consumed,'  and  those 
obtained  by  myself  in  the  determination  of  '  organic  carbon.' 

"  This  remarkable  agreement  of  the  two  processes,  extending  as  it  did  to 
1,418  out  of  1,686  samples,  encouraged  me  to  hope  that  a  constant  multiplier 
might  be  found,  by  which  the  '  oxygen  consumed 'of  the  Porschammer 
process  could  be  translated  into  the  'organic  carbon'  of  the  combustion 
method  of  analysis.  To  test  the  possibility  of  such  a  conversion,  my  pupil, 
Mr.  Woodland  Toms  made,  at  my  suggestion,  the  comparative  experi- 
ments recorded  in  the  following  tables : — 


1.— River  "Water. 


Source  of  Sample. 

Oxygen           C       _ 
consumed.          O 

Organic 
carbon  by 
combustion. 

Chelsea  Company's  supply    ... 

0*098    x    2'6     = 

0-256 

West  Middlesex  Co.'s  „         

0*116    x    2'5     = 

0-291 

Lambeth  Co.'s              „ 

0-119    x    2-43  = 

0-282 

Southwark  Co.'s          „         

0-121    x    2-22  = 

0-269 

New  River  Co.'s          „ 

0-076    x    2'4     = 

0-183 

Chelsea  Co.'s  second  sample  ... 

0-070   x   2'69  = 

0-188 

Lambeth  Co.'s          „ 

0-119   x    1-99  = 

0-234 

New  River  Co.'s      „            

0-107   x   2-25  = 

0-221 

"  As  the  result  of  these  experiments,  the  average  multiplier  is  2' 38,  and 
the  maximum  errors  incurred  by  its  use  would  be  —  0'021  part  of  organic 
carbon  in  the  case  of  the  second  sample  of  the  Chelsea  Company's  water, 
and  +0'049  part  in  that  of  the  second  sample  of  the  Lambeth  Company's 
water.  These  errors  would  practically  have  little  or  no  influence  upon  the 
analyst's  opinion  of  the  quality  of  the  water.  It  is  desirable  that  this 
comparison  should  be  extended  to  the  water  of  other  moderately  polluted 
rivers. 

II.— Deep   Well  Water. 


Source  of  Sample. 

Oxygen 
consumed. 

C 
O 

Organic 
carbon  by 
combustion. 

Kent  Company's  supply        
Colne  Valley  Co.'s  „ 
Hodgson's  Brewery  well       

0-015     x 
0-0135   x 
0-03        x 

5-1  = 
6-9  = 
5'3  = 

0-077 
0-094 
0-158 

"  The  relation  between  '  oxygen  consumed '  and  '  organic  carbon '  in  the 
case  of  deep  well  waters  is  thus  very  different  from  that  which  obtains  in  the 
case  of  river  waters,  and  the  average  multiplier  deduced  from  the  foregoing 
examples  is  5'8,  with  maximum  errors  of +0*01  of  organic  carbon  in  the  case 
of  the  Kent  Company's  water,  and  —  G'015  in  that  of  the  Colne  Valley 
water.  Such  slight  errors  are  quite  unimportant. 

"Similar  comparative  experiments  made  with  shallow  well  and  upland 


§    90.  NATURAL  WATERS    AND    SEWAGE.  433 

surface  waters  showed  amongst  themselves  a  wider  divergence,  but  pointed 
to  an  average  multiplier  of  2'28  for  shallow  well  water,  approximately  the 
same  as  that  found  for  moderately  polluted  river  water,  and  1'8  for  upland 
surface  water. 

"  In  the  interpretation  of  the  results  obtained,  either  by  the  Forschammer 
or  combustion  process,  the  adoption  of  a  scale  of  organic  purity  is  often  useful 
to  the  analyst,  although  a  classification  according  to  such  a  scale  may  require 
to  be  modified  by  considerations  derived  from  the  other  analytical  data.  It 
is  indeed  necessary  to  have  a  separate  and  more  liberal  scale  for  upland  surface 
water,  the  organic  matter  of  which  is  usually  of  a  very  innocent  nature,  and 
derived  from  sources  precluding  its  infection  by  zymotic  poisons. 

"  Subject  to  modification  by  the  other  analytical  data,  the  following  scale  of 
classification  has  been  suggested  by  Dr.  Tidy  and  myself: — 

Section   I.— Upland   Surface   "Water. 

"  Class  I.  Water  of  great  organic  purity,  absorbing  from  permanganate 
of  potash  not  more  than  O'l  part  of  oxygen  per  100,000  parts  of  water,  or  0'07 
grain  per  gallon. 

"  Class  II.  Water  of  medium  purity,  absorbing  from  O'l  to  0'3  part  of 
oxygen  per  100,000  parts  of  water,  or  0'07  to  0'21  grain  per  gallon. 

"  Class  III.  Water  of  doultful  purity,  absorbing  from  0'3  to  0'4  part  per 
100,000,  or  0'21  to  0'28  grain  per  gallon. 

"  Class  IV.  Impure  water,  absorbing  more  than  0'4  part  per  100,000,  or 
0'28  grain  per  gallon. 

Section   II.— Water   other   than    Upland   Surface. 

"  Class  I.  Water  of  great  organic  purity,  absorbing  from  permanganate 
of  potash  not  more  than  0'05  part  of  oxygen  per  100,000  parts  of  water,  or 
0*035  grain  per  gallon. 

"  Class  II.  Water  of  medium  purity,  absorbing  from  0'05  to  0'15  part 
of  oxygen  per  100,000,  or  0'035  to  O'l  grain  per  gallon. 

"  Class  III.  Water  of  doubtful  purity,  absorbing  from  0'15  to  0'2  part 
of  oxygen  per  100,000,  or  O'l  to  0'15  grain  per  gallon. 

"  Class  IV.  Impure  water,  absorbing  more  than  0'2  part  of  oxygen 
per  100,000,  or  0'15  grain  per  gallon." 

The   Albuminoid  Ammonia   Process. 

"Wanklyn,  Chapman,  and  Smith  are  the  authors  of  this  well- 
known  method  of  estimating  the  quantity  of  nitrogenous  organic 
matter  in  water,  which  depends  upon  the  conversion  of  the  nitrogen 
in  such  organic  matter  into  ammonia,  when  distilled  with  an  alkaline 
solution  of  potassic  permanganate  (/.  C.  S.  1867,  591). 

The  authors  have  given  the  term  "Albuminoid  ammonia"  to 
the  NH3  produced  from  nitrogenous  matter  by  the  action  of  the 
permanganate,  doubtless  because  the  first  experiments  made  in  the 
process  were  made  with  albuminous  substances;  but  the  authors 
also  proved  that  ammonia  may  be  obtained  in  a  similar  way  from 
a  great  variety  of  nitrogenous  organic  substances,  such  as  hippuric 
acid,  narcotine,  strychnine,  morphine,  creatine,  gelatine,  casein,  etc. 
Unfortunately,  however,  although  the  proportion  of  nitrogen 

F   F 


434  VOLUMETRIC  ANALYSIS.  §    90. 

yielded  by  any  one  substance  when  treated  with  boiling  alkaline 
permanganate  appears  to  be  definite,  yet  different  substances  give 
different  proportions  of  their  nitrogen.  Thus  hippuric  acid  and 
narcotine  yield  the  whole,  but  strychnine  and  morphine  only  one- 
half  of  their  known  proportion  of  nitrogen.  Hence  the  value  of  the 
numerical  results  thus  obtained  depends  entirely  on  the  assumption 
that  the  nitrogenous  organic  matter  in  water  is  uniform  in  UK 
nature,  and  the  authors  say  that  in  a  river  polluted  mainly  by 
sewage  "the  disintegrating  animal  refuse  would  be  pretty  fairly 
measured  by  ten  times  the  albuminoid  ammonia  which  it  yields." 

It  is  stated  by  the  authors  that  the  albuminoid  ammonia  from  a 
really  good  drinking  water  should  not  exceed  O'OOS  part  in  100,000. 
The  average  of  fifteen  samples  of  Thames  water  supplied  to  London 
by  the  various  Water  Companies  in  1867  was  0*0089,  and  in  five 
samples  supplied  by  the  New  Kiver  Company  0'0068  part  per 
100,000. 

The  necessary  standard  solutions  and  directions  for  working  the 
process  will  be  described  further  on  (page  437). 


The   Kjeldahl   Method  for   Organic   Nitrogen  in  Waters. 

This  method  has  been  used  by  Drown  and  Martin  (C.  N.  lix. 
272)  with  apparent  success.  These  operators  found  that  the 
presence  of  nitrates  and  nitrites,  as  occurring  in  ordinary  waters, 
did  not  interfere  with  the  accurate  estimation  of  the  organic 
nitrogen,  probably  owing  to  the  state  of  dilution  occurring  in 
waters.  The  accuracy  of  the  method  was  tested  by  known 
weights  of  ammonia,  urea,  uric  acid  and  napthylamine,  but  no 
comparison  of  the  results  with  waters  was  made  side  by  side  with 
the  combustion  method. 

The  Analysis :  500  c.c.  of  the  water  is  poured  into  a  round-bottom  flask 
of  about  900  c.o.  capacity,  and  boiled  until  200  c.c.  have  been  distilled  off. 
The  free  ammonia  which  is  thus  expelled  may,  if  desired,  be  determined  by 
connecting  the  flask  with  a  condenser.  To  the  remaining  water  in  the  flask 
is  added,  after  cooling,  10  c.c.  of  pure  concentrated  sulphuric  acid.  After 
shaking,  the  flask  is  placed  in  an  inclined  position  on  wire  gauze,  on  a  ring- 
stand,  or  other  convenient  support,  and  boiled  cautiously,  in  a  good-drawing 
hood,  until  all  the  water  is  driven  off  and  the  concentrated  sulphuric  acid  is 
white  or  a  very  pale  yellow.  The  flask  is  then  removed  from  the  flame,  and 
a  very  little  powdered  permanganate  added  until,  on  shaking,  the  liquid 
acquires  a  green  colour,  showing  that  an  excess  of  the  permanganate  has  been 
added.  Should  the  colour  be  purple  instead  of  green,  it  shows  that  the  water 
has  not  all  been  driven  off.  After  cooling,  200  c.c.  of  water  free  from 
ammonia  are  added,  the  neck  of  the  flask  being  washed  free  from  acid,  and 
then  100  c.c.  of  sodic  hydrate  *  solution.  The  flask  is  immediately  connected 
with  the  condenser,  and  then  shaken  to  mix  the  contents. 

*  The  sodic  hydrate  solution  is  made  by  dissolving  200  gm.  of  commercial  caustic 
soda  of  good  quality  in  1'25  liters  of  distilled  water,  adding  2  gm.  of  potassic  per- 
manganate, and  hoiling  down  to  somewhat  less  than  a  liter.  When  cold,  the  solution 
is  made  up  to  a  liter.  The  addition  of  the  permanganate  is  to  oxidize  any  organic 
matter  which  may  be  present  in  the  caustic  soda. 


§    91.  NATURAL  WATERS  AND   SEWAGE.  435 

The  distillation  at  the  start  is  conducted  rather  slowly,  and  the  first  50  c.c. 
are  condensed  in  very  dilute  hydrochloric  acid.  The  contents  of  the  flask 
may  then  be  boiled  more  rapidly  until  150  c.c.  to  175  c.c.  have  altogether 
been  collected.  The  total  distillate  is  made  up  to  250  c.c.  with  water  free 
from  ammonia,  well  mixed,  and  50  c.c.  taken  for  Nesslerization.  No  serious 
difficulty  has  been  encountered  from  bumping  when  boiling  the  alkaline 
solution.  The  use  of  metallic  zinc  in  the  flask  to  facilitate  the  boiling  is,  of 
course,  inadmissible,  on  account  of  the  reduction  of  nitrates  and  nitrites, 
should  they  be  present,  to  ammonia. 

Before  beginning  a  determination  the  water  in  the  flask  is  boiled  until  the 
distillate  shows,  on  Nesslerization,  that  the  apparatus  is  completely  free  from 
ammonia.  Into  the  flask  which  receives  the  distillate  there  is  put  1  c.c.  of 
the  dilute  hydrochloric  acid  and  50  c.c.  of  water.  The  delivery  tube  dips 
into  this  liquid  only  during  the  collection  of  the  first  50  c.c.  of  the  distillate. 
The  flask  is  then  lowered  so  that  the  tube  remains  above  the  liquid  for  the 
remaining  time  of  the  distillation. 

In  carrying  out  the  operation,  the  most  scrupulous  care  must  be  observed 
in  preventing  access  of  ammonia  from  any  source.  The  acid  solutions  will 
absorb  ammonia  from  the  air  of  the  laboratory  or  from  the  dust  of  the  room 
if  they  are  allowed  to  remain  uncovered  for  any  length  of  time.  This  source 
of  error  has  been  found  at  times  to  be  very  large ;  quite  enough  to  render  a, 
determination  valueless.  One  experiment  gave  a  gain  of  ammonia  in  twenty 
hours,  by  leaving  the  flask  which  contained  the  concentrated  sulphuric  acid 
uncovered,  equivalent  to  0*5  c.c.  of  the  standard  ammonic  chloride  solution, 
and  at  another  time  the  gain  was  3  c.c. 

The  operation  should  therefore  be  carried  out  without  interruption,  and  for 
every  determination,  or  set  of  determinations,  a  blank  analysis  with  ammonia- 
free  water  should  be  made  for  a  correction  for  the  ammonia  in  the  reagents 
and  that  accidentally  introduced  in  the  process. 

Other  methods  of  estimating  the  organic  constituents  in  Drinking 
"Waters  are  the  processes  of  Dittmar  and  Robinson,  and  of 
Dupre  and  Hake;  but  as  the  results  are  mainly  obtained  by  the 
balance,  and  not  by  volumetric  means,  the  reader  is  referred  to  the 
original  papers  contributed  to  the  Journal  of  the  Chemical  Society. 


PREPARATION    OF    THE    REAGENTS    FOR    THE    SANITARY 
ANALYSIS    OF    WATERS    WITHOUT    GAS    APPARATUS. 

§  91.  THE  Water  Committee  of  the  Society  of  Public  Analysts 
of  Great  Britain  and  Ireland  have  drawn  up  some  very  concise 
directions  for  the  practice  of  water  analysis  for  sanitary  purposes, 
based  upon  well-known  processes,  the  essential  parts  of  which 
are  given  below.  There  are  some  slight  modifications,  such  as  the 
use  of  the  decem  or  10-grain  measure  instead  of  the  grain,  etc. 
The  insertion  here  of  these  directions  in  full,  or  nearly  so,  necessarily 
repeats  some  processes  which  have  been  already  described  in  §§  87 
and  88,  but  it  avoids  cross-references  and  at  the  same  time  gives 
some  slight  practical  modifications  which,  to  some  operators, 
may  seem  desirable.  The  Committee  recommend  the  results  to  be 
recorded  in  grains  per  imperial  gallon ;  but  whatever  system  of 
weights  and  measures  the  individual  analyst  may  use,  a  slight 
calculation  will  enable  him  to  state  the  results  in  any  required  way. 

F  F  2 


436  VOLUMETRIC   ANALYSIS.  §    91. 

Reagents   for   the   Estimation   of    Chlorine. 

Standard  Solution  of  Silver  nitrate. — Dissolve  4 '7887  parts  of 
pure  recrystallized  silver  nitrate  in  distilled  water,  and  make  the 
solution  up  to  1000  parts.  The  solution  is  to  be  standardized 
against  the  standard  solution  of  sodic  chloride,  and  adjusted  if 
necessary.  1  c.c.  =  0'001  gm.  of  chlorine,  or  1  dm.  =  0'01  grn.  of 
chlorine. 

Standard  Solution  of  Sodic  chloride. — Dissolve  1*648  part  of 
pure  dry  sodic  chloride  in  distilled  water,  and  make  the  solution 
up  to  1000  parts.  1  c.c.  contains  O'OOl  gm.  chlorine,  or  1  dm.  = 
O'Ol  grn.  of  chlorine. 

Potassic  monochromate. — 50  parts  of  potassic  monochromate 
are  dissolved  in  1000  parts  of  distilled  water.  A  solution  of 
silver  nitrate  is  added,  until  a  permanent  red  precipitate  is 
produced,  which  is  allowed  to  settle.  This  removes  any  accidental 
chlorine  in  the  salt. 


Reagent   for  the   Estimation   of   Phosphoric   Acid. 

Molybdic  Solution. — One  part  pure  molybdic  acid  is  dissolved 
in  4  parts  of  ammonia,  sp.  gr.  0'960.  This  solution,  after  filtration, 
is  poured  with  constant  stirring  into  15  parts  of  nitric  acid  of  1'20 
sp.  gr.  It  should  be  kept  in  the  dark,  and  carefully  decanted 
from  any  precipitate  which  may  form. 


Reagents   for   the   Estimation   of   Nitrogen   in   Nitrates. 

Concentrated  Sulphuric  acid. — In  order  to  ensure  freedom  from 
oxides  of  nitrogen,  this  should  be  kept  in  a  bottle  containing 
mercury,  and  agitated  from  time  to  time,  which  will  ensure  their 
absence. 

Metallic  Aluminium. — As  thin  foil. 

Solution  of  Sodic  hydrate. — Dissolve  100  parts  of  solid  sodic 
hydrate  in  1000  parts  of  distilled  water.  When  cold,  introduce 
a  strip  of  about  100  square  c.m.,  say  fifteen  square  inches,  of 
aluminium  foil,  previously  heated  just  short  of  redness,  wrapped 
round  a  glass  rod.  When  the  aluminium  is  dissolved,  boil  the 
solution  briskly  in  a  porcelain  basin  until  about  one-third  of  its 
volume  has  been  evaporated,  allow  it  to  cool,  and  make  it  up  to  its 
original  volume  with  water  free  from  ammonia.  The  solution  must 
be  tested  by  a  blank  experiment  to  prove  the  absence  of  nitrates. 

Broken  Pumice. — Clean  pumice,  broken  into  pieces  of  the  size 
of  small  peas,  sifted  free  from  dust,  heated  to  redness,  and  kept 
in  a  closely  stoppered  bottle. 


§    91.  NATURAL  WATERS   AND   SEWAGE.  437 

Hydrochloric  acid  free  from  Ammonia. — If  the  ordinary  pure 
acid  is  not  free  from  ammonia,  it  should  be  distilled.  As  only  two 
or  three  drops  are  used  in  each  experiment,  it  will  be  sufficient 
if  that  quantity  does  not  contain  an  appreciable  proportion  of 
ammonia. 

Copper  sulphate  Solution. — Dissolve  30  parts  of  pure  copper 
sulphate  in  1000  parts  of  distilled  water. 

Metallic  Zinc. — As  thin  foil.  This  should  be  kept  in  a  dry 
atmosphere,  so  as  to  be  preserved  as  far  as  possible  from  oxidation. 

Standard  Solution  of  Ammonic  chloride  (see  below). 
Xessler's  Solution  (see  below). 


Reagents   for  the   Estimation   of   Nitrogen   as   Ammonia   and 
Albuminoid   Ammonia. 

Concentrated  Standard  Solution  of  Ammonic  chloride. — Dissolve 
3 '15  parts  of  pure  ammonic  chloride  in  1000  parts  of  distilled  water 
free  from  ammonia. 

Standard  Solution  of  Ammonic  chloride. — Dilute  the  above 
with  pure  distilled  water  to  100  times  its  bulk.  This  solution  is 
used  for  comparison  in  Nesslerizing,  and  contains  one  part  of 
ammonia  (!STH3)  in  100,000,  or  TJ^  m.gm.  in  each  c.c. 

Nessler  Solution. — Dissolve  35  parts  of  potassic  iodide  in 
100  parts  of  water.  Dissolve  17  parts  of  mercuric  chloride  in 
300  parts  of  water.  The  liquids  may  be  heated  to  aid  solution, 
but  if  so  must  be  cooled.  Add  the  latter  solution  to  the  former 
until  a  permanent  precipitate  is  produced.  Then  dilute  with 
a  20  per  cent,  solution  of  sodic  or  potassic  hydrate  to  1000  parts ; 
add  mercuric  chloride  solution  until  a  permanent  precipitate  again 
forms ;  allow  to  stand  till  settled,  and  decant  off  the  clear  solution. 
The  bulk  should  be  kept  in  an  accurately  stoppered  bottle,  and 
a  quantity  transferred  from  time  to  time  to  a  small  bottle  for  use. 
The  solution  improves  by  keeping.  It  will  be  noticed  that  this 
solution  is  only  about  half  the  strength  of  the  one  given  on  page 
374 ;  of  course  a  larger  volume  has  to  be  used  in  testing. 

Sodic  carbonate. — A  20  per  cent,  solution  of  recently  ignited 
pure  sodic  carbonate. 

Alkaline  Permanganate  Solution. — Dissolve  200  parts  of  potassic 
hydrate  and  eight  parts  of  pure  potassic  permanganate  in  1100  parts 
of  distilled  water,  and  boil  the  solution  rapidly  till  concentrated  to 
1000  parts. 

Distilled  Water  free  from  Ammonia  (see  page  375). 


438  VOLUMETRIC  ANALYSIS.  §    91. 

Reagents   for  the   Estimation   of    Oxygen   absorbed. 

Standard  Solution  of  Potassic  permanganate. — Dissolve  0'395 
part  of  pure  potassic  permanganate  in  1000  of  water.  Eacli  c.c. 
contains  O'OOOl  gm.  of  available  oxygen,  and  each  dm.  contains- 
O'OOl  grn. 

Potassic  iodide  Solution. — One  part  of  the  pure  salt  recrystallized 
from  alcohol,  dissolved  in  ten  parts  of  distilled  water. 

Dilute  Sulphuric  acid. — One  part  by  volume  of  pure  sulphuric 
acid  is  mixed  with  three  parts  by  volume  of  distilled  water,  and 
solution  of  potassic  permanganate  dropped  in  until  the  whole 
retains  a  very  faint  pink  tint,  after  warming  to  80°  F.  for  four 
hours. 

Sodic  thiosulphate. — One  part  of  the  pure  crystallized  salt 
dissolved  in  1000  parts  of  water. 

Starch  Indicator. — The  best  form  in  which  to  use  this  is  the 
alkaline  solution,  page  116. 


Reagents   for  the   Estimation   of   Hardness. 

Concentrated  Standard  Solution  of  Calcic  chloride. — Dissolve 
1-144  gm.  of  pure  crystallized  calc-spar  in  dilute  hydrochloric  acid 
(with  the  precautions  given  on  page  380),  then  dissolve  in  water, 
and  make  up  to  a  liter.  On  the  grain  system,  a  solution  of  the  same- 
strength  is  made  by  dissolving  11 '44  grn.  of  calc-spar  in  1000  dm. 

Standard  Water  of  8°  Hardness. — This  is  made  by  diluting  the 
foregoing  concentrated  solution  to  ten  times  its  volume  with 
freshly  boiled  and  cooled  distilled  water. 

Standard  Soap  Solution  (is  made  precisely  as  directed  on  page 
380). — It  should  be  of  such  strength  as  just  to  form  a  permanent 
lather,  when  18  c.c.  or  dm.  measures  are  shaken  with  100  c.c.  or 
dm.  of  water  of  8°  hardness.  The  following  table  will  then  give 
the  degrees  of  hardness  corresponding  to  the  number  of  c.c.  or  dm. 
measures  employed. 

c.c.  or  dm.  c.c.  or  din. 

Hardness.  Measures.  Hardness.  Measures. 

0°  0-9  5°  12-0 

1°  2-9  6°  14-0 

2°  5-4  7°  16-0 

3°  7-7  8°  18-0 

4°  9-9 

After  which  one  degree  =  2  c.c.  or  dm.  measures.  This  is  the 
last  solution  recommended  by  Dr.  Clark,  and  differs  slightly 


§    91.  NATURAL  WATERS   AND   SEWAGE.  4S9 

from  the  scale  given  on  page  414  ;  the  variation,  however,  is  very 
insignificant,  except  in  the  first  two  stages  of  the  table. 


The  Analytical  Processes. 
Collection  of  Samples. — The  same  as  directed  on  page  381. 

Appearance  in  Two-foot  Tube. — The  colour  or  tint  of  the  water  must 
be  ascertained,  by  examination,  in  a  tube  two  feet  long  and  two  inches  in 
diameter.  This  tube  should  be  made  of  glass  as  nearly  colourless  as  may  be, 
and  should  be  covered  at  each  end  with  a  disc  of  perfectly  colourless  glass, 
cemented  on,  an  opening  being  left  for  filling  and  emptying  the  tube.  This 
opening  may  be  made,  either  by  cutting  a  half-segment  off  the  glass  disc  at 
one  end,  or  by  cutting  a  small  segmental  section  out  of  the  tube  itself,  before 
the  disc  is  cemented  on.  These  tubes  are  most  conveniently  kept  on  hooks 
in  a  horizontal  position  to  prevent  the  entrance  of  dust. 

The  tube  must  be  about  half-filled  with  the  water  to  be  examined,  brought 
into  a  horizontal  position  level  with  the  eye,  and  directed  towards  a  well- 
illuminated  white  surface.  The  comparison  of  tint  has  to  be  made  between 
the  lower  half  of  the  tube  containing  the  water  under  examination,  and  the 
upper  half  containing  atmospheric  air  only. 

Smell. — Put  not  less  than  three  or  four  ounces  of  the  water  into  a  clean 
eight-ounce  wide-mouthed  stoppered  glass  bottle,  which  has  been  previously 
rinsed  with  the  same  water.  Insert  the  stopper,  and  warm  the  water  in  a 
water  bath  to  100°  P.  (38°  C.).  Eemove  the  bottle  from  the  water  bath,  rinse 
it  outside  with  good  water  perfectly  free  from  odour,  and  shake  it  rapidly 
for  a  few  seconds ;  remove  the  stopper,  and  immediately  observe  if  the  water 
has  any  smell.  Insert  the  stopper  again,  and  repeat  this  test. 

When  the  water  has  a  distinct  odour  of  any  known  or  recognised  polluting 
matter,  such  as  peat  or  sewage,  it  should  be  so  described ;  when  this  is  not 
the  case,  the  smell  must  be  reported  simply  as  none,  very  slight,  slight,  or 
marked,  as  the  case  may  be. 

Chlorine. — Titrate  at  least  100  c.c.  or  dm.  of  the  water  with  the  standard 
silver  nitrate  solution,  either  in  a  white  porcelain  basin  or  in  a  glass  vessel 
standing  on  a  porcelain  slab,  using  potassic  chromate  as  an  indicator.  The 
titration  is  conducted  as  follows : — The  sample  of  water  is  measured  into  the 
basin  or  beaker,  and  1  c.c.  or  1  dm.  of  potassic  chromate  solution  added. 
The  standard  silver  nitrate  solution  is  then  run  in  cautiously  from  a  burette, 
until  the  red  colour  of  the  precipitated  silver  chromate,  which  is  always 
observed  at  the  point  where  the  silver  solution  drops  in,  is  no  longer  entirely 
discharged  on  stirring.  The  burette  is  then  read  off.  It  is  best  to  repeat 
the  experiment,  as  follows :— Add  a  few  drops  of  dilute  sodic  chloride  solution 
to  the  water  last  titrated,  which  will  discharge  the  red  colour.  Measure  out 
a  fresh  portion  of  the  water  to  be  titrated  into  another  basin,  and  repeat  the 
titration,  keeping  the  first  sample,  the  colour  of  which  has  been  discharged, 
side  by  side  with  the  second,  so  as  to  observe  the  first  permanent  indication 
of  difference  of  colour.  If  the  quantity  of  chlorine  be  so  small  that  still 
greater  accuracy  is  necessary,  the  titration  may  be  conducted  in  the  same  way 
as  last  described,  but  instead  of  the  operator  looking  directly  at  the  water 
containing  the  chromate  solution,  he  may  place  between  the  basin  containing 
the  water  and  his  eye,  a  flat  glass  cell  containing  some  water  tinted  with  the 
chromate  solution  to  the  same  tint  as  the  water  which  is  being  tested,  or  may 
look  through  a  glass  coated  with  a  gelatine  film  coloured  with  the  same  salt 
(see  §  41).  Care  must  always  be  taken  that  the  water  is  as  nearly  neutral 
as  possible  before  titration.  If  originally  acid,  it  should  be  neutralized  with 


440  VOLUMETRIC   ANALYSIS.  §    91. 

precipitated  carbonate  of  lime.  If  the  proportion  of  chlorine  be  less  than 
0'5  grain  per  gallon,  it  is  desirable  to  take  a  larger  quantity  of  the  water,  say 
250  c.c.  or  350  dm.,  for  the  estimation,  and  to  concentrate  this  quantity  on 
the  water  bath  before  titrating  it,  so  as  to  bring  it  to  about  100  c.c.  or 
150  dm.  This  titration  may  be  performed  by  gas-light. 

Phosphoric  Acid. — The  ignited  total  residue,  obtained  as  hereafter 
directed,  is  to  be  treated  with  a  few  drops  of  nitric  acid,  and  the  silica 
rendered  insoluble  by  evaporation  to  dryness.  The  residue  is  then  taken 
up  with  a  few  drops  of  dilute  nitric  acid,  some  water  is  added,  and  the 
solution  is  filtered  through  a  filter  previously  washed  with  dilute  nitric 
acid.  The  filtrate,  which  should  measure  3  c.c.  (or  5  dm.),  is  mixed  with 
3  c.c.  of  molybdic  solution,  gently  warmed,  and  set  aside  for  fifteen  minutes, 
at  a  temperature  of  80°  F.  The  result  is  reported  as  "traces,"  "heavy 
traces,"  or  "very  heavy  traces,"  when  a  colour,  turbidity,  or  definite 
precipitate,  are  respectively  produced,  after  standing  for  fifteen  minutes. 
Another  method  is  given  on  page  416. 

Nitrogen  in  Nitrates. — This  may  be  determined  by  one  of  the  following 
processes :  viz.,  Crum,  Copper-zinc,  Aluminium,  or  Indigo.  Analysts  should 
report  which  process  is  employed. 

Crum  Process. — This  is  described  on  page  406,  or  it  may  be  carried  out  in 
a  Lunge's  nitrometer  as  follows: — 250  c.c.  or  dm.  of  the  \vater  must  be 
concentrated  in  a  basin  to  2  c.c.  or  3  dm.  measure.  A  Lunge's  nitrometer 
is  charged  with  mercury,  and  the  three-way  stop-cock  closed,  both  to  measuring 
tube  and  waste  pipe.  The  concentrated  filtrate  is  poured  into  the  cup  at  the 
top  of  the  measuring  tube,  and  the  vessel  which  contained  it  rinsed  with  1  c.c. 
of  water,  and  the  contents  added.  The  stop-cock  is  opened  to  the  measuring 
tube,  and,  by  lowering  the  pressure  tube,  the  liquid  is  drawn  out  of  the  cup 
into  the  tube.  The  basin  is  again  rinsed  with  5  c.c.  of  pure  strong  sulphuric 
acid,  and  this  is  also  transferred  to  the  cup  and  drawn  into  the  measuring 
tube.  The  stop-cock  is  once  more  closed,  and  12  c.c.  more  sulphuric  acid  put 
into  the  cup,  and  the  stop-cock  opened  to  the  measuring  tube  until  10  c.c.  of 
acid  have  passed  in.  The  excess  of  acid  is  discharged,  and  the  cup  and  waste 
pipe  rinsed  with  water.  Any  gas  which  has  collected  in  the  measuring  tube 
is  expelled  by  opening  the  stop-cock  and  raising  the  pressure  tube,  taking 
care  no  liquid  escapes.  The  stop-cock  is  closed,  the  measuring  tube  taken 
from  its  clamp  and  shaken  by  bringing  it  slowly  to  a  nearly  horizontal 
position,  and  then  suddenly  raising  it  to  a  vertical  one.  This  shaking  is 
continued  until  no  more  gas  is  given  off,  the  operation  being,  as  a  rule, 
complete  in  fifteen  minutes.  Now  prepare  a  mixture  of  one  part  of  water 
with  five  parts  of  sulphuric  acid,  and  let  it  stand  to  cool.  After  an  hour, 
pour  enough  of  this  mixture  into  the  pressure  tube  to  equal  the  length 
of  the  column  of  acidulated  water  in  the  working  tube,  bring  the  two  tubes 
side  by  side,  raise  or  lower  the  pressure  tube  until  the  mercury  is  of  the  same 
level  in  both  tubes,  and  read  off  the  volume  of  nitric  oxide  (for  calculation 
of  nitrogen  see  page  400).  This  volume,  expressed  in  c.c.'s  and  corrected  to 
normal  temperature  and  pressure,  gives,  when  multiplied  by  0'175,  the 
nitrogen  in  nitrates,  in  grains  per  gallon,  if  250  c.c.  of  the  water  have 
been  used. 

Copper-zinc  Process  (already  described  on  page  408) . 

Aluminium  Process. — This  is  carried  out  as  follows : — 50  c.c.  or  100  dm. 
of  the  water  are  introduced  into  a  retort,  and  50  c.c.  or  100  dm.  of  a  10  per 
cent,  solution  of  caustic  soda,  free  from  nitrates,  added.  If  necessary,  the 
contents  of  the  retort  should  be  distilled  until  the  sample  is  free  from 
ammonia.  The  retort  is  then  cooled,  and  a  piece  of  aluminium  foil 
introduced  into  it.  The  neck  of  the  retort  is  inclined  upwards,  and  its 


§  91. 


NATURAL  WATERS  AND   SEWAGE.  441 


mouth  closed  with  a  perforated  cork,  through  which  passes  the  narrow  end 
of  a  small  chloride  of  calcium  tube  filled  with  powdered  pumice  or  glass 
beads  wetted  with  very  dilute  hydrochloric  acid  free  from  ammonia.  This 
tube  is  connected  with  a  second  tube  containing  pumice  stone  moistened 
with  strong  sulphuric  acid,  which  serves  to  prevent  any  ammonia  from  the 
air  entering  the  apparatus,  which  is  allowed  to  stand  in  this  way  for  a  few 
hours  or  overnight.  The  contents  of  the  first  absorption  tube — that  next 
the  retort— are  washed  into  the  retort  with  a  little  distilled  water  free  from 
ammonia,  and  the  retort  adapted  to  a  condenser.  The  contents  of  the  retort 
are  distilled  to  about  half  their  original  volume.  The  distillate  is  collected, 
and  an  aliquot  part  Nesslerized ;  and,  if  necessary,  the  rest  of  the  distillate 
is  diluted,  and  an  aliquot  part  again  Nesslerized  as  hereafter  directed. 

Indigo  Process  (already  described  on  page  239) . 

Ammonia,  Free  and  Saline. — The  estimation  of  ammonia  present  in 
the  water  in  a  free  or  saline  form,  and  of  that  yielded  by  the  nitrogenous 
matter  present  in  the  water  (commonly  called  albuminoid  ammonia),  is  to  be 
made  on  the  same  portion  of  the  sample  to  be  analyzed. 

Take  not  less  than  500  c.c.  or  700  dm.  (one  deci-gallon)  of  the  water  for 
these  determinations,  and  distil  in  a  40-oz.  stoppered  retort,  which  is  large 
enough  to  prevent  the  probability  of  portions  of  the  water  being  spirted 
over  into  the  condenser.  The  neck  of  the  retort  should  be  small  enough  to 
pass  three  or  four  inches  into  the  internal  glass  tube  of  a  Liebi  g's  condenser. 
If  the  fit  between  the  retort  and  the  inside  tube  of  the  condenser  is  good,  the 
joint  may  be  made  by  WTapping  a  small  piece  of  washed  tinfoil  round  the 
retort  tube  so  as  to  pass  just  inside  the  mouth  of  the  condenser  tube.  Many 
analysts  prefer,  however,  to  work  with  a  retort  fitting  loosely  into  the 
condenser;  and,  in  such  cases,  the  joint  between  the  two  maybe  made  in  one 
of  the  two  following  ways : — (1)  Either  by  an  ordinary  india-rubber  ring — 
such  as  those  used  for  the  top  of  umbrellas— which  has  been  previously  soaked 
in  a  dilute  solution  of  soda  or  potash— being  stretched  over  the  retort  tube 
in  such  a  position,  that  when  the  retort  tube  is  inserted  in  the  condenser  it 
shall  fit  fairly  tightly  within  the  mouth  of  the  tube,  about  half-an-inch  from 
the  end  :  (2)  Preferably,  when  the  shape  of  the  large  end  of  the  condenser 
admits  of  it,  by  a  short  length,  say  not  more  than  two  inches,  of  large  size 
india-rubber  tubing,  which  has  been  previously  soaked  in  a  dilute  solution  of 
soda  or  potash,  being  stretched  outside  both  retort  tube  and  condenser  tube, 
so  as  to  couple  them  together,  so  that  the  tube  of  the  retort  still  projects 
some  inches  into  that  of  the  condenser.  It  is  very  desirable  to  have  a 
constant  stream  of  water  round  the  condenser,  whenever  it  can  be  obtained. 
Before  distillation,  a  portion  of  the  water  must  be  tested  with  cochineal,  in 
order  to  ascertain  if  it  shows  an  alkaline  reaction.  The  portion  so  tested 
must,  of  course,  be  rejected,  and  not  put  into  the  retort.  If  the  water  does 
not  show  an  alkaline  reaction,  a  sufficient  quantity  of  ignited  sodic  carbonate, 
to  render  the  water  distinctly  alkaline,  must  be  added.  The  distillation 
should  then  be  commenced,  and  not  less  than  100  c.c.  or  150  dm.  distilled 
over.  The  receiver  should  fit  closely,  but  not  air-tight,  on  the  condenser. 
The  distillation  should  be  conducted  as  rapidly  as  is  compatible  with  a 
certainty  that  no  spirting  takes  place.  After  100  c.c.  or  150  dm.  have  been 
distilled  over,  the  receiver  should  be  changed,  that  containing  the  distillate 
being  stoppered  to  preserve  it  from  access  of  ammoniacal  fumes.  100  c.c. 
measuring  flasks  make  convenient  receivers.  The  distillation  must  be  con- 
tinued until  50  c.c.,  or,  say  75  dm.  more,  are  distilled  over  ;  and  this  second 
portion  of  the  distillate  must  be  tested  with  Nessler's  reagent,  to 
ascertain  if  it  contains  any  ammonia.  If  it  does  not,  the  distillation  for 
free  or  saline  ammonia  may  be  discontinued,  and  this  last  distillate  rejected; 
but  if  it  does  contain  any,  the  distillation  must  be  continued  still  longer,  until 


442  VOLUMETRIC  ANALYSIS.  §    91. 

a  portion  of  50  c.c.,  or  75  dm.,  when  collected,  shows  no  colouration  with  the 
N  essler  test.  The  whole  of  the  distillates  must  be  Nesslerized  as  follows  : — 
The  standard  solution  of  ammonia  for  comparison  is  that  given  on  page  437. 
The  distillate  is  transferred  to  a  clean  N  essler  glass,  and  one-twentieth 
of  its  volume  of  Nessler  solution  added.  No  turhidity  must  ensue  on 
the  addition  of  the  N  essler  solution  to  the  water,  as  such  turbidity  would 
be  a  proof  that  the  distillate  was  contaminated  by  reason  of  spirting,  and 
must,  therefore,  be  rejected,  and  the  determination  repeated. 

After  thoroughly  mixing  the  water  and  Nessler  solution  in  the  glass,  an 
approximate  estimate  can  be  formed  of  the  amount  of  ammonia  present,  by 
the  amount  of  colouration  produced  in  the  solution.  It  will  now  be  necessary 
to  mix  one  or  more  standard  solutions  with  which  to  compare  the  tint  thus 
obtained.  These  solutions  must  be  made  by  mixing  the  standard  solution  of 
ammonic  chloride  with  distilled  water  absolutely  free  from  ammonia,  and 
subsequently  adding  some  of  the  same  Nessler  solution  as  was  previously 
added  to  the  distillate.  This  precaution  is  essential,  because  the  tint  given 
by  different  samples  of  Nessler  solution  varies.  The  colorimeter  may  be 
used,  if  preferred,  instead  of  Nessler  glasses. 

Albuminoid  Ammonia. — As  soon  as  the  distillation  of  the  free  ammonia 
has  been  started,  the  alkaline  solution  of  permanganate  should  be  measured 
out  into  a  flask,  ready  for  addition  to  the  water  under  examination,  for  the 
distillation  of  the  albuminoid  ammonia.  The  volume  of  the  alkaline 
permanganate  solution  to  be  taken  must  be  at  least  one-tenth  of  that  of  the 
water  which  is  being  distilled ;  and  should  not  exceed  that  proportion  unless 
the  water  is  of  very  bad  quality,  and  the  solution  must  be  made  in  accordance 
with  the  directions  contained  in  these  instructions.  This  solution  must  be 
diluted  with  four  times  its  own  volume  of  water,  and  must  be  placed  in 
a  flask  and  boiled  during  the  whole  time  that  the  distillation  of  the  sample 
for  free  ammonia  is  being  carried  on,  care  being  taken  that  the  concentration 
does  not  proceed  to  too  great  an  extent.  There  must  be  enough  of  this 
boiled  and  diluted  alkaline  permanganate  solution  to  make  up  the  residue  in 
the  retort  to  about  500  c.c.  or  700  dm.  When  the  distillation  of  the  sample 
of  water  for  free  and  saline  ammonia  is  completed,  the  alkaline  permanganate 
solution,  which  has  been  thus  diluted  and  boiled,  will  be  ready  for  use, 
and  the  distillation  for  albuminoid  ammonia  may  be  proceeded  with,  as 
follows : — 

To  the  residue  left  in  the  retort  from  which  the  free  ammonia  has- 
been  distilled,  add  the  alkaline  permanganate  solution  to  make  it  up  again 
to  a  volume  of  at  least  500  c.c.,  or  say  700  dm.,  and  the  lamp  being  replaced, 
the  distillation  must  be  continued,  and  successive  portions  of  the  distillate 
again  collected  in  precisely  the  same  way  as  during  the  process  of  distillation 
for  free  ammonia. 

After  200  c.c.  or  300  dm.,  say  two-fifths  of  the  volume  contained  in  the 
retort,  have  been  distilled  over,  the  receiver  should  be  changed  and  further 
portions  of  50  c.c.  or  75  dm.  collected  separately,  until  the  distillate  is 
practically  free  from,  ammonia.  The  distillate  must  then  be  mixed,  and 
Nesslerized  in  the  same  way  as  previously  directed  for  free  ammonia.  The 
result  so  obtained  must  be  calculated  to  ammonia  in  grams  per  liter  or  grains 
per  gallon,  and  returned  as  albuminoid  ammonia. 

Special  care  must  be  taken  that  the  atmosphere  of  the  room  in  which  these 
distillations  are  performed  is  kept  free  from  ammoniacal  vapours,  and  that 
the  receivers  fit  close,  but  not  air-tight,  to  the  end  of  the  Liebig's 
condenser.  It  is  also  specially  necessary  to  observe  that  the  colour  of  the 
distillate  deepens  gradually  after  the  addition  of  the  Nessler  reagent,  and 
that  it  is  not  possible  to  read  off  the  amount  of  colour  correctly  until  the 
Nesslerized  liquor  has  stood  for  at  least  three  minutes,  and  been  intimately 
mixed  with  the  Nessler  solution  (see  also  note  page  384). 


§    91.  NATURAL  WATERS  AND   SEWAGE.  443 

Special  care  must  be  taken  that  the  retort,  condensers,  receivers,  funnels, 
Nessler  glasses,  etc.,  used  are  all  rendered  perfectly  free  from  ammonia 
before  use.  Where  the  water  in  use  in  the  laboratory  is  good,  this  may  be 
used  to  thoroughly  rinse  the  apparatus  two  or  three  times,  draining  out  the 
adhering  water ;  otherwise  pure  distilled  water  must  be  used.  These 
ammonia  and  albuminoid  ammonia  determinations  should  be  made  as  soon  as 
possible  after  the  water  has  been  received  for  analysis. 

Oxygen  Absorbed. — Two  separate  determinations  have  to  be  made,  viz., 
the  amount  of  oxygen  absorbed  during  fifteen  minutes,  and  that  absorbed 
during  four  hours.  Both  are  to  be  made  at  a  temperature  of  80°  P.  (27°  C.). 
It  is  most  convenient  to  make  these  determinations  in  12-oz.  stoppered  flasks, 
which  have  been  rinsed  with  sulphuric  acid  and  then  with  water.  Put 
250  c.c.  or  dm.  into  each  flask,  which  must  be  stoppered  and  immersed  in 
a  water  bath  or  suitable  air  bath  until  the  temperature  rises  to  80°  P.  Now 
add  to  each  flask  10  c.c.  or  10  dm.  of  the  dilute  sulphuric  acid,  and  then 
10  c.c.  or  10  dm.  of  the  standard  permanganate  solution.  Fifteen  minutes 
after  the  addition  of  the  permanganate,  one  of  the  flasks  must  be  removed 
from  the  bath  and  two  or  three  drops  of  the  solution  of  potassic  iodide  added 
to  remove  the  pink  colour.  After  thorough  admixture,  run  from  a  burette 
the  standard  solution  of  thiosulphate,  until  the  yellow  colour  is  nearly 
destroyed,  then  add  a  few  drops  of  starch  water,  and  continue  the  addition 
of  the  thiosulphate  until  the  blue  colour  is  just  discharged.  If  the  titration 
has  been  properly  conducted,  the  addition  of  one  drop  of  permanganate  will 
restore  the  blue  colour.  At  the  end  of  four  hours  remove  the  other  flask, 
add  potassic  iodide,  and  titrate  with  thiosulphate,  as  just  described.  Should 
the  pink  colour  of  the  water  in  the  flask  diminish  rapidly  during  the  four 
hours,  further  measured  quantities  of  the  standard  solution  of  permanganate 
must  be  added  from  time  to  time  so  as  to  keep  it  markedly  pink. 

The  thiosulphate  solution  must  be  standardized,  not  only  at  first,  but 
(since  it  is  liable  to  change)  from  time  to  time  in  the  following  way  : — To 
250  c.c.  or  dm.  of  pure  redistilled  water  add  two  or  three  drops  of  the  solution 
of  potassic  iodide,  and  then  10  c.c.  or  dm.  of  the  standardized  solution  of 
permanganate.  Titrate  with  the  thiosulphate  solution  as  above  described. 
The  quantity  used  will  be  the  amount  of  thiosulphate  solution  corresponding 
to  10  c.c.  or  10  din.,  as  may  be,  of  the  standardized  permanganate,  and  the 
factor  so  found  must  be  used  in  calculating  the  results  of  the  thiosulphate 
titrations  to  show  the  amount  of  the  standard  permanganate  solution  used, 
and  thence  the  amount  of  oxygen  absorbed. 

Great  care  should  be  taken  that  absolutely  pure  and  fresh  distilled  water 
is  used  in  standardizing  the  solution,  which  should  also  be  kept  in  the  dark 
and  cool.  It  suffices  to  compare  the  solution,  if  kept  in  this  way,  once  in 
three  or  four  days. 

The  amount  of  thiosulphate  solution  thus  found  to  be  required  to  combine 
with  the  iodine  liberated  by  the  permanganate  left  undecomposed  in  the 
water  is  noted  down,  and  the  calculation  made  as  follows  : — Let  A = amount 
of  thiosulphate  used  in  distilled  water,  and  B  =  that  used  for  water  under 
examination.  Then  A  expresses  the  amount  of  permanganate  added  to  the  water 
under  examination,  and  B  the  amount  of  permanganate  in  excess  of  that  which 
the  organic  matter  in  the  water  has  destroyed.  Therefore  A — B  is  the  amount 
actually  consumed.  If  the  amount  of  available  oxygen  in  the  quantity  of 
permanganate  originally  added  be  a,  the  oxygen  required  to  oxidize  the 

organic  matter  in  the  water  operated  on  would  be^    ~~       .    But  a  (available 

A 

oxygen  in  the  10  c.c.  of  standard  permanganate  used)=0'001  gm.    Therefore 
A— Bx  0-001  ,        nfn  A— BxO'4 

=  oxygen    for    250    c.c.;    or,    -. =  parts    of    oxygen 

•A.  A. 

required   for  100,000  parts  of  water.    Or,  in   other  words,  the   difference 


444  VOLUMETRIC   ANALYSIS.  §    91. 

between  the  quantity  of  thiosulphate  used  in  the  blank  experiment  and 
that  used  in  the  titration  of  the  samples  of  water  multiplied  by  the  amount 
of  available  oxygen  contained  in  the  permanganate  added,  and  the  product 
divided  by  the  volume  of  thiosulphate  corresponding  to  the  latter,  is  equal  to 
the  amount  of  oxygen  absorbed  by  the  water. 

Hardness  before  and  after  Boiling-. — Place  100  c.c.  or  100  dm.  of  the 
water  in  an  accurately  stoppered  8-oz.  flask.  Run  in  the  soap  solution  from 
a  burette  in  small  quantities  at  a  time.  If  the  water  be  soft,  not  more  than 
i  c.c.  or  dm.  at  a  time ;  if  hard,  in  quantities  of  1  c.c.  at  first.  After  each 
addition,  shake  the  flask  vigorously  for  about  a  quarter  of  a  minute.  As 
soon  as  a  lather  is  produced,  lay  the  flask  on  its  side  after  each  addition,  and 
observe  if  the  lather  remains  permanent  for  five  minutes.  To  ascertain  this, 
at  the  end  of  five  minutes  roll  the  flask  half-way  round  ;  if  the  lather  breaks 
instead  of  covering  the  whole  surface  of  the  water,  it  is  not  permanent ;  if  it 
still  covers  the  whole  surface  it  is  permanent ;  now  read  the  burette. 

Repeat  the  experiment,  adding  gradually  the  quantity  of  soap  solution 
employed  in  the  first  experiment,  less  about  2  c.c.  or  2  dm. ;  shake  as  before, 
add  soap  solution  very  gradually  till  the  permanent  lather  is  formed :  read 
the  burette,  and  take  out  the  corresponding  hardness  from  the  table.  If 
magnesian  salts  are  present  in  the  water  the  character  of  the  lather  will  be 
very  much  modified,  and  a  kind  of  scum  (simulating  a  lather)  will  be  seen 
in  the  water  before  the  reaction  is  completed.  The  character  of  this  scum 
must  be  carefully  watched,  and  the  soap  test  added  more  carefully,  with  an 
increased  amount  of  shaking  between  each  addition.  "With  this  precaution 
it  will  be  comparatively  easy  to  distinguish  the  point  when  the  false  lather 
due  to  the  magnesian  salts  ceases,  and  the  true  persistent  lather  is  produced. 

If  the  water  is  of  more  than  16°  of  hardness,  mix  50  c.c.  or  dm.  of  the 
sample  with  an  equal  volume  of  recently  boiled  distilled  water  which  has 
been  cooled  in  a  closed  vessel,  and  make  the  determination  on  this  mixture 
of  the  sample  and  distilled  water.  In  this  case  it  will,  of  course,  be 
necessary  to  multiply  the  figures  obtained  from  the  table  by  2. 

To  determine  the  hardness  after  boiling,  boil  a  measured  quantity  of  the 
water  in  a  flask  briskly  for  half  an  hour,  adding  distilled  water  from  time  to 
time  to  make  up  for  loss  by  evaporation.  It  is  not  desirable  to  boil  the  water 
under  a  vertical  condenser,  as  the  dissolved  carbonic  acid  is  not  so  freely 
liberated.  At  the  end  of  half  an  hour,  allow  the  water  to  cool,  the  mouth 
of  the  flask  being  closed;  make  the  water  up  to  its  original  volume  with 
recently  boiled  distilled  water,  and,  if  possible,  decant  the  quantity  necessary 
for  testing.  If  this  cannot  be  done  quite  clear,  it  must  be  filtered.  Conduct 
the  test  in  the  same  manner  as  described  above. 

The  hardness  is  to  be  returned  in  each  case  to  the  nearest  half-degree. 

Total  Solid  Matters. — Evaporate  250  c.c.  or  ^th  of  a  gallon,  in  a 
weighed  platinum  dish  on  a  water  bath ;  dry  the  residue  at  220°  F. 
(104°  C.),  and  cool  under  a  desiccator.  Weigh  the  dish  containing  the 
residue  accurately,  and  note  its  colour  and  appearance,  and  especially 
whether  it  rapidly  increases  in  weight.  Return  to  the  water  bath  for 
half  an  hour  and  re-weigh  until  it  ceases  to  lose  weight,  then  gradually 
heat  it  to  redness,  and  note  the  changes  which  take  place  during  this 
ignition.  Especially  among  these  changes  should  be  observed  the  smell, 
scintillation,  change  of  colour,  separation  of  more  or  less  carbon,  and  partial 
fusion,  if  any.  The  ignited  residue  is  to  be  used  for  the  estimation  of 
phosphoric  acid,  as  before  directed. 

Microscopical  Examination  of  Deposit. — The  most  convenient  plan 
of  collecting  the  deposit  is  to  place  a  circular  microscopical  covering  glass  at 
the  bottom  of  a  large  conical  glass  holding  about  20  oz.  The  glass  should 


8    91.  NATURAL   WATERS   AND   SEWAGE.  445 

o 

have  no  spout,  and  should  be  ground  smooth  on  the  top.  After  shaking  up 
the  sample,  this  vessel  is  filled  with  the  water,  covered  with  a  plate  of  ground 
glass,  and  set  aside  to  settle.  After  settling,  the  supernatant  water  is  drawn 
off  ty  a  fine  syphon,  and  the  glass  bearing  the  deposit  lifted  out,  either  by 
means  of  a  platinum  wire  (which  should  have  been  previously  passed  under 
it),  or  in  some  other  convenient  way,  and  inverted  on  to  an  ordinary 
microscopical  slide  for  examination.  It  is  desirable  to  examine  the  deposit 
first  by  a  4-th  and  then  by  a  fth  objective.  The  examination  should  be  made 
as  soon  as  the  water  has  stood  overnight.  If  the  water  be  allowed  to  stand 
longer,  organisms  peculiar  to  stagnant  water  may  be  developed  and  mislead 
the  observer.  Particular  notice  should  be  taken  of  bacteria,  infusoria,  ciliata 
or  flagellata,  disintegrated  fibres  of  cotton,  or  linen,  or  epithelial  debris. 

It  is  particularly  desirable  to  report  clearly  on  this  microscopical 
examination ;  not  merely  giving  the  general  fact  that  organisms  were 
present,  but  stating  as  specifically  as  possible  the  names  or  classes  of  the 
organisms,  so  that  more  data  may  be  obtained  for  the  application  of  the 
examination  of  this  deposit  to  the  characters  of  potable  waters. 

It  is  also  desirable  to  examine  the  residue  left  on  a  glass  slide  by  the 
evaporation  of  a  single  drop  of  the  water.  This  residue  is  generally  most 
conveniently  examined  without  a  covering  glass.  The  special  appearances  to 
be  noticed  are  the  presence  or  absence  of  particles  of  organic  matter,  or 
organized  structure,  contained  in  the  crystallized  forms  which  may  be  seen ; 
and  also  whether  any  part  of  the  residue  left,  especially  at  the  edges,  is 
tinted  more  or  less  with  green,  brown,  or  yellow. 

In  connection  with  the  microscopical  examination  it  may  be  desirable  to 
adopt  Heisch's  sugar  process  as  follows  : — 

Sugar  Test. — The  name  of  this  process  relates  simply  to  the  reagent 
which  is  used ;  namely,  pure  crystallized  sugar.  It  is  believed  to  be  a  test 
for  the  presence  of  the  germs  or  spores  of  the  sewage  fungus.  This  special 
form  of  fungus  grows  very  rapidly  in  water  containing  even  a  small  admixture 
of  sewage  water,  especially  if  sugar  be  present.  It  grows  as  well  in  a  closed 
bottle  of  the  liquid  being  tested,  as  in  water  exposed  to  the  air,  and  even 
better  in  an  atmosphere  of  carbonic  acid. 

To  apply  the  test: — Take  a  5-oz.  stoppered  flask  which  has  been  thoroughly 
cleaned  and  rinsed  with  the  water  to  be  tested.  Pill  with  the  water  to  be 
examined,  add  about  10  grn.,  or  say,  0'5  gm.  of  crystals  of  pure  sugar,  insert 
the  stopper,  and  put  the  flask  in  a  good  light;  keep  it  at  a  temperature 
of  as  nearly  as  possible  of  80°  P.  (27°  C.).  The  water  should  be  free  from 
suspended  matters  before  the  experiment  is  made. 

The  flask  must  be  carefully  examined  after  two  or  three  hours,  and  again 
if  necessary  at  intervals.  The  fungus  appears  first  in  the  form  of  minute 
floating  white  specks,  which  are  generally  easily  visible  to  the  naked  eye  in  a 
good  side-light  when  the  flask  is  looked  at  against  a  black  background.  A 
pocket  lens  may  sometimes  be  used  with  advantage. 

If  any  suspected  speck  is  seen  it  must  be  caught  by  a  fine  pipette  and 
transferred  to  a  glass  slide,  covered,  and  examined  with  a  ^th  objective. 

When  first  seen,  these  specks  are  found  to  consist  of  small  isolated  cells 
with  a  bright  nucleus.  In  the  second  stage  the  form  resembles  a  bunch  of 
grapes.  The  bright  nucleus  is  still  seen.  This  second  stage  generally 
takes  not  more  than  four  to  six  hours  for  full  development.  A  few  hours 
after  the  second  stage  has  become  clear,  the  cells  assume  the  form  of 
moniliform  threads.  After  this  they  assume  the  form  of  ordinary  mycelium, 
with  sparsely  diffused  cells.  Finally  the  cells  disappear  and  leave  only 
ordinary  mycelium. 

When  the  proportion  of  sewage  is  large,  it  is  often  accompanied  by  a 
distinct  smell  of  butyric  acid. 

A  few  experiments  on  mixtures  of  small  proportions  of  sewage  matter 


446  VOLUMETKIC  ANALYSIS.  §    92. 

with  water  will  give  sufficient  data  to  enable  this  peculiar  fungus  to  be 
readily  recognized. 

Reporting  tlie  Results  of  "Water  Analysis.— The  Report  of  the 
Committee  appointed  by  the  British  Association  to  confer  with  the  Committee 
of  the  American  Association  with  a  view  of  forming  a  uniform  system  of 
recording  results  of  Water  Analysis,  B.  A.  Meeting,  1889  (Chem.  Neivs, 
60,  203 — 204)  is  as  follows :— The  committee  recommend  a  system  of 
statement  for  a  complete  analysis  of  which  the  following  is  an  epitome. 
Results  to  be  expressed  in  parts  per  100,000.  In  a  potable  water,  the  numbers 
to  be  given  in  the  following  order:  Total  solid  matters  (a)  in  suspension, 
(5)  in  solution ;  organic  carbon ;  organic  nitrogen ;  oxygen  consumed,  as 
indicated  by  decoloration  of  permanganate;  ammonia  expelled  on  boiling 
with  sodic  carbonate;  ammonia  expelled  on  boiling  with  alkaline  perman- 
ganate ;  nitrogen  as  nitrates  and  nitrites ;  chlorine ;  hardness — temporary, 
permanent,  total.  In  a  mineral  water — carbonate  of  lime;  carbonate  of 
magnesia;  carbonate  of  soda  (calculated  from  residual  alkalinity  after 
boiling  and  filtering  off  precipitated  CaCO3  and  MgCO3) ;  total  of  each 
of  the  following  elements— calcium,  magnesium,  potassium,  sodium,  iron 
(ferrous),  iron  (ferric),  and  each  of  the  following  radicles — sulphuric  (SO4), 
nitric  (NO3),  nitrous  (NO2),  phosphoric  (PO4),  silicic  (SiO3) ;  then  each  of 
the  elements — chlorine,  bromine,  and  iodine,  and  of  sulphur  as  sulphide. 
Dissolved  gases :  c.c.  at  0°  C.  and  760  nun.  in  1  liter  of  water.  Carbonic 
anhydride  (CO2)  ;  oxygen ;  nitrogen ;  sulphuretted  hydrogen. 

They  consider  that  this  uniform  method  should  be  adopted  in  all  cases 
where  communications  come  before  learned  bodies  and  whenever  possible  in 
professional  practice ;  that  the  decimal  numerical  notation  is  to  be  preferred ; 
that  the  different  scales  for  potable  and  mineral  waters  suggested  by  the 
American  Committee  are  undesirable ;  that  all  results  obtained  by  calculation 
should  be  sharply  distinguished  from  those  obtained  by  direct  determination ; 
that  a  statement  of  mineral  constituents  combined  as  salts  is  not  to  be 
approved  of  unless  the  analytical  data  upon  which  it  is  based  are  clearly 
stated ;  that  the  American  Committee's  suggestion  of  recording  the  proportion 
of  each  element  of  binary  compounds,  and  recording  all  the  oxygen  in 
oxy-compounds  in  combination  with  the  negative  element,  as  indicated 
above,  is  the  most  convenient  for  all  purposes  of  calculation,  although  the 
want  of  a  name  for  these  negative  groups  and  the  custom  of  quoting 
metallic  elements  as  bases  are  objections  to  this  system;  finally,  that  volumes 
of  dissolved  gases  may  be  given  as  above,  or  in  volumes  of  gas  per  100 
volumes  of  water. 


OXYGEN    DISSOLVED    IN    WATERS. 

§  92.  THE  necessary  apparatus  and  standard  solutions  for 
carrying  out  this  estimation  are  described  in  §  68  (page  254), 
together  with  the  methods  of  manipulation. 

The  interpretation  of  the  results  as  regards  polluted  waters,  as 
given  by  Dupre,  may  be  summarized  as  follows  : — 

The  method  depends  on  the  fact  that,  if  a  perfectly  pure  water  is 
once  fully  aerated,  and  then  kept  in  a  bottle  so  that  it  could  neither 
lose  nor  gain  oxygen,  it  would  remain  fully  aerated  for  any  length 
of  time ;  but,  on  the  other  hand,  if  the  water  contained  living 
organic  matters  capable  of  absorbing  oxygen,  such  water  would  after 
a  period  of  time  contain  less  oxygen,  the  loss  so  found  being  taken 
as  the  measure  of  impurity.  The  method  is  really  another  form  of 


§    92.  NATURAL  WATERS   AND   SEWAGE.  447 

ascertaining  the  presence  of  germs  and  their  amount  in  contrast  to 
the  method  of  cultivation  by  gelatine  and  microscopic  analysis. 

The  practical  results  from  various  experiments  made  by  Dupre, 
and  reported  by  him  to  the  Medical  Department  of  the  Local 
Government  Board,  1884,  are  as  follows  : — 

(1)  A  water  which  does  not  diminish  in  its  degree  of  aeration  during 
a  given  period  of  time,  may  or  may  not  contain  organic  matter,  but 
presumably  does  not  contain  growing  organisms.     Such  organic  matter 
therefore  as  it  may  be  found  to  contain  by  chemical  analysis  (permanganate 
or  otherwise)  need  not  be  considered  as  dangerous  impurity. 

(2)  A  water  which  by  itself,  or  after  the  addition  of  gelatine  or  other 
appropriate  cultivating  matter,  consumes  oxygen  from  the  dissolved  air  at 
lower  temperatures,  but  does  not  consume  any  after  heating  for  say  three 
hours  at  60°  C.,  may  be  regarded  as  having  contained  living  organisms,  but 
none  of  a  kind  able  to  survive  exposure  to  that  temperature. 

(3)  A  water  which  by  itself,  or  after  addition  of  gelatine  or  the  like, 
continues  to  absorb  oxygen  from  its  contained  air  after  heating  to  60°  C.,  may 
be  taken  as  containing  spores  or  germs  able  to  survive  that  temperature. 

The  exact  nature  of  organisms  differing  in  this  way  is  of  course 
not  revealed  by  the  method.  D  up  re's  conclusion  is,  that  in  the 
vast  majority  of  cases  the  consumption  of  oxygen  from  the  dissolved 
air  of  a  natural  water  is  due  to  growing  organisms,  and  that  in  the 
complete  absence  of  such  organisms  little  or  no  oxygen  would  be 
then  consumed. 

The  paper  is  accompanied  by  tables  of  results  of  analysis  by  this 
and  other  methods,  which  are  too  voluminous  to  insert  here. 

Principle  of  the  method. — Dupre  states  that  a  water,  fully  aerated, 
contains  at  20°  C.  and  760  m.m.  pressure  0'594  grain  of  oxygen  per  gallon, 
or  0'04158  gm.  per  liter.*  The  proportion  varies  with  the  temperature  and 
pressure.  The  formula  given  by  Bun  sen  is  adopted  in  this  method— 

a=  2-0225  j8;  and  j8=0'020346  -  0-00052887£+0;000011156£2; 
where  a  is  the  co-efficient  of  absorption  of  oxygen  in  cubic  centimeters, 
£  the  co-efficient  for  absorption  of  nitrogen,  and  t  the  temperature. 

The  variation  due  to  atmospheric  pressure  is  so  slight  that  it 
may  practically  be  disregarded.  The  composition  of  air  is  taken  as 
2 1  volumes  oxygen  and  7  9  nitrogen.  Dupre  adopts  the  temperature 
of  20°  C.  for  all  waters  under  experiment;  and  as  a  rule  the 
samples  were  all  placed  in  an  appropriate  bottle,  and  kept  at 
a  constant  temperature  of  20°  C.  for  ten  days  previous  to  the 
estimation  of  the  oxygen. 

The  maximum  degree  of  oxygen  which  a  pure  water  should 
contain  at  this  temperature  is  called  100,  and  any  less  degree  found 
on  analysis  is  recorded  as  a  percentage  of  this  maximum. 

The  Analysis :  The  sample  of  water  is  placed  in  an  ordinary  bottle,  and 
vigorously  shaken  to  ensure  full  aeration ;  after  standing  the  requisite  time 
it  is  poured  into  the  experimental  bottle,  and  the  estimation  of  oxygen 
carried  out  as  described  in  §  68. 

*  Eoscoe  and  Lunt,  and  also  Dittmar,  show  by  their  experiments  that  these 
figures  are  too  low. 


448 


VOLUMETRIC   ANALYSIS. 


92. 


Calculation   of   the   Results   of   Water  Analysis. 


Substance  estimated. 

Measure  of  water 
taken. 

Volume  or  weight 
obtained  or  used. 

Factor  for  grains  per 
gallon. 

Cl           .'        .'        . 

100  c.c.  or  dm.  . 

(  c.c.  or  dm.  stan-  ) 
(  dard  AgNO3        j 

x        0-7      -Cl 

•         • 

140dm.(?Vgal.)' 

dm.     „       „      „ 

x          0-5        =  Cl 

N  as  HNO3          ( 
(Crum)            1 

250  c.c.     . 
250  dm.     . 

SSOdm.^gal.) 

c.c.  of  NO 

33                    55 
55                  5» 

x        0-175  =N 
x         0-27     -N 
x         0-193  =N 

/• 

100  c.c.     . 

grams  of  NH3 

x     576*45     =N 

NH3  copper-zinc   j 

50  c.c.      . 

yy             yy 

x  1152-9       =N 

or  aluminium  1 

150  dm.     . 

grains  of  NH3 

x       38-43     =N 

P 

100  dm.     . 

x       57-64     =N 

Free  or  Alb.  NH3 

500  c.c.     . 

(  c.c.  standard         ") 
>      NH4C1             3 

x         00014=NH:i 

55                  55                  35 

700  dm.     . 

dm.    „      „      „ 

x         00-1     =NH3 

O  absorbed    . 

250  c.c.     . 

(  10,  15,  or  20  c.c.  } 
J.     permanganate  3 

C  x  0'28(lorl'5or 
(      2—  J  )  ~ 

55                  55                  55 

350dm.    .        . 

C  10,  15,  or  20  dm.  ") 
^     permanganate  3 

C  x  0'02(lorl.5or 
|      2-?*)  =0 

Total  solids   .     '  „ 

250  c.c.     . 

grams 

x     280-0 

55                  33 

350  dm.     . 

grains 

x       20-0 

Coefficients  and  Logarithms   for  Volumetric  Analysis. 


Normal  H2S04 

Normal  HC1 
Normal  HNO3 

Normal  H2C2O4 
Normal  Acid 


Coefficients. 
1  c.c.=0'049         gm. 

„     =0-048 

„     =0-040 
1  c.c.=0-0365 

„     =0-0355 
1  c.c.=0'063 

„     =0-062 

„     =0-054 
1  c.c.=0'063 

„     =0-045 
1  c.c.=0'017 

„     =0-035 

„     =0-191 

„     =0-037 

„     =0-028 

„     =0-05 

„     =0-0855 

„    =0-1575 

„     =0-0985 

„     =0-02 

„     =0-042 

„     =0-056 

„     =0-069 
,     =0-188 


H2S04 

SO4 

SO3 

HC1 

Cl      

HNO3 

NO3 

N2O5 

H2C-O4,  20H2 

H2C204 

NH3 

NH4HO      ... 

Na2B2O'10H2O 

Ca2HO 

CaO 

CaCO3 

BaH2O2 

BaH2028H20 

BaCO3 

MgO 

MgCO3 

KHO 

K2C03 

KHC4H4OG... 


Logarithms. 
2-6901961 
2-6812412 
2-6020600 
2-5622929 
2-5502284 
2-7993405 
2-7923917 
2-7323938 
2-7993405 
2-6532125 
2-2304489 
2-5440680 
1-2810334 
2-5682017 
2-4471580 
2-6989700 
2-9319661 
1-1972806 
2-9934362 
2-3010300 
2-6232493 
2-7481880 
2-8388491 
1-2741578 


*  A=c.c.  or  dm.  of  thiosulphate  solution  corresponding  to  10  c.c.  or  dm.  of  perman- 
ganate. B=c.c.  or  dm.  of  thiosulphate  solution  used  after  the  time  of  reaction  is 
complete. 


92. 


COEFFICIENTS   AND   LOGARITHMS. 


449 


Coefficients. 
Normal  Acid  1  c.c.=0'102        gm. 

„     =0-098  ,    KC2H302     ... 

„    =0-141  ,    KNaC4H4O° 

„     =0-04  ,    NaHO 

„     =0-053  ,    Na2CO3 

„    =0-143  ,    Na2CO310H2O 

„    =0-084          •  ,    NaHCO3      ... 
Normal  NaHO  1  c.c.=0*040  ,    NaHO 

„    =0-031  ,    Na2O 

Normal  KHO  1  c.c.=0*056  ,    KHO 

„    =0-047  ,    K2O 

Normal  Na2CO3          1  c.c.=0*053  ,    Na2CO3 

„    =0*030  ,    CO3  ... 

„    =0*022  ,    CO2 ; 

Normal  Alkali  1  c.c.=0'06  ,    HC2H3O2     ... 

„     =0-07  ,    H3C6H5O'H-O 

„     =0-0365  ,    HC1 

=0-0808  ,    HB2... 

=0-0128  ,    HI 

=0*063  ,    HNO3 

=0-049  ,    H2SO4 

=0-075 

/u-  Silver  1  c.c.=0'0108 

„     =0-017 
„     =0-00355 
„     =0-00535 
„     =0-00745 
„     =0-0119 
„     =0-0103 
„     =0-0064 

^  Iodine  1  c.c.=0'0032 

„     =0-0041 
„     =0-00495 
„     =0-0248 
„     =0-0126 
„     =0-0097 

£r  Bichromate  1  c.c.=0'0456 

„     =0-051 
„     =0-0849 
3j     =0-0348 
5j     =0-0696 
„     =0-0216 

T^  Thiosulphate          1  c.c.=0'0248 
„     =0-0127 
„     =0-00355 
„     =0-0080 
CALCIUM  (Ca=40) 

1  c.c.  ^r  permanganate=0*0028  gm.  CaO          

=0-0050  gm.  CaCO3      

=0-0086  gm.  CaSO4,  2OH2      ... 
„          normal  oxalic  acid=0'0280  gm.  CaO   ...         ...• 

Cryst.  oxalic  acid  x  0*444    =CaO 

Double  iron  salt   xO*07143=CaO  .i..-.\v,..         ... 

CHLORINE  (01=35-37) 

1  c.c.  T-V  silver  solution=0*003537  gm.  Cl         

=0*005837  gm.  NaCl 

„         arseuious  or  thiosulphate  solution=0*003537  gm.  01. 


Ag 

AgNO3        ... 

Cl      

NH4C1 

KC1 

KBr 

NaBr 
Na2HAs04  ... 

SO2 

H2S03 

As203 

Na2S2O35H2O 

Na2SO37H2O 

K2S032H20 

PeSO4 

Ee2S04H20... 

FeS047H2O... 

PeCO3 

Fe304 

PeO 

Sodic  thiosulphate 

Cl 
Br 


Logarithms. 

1-0086002 

2-9912261 

1*1492191 

2-6020600 

2-7242759 

1*1553660 

2*9242793 

2-6020600 

2*4913617 

2-7481880 

2*6720979 

2*7242759 

2*4771213 

2-3424227 

2*7781513 

2*8450980 

2*5622929 

2*9074114 

1*1072100 

2*7993405 

2*6901961 

2*8750613 

2-0334238 

2-2304489 

3-5502284 

3-7283538 

3-8721563 

2-0755470 

2-0128372 

3*8061800 

3-5051500 

3-6127839 

3-6946052 

,  2-3944517 

2-1003705 

,  3-9867717 

2-6589648 

,  2-7075702 

2*9289077 

,  2-5415792 

,  2-8426092 

,  2-3344538 

.  2-3944517 

,  2-1038037 

3*5502284 

,  3-9030900 

.  3-4471580 
.  3-6989700 
.  3-9344985 
.  2-4471580 
.  1-6473830 
2-8538807 


3-5486351 
3-7661897 
3-5486351 


G  G 


450 


VOLUMETRIC  ANALYSIS. 


92. 


CHROMIUM  (Cr=52'4) 
Metallic  iron  x  0'3123=Cr 
„  xO'5981=CrO3 

xO'8784=K2Cr2(y... 

x  1-926  =PbCrO4  ... 

Double  iron  salt  x  0'0446=Cr      ... 

xO'0854=Cr03  ... 

x  01255=K2Cr2O7 

x  0-275  =PbCrO4 

1  c.c.  ^j-  solution=0'003349  gm.  CrO3    . 
„  „       =0-00492  gm.  K2Cr20' 

COPPEE  (Cu=63) 

1  c.c.  yV  solution=0'0063  gm.  Cu       •    . 

Iron  x  1' 1 25=copper 

Double  iron  salt  x  0'1607=copper 

CYANOGEN  (CN=26) 

1  c.c.  ^  silver  solution=0'0052 
=0-0054 
=0-01302 


gm.  CN 
gm.  HCN 
gm.  KCN 


",    &  iodine  =0'003255  gm.  KCN 

POTASSIC  FEREOCYANIDE  (K4FeCy6,  3OH2=422) 

Metallic  iron      x  7'541=cryst.  potassic  ferrocyanide 

Double  iron  salt  x  1-077=    „  „  „ 

POTASSIC  FEERICYANIDE  (K6Fe2Cy12=658) 
Metallic  iron       x  5*88    =potassic  f erricyanide 

Double  iron  salt  x  T68    =      „  „  

•&  thiosulphate  x  0*0329=      „  „  

GOLD  (Au=196*5) 

1  c.c.  normal  oxalic  acid=0'0655  gm.  gold        

IODINE  (1=126-6) 

1  c.c.  fV  thiosulphate=0'01265  gm.  iodine        

IEON  (Fe=56) 

1  c.c.  rV  permanganate,  bichromate^  or  thiosulphate 

=0-0056  Fe 
=0-0072  FeO 
„        =0-0080  Fe203 

LEAD  (Pb=206'4) 

1  c.c.  ^nr  permanganate  =0*01032  gm.  lead 

1  c.c.  normal  oxalic  acid=0'1032  gm.  lead 

Metallic  iron       xl'842=lead 

Double  iron  salt  x  0'263=lead 

MANGANESE  (Mn=55) 

MnO=7l.    MnO2=87. 

Metallic  iron  x  0-491    =Mn        

„  xO'fi3393=MnO 

xO-7768  =MnO2 

Double  iron  salt  xO'0911=MnO 

x  0-111  =MnO2 

Cryst.  oxalic  acid  x  0'6916=MnO2          

1  c.c.  ^  solution=0'00355  gm.  MnO     

=0-00435  gm.  MnO2 


Logarithms. 
1-4945720 
1-7767738 
1-9436923 
0-2846563 
2-6493349 
2-9314579 
1-0986437 
1-4393327 
3-5249151 
3-6919651 


3-7993405 
0-0511525 
1-2060159 


3-7160033 
37323938 
2-1146110 
3-5125510 


0-8774289 
0-0322157 


0-7693773 
0-2253093 
2-5171959 

2-8162413 
2-1020905 


3-7481880 
3-8573325 
3-9030900 


2-0136797 
1-0136797 
0-2652896 
1-4199557 


1-6910815 
1-8020413 
1-8903092 
2-9595184 
1-0453230 
1-8398550 
3-5502284 
3-6384893 


§    92.                      COEFFICIENTS  AND   LOGARITHMS.  451 

MEECUEY  (Hg=200)  Logarithms. 

Double  iron  salt  x  0'  5l04=Hg 17079107 

x  0-6914=HgCl2           T8397294 

1  c.c.  ^  solution=0'0200  gm.  Hg          2'3010300 

=0-0208  gm.  Hg2O      2-3180633 

=0-0271  gm.  HgCl2     2'4329693 

NlTBOGEN  AS  NlTEATES  AND  NlTBITES  (N2O5=108.      N2O3=76) 

Normal  acid  x  0'0540=N2O5  2'7323938 

xO-1011=KNO3 1-0047512 

Metallic  iron  x  0-3750=HNO3 1-5740313 

xO'6018=KNO3 1-7794522 

xO'3214=N2O5  1-5070459 

SILVEE  (Ag=107'66) 

1  c.c.  T»V  NaCl=0'010766  gm.  Ag           2-0320544 

=0-016966  gm.  AgNO3 2'2295795 

StTLPHUEETTED  HYDEOGEN  (H2S=34) 

1  c.c.  £f  arsenious  solution=0'00255  gm.  H2S 3'4065402 

TIN  (Sn=118) 

Metallic  iron  x  r0536=tin          ' 0'0226758 

Double  iron  salt  xO-1505=tin      1-1775365 

Factor  for  ^5-  iodine  or  permanganate  solution  0"0059...         ...  3*7708520 

ZINC  (Zn=65) 

Metallic  iron  x  0'5809=Zn           1-7641014 

x  0724  =ZnO         1-8597386 

Double  iron  salt  x  0-08298=Zu 2*9189734 

x  01034  =ZnO...                     T0145205 

1  c.c.  ^  solution=0-00325  gm.  Zn         3-5118834 


G  G  2 


452  VOLUMETRIC   ANALYSIS. 


PART  VII. 
VOLUMETRIC  ANALYSIS  OF  GASES. 

Description   of   the   necessary   Apparatus,    with.   Instructions   for 
Preparing1,    Etching",    Graduating',    etc. 

§  93.  THIS  branch  of  chemical  analysis,  on  account  of  its 
extreme  accuracy,  and  in  consequence  of  the  possibility  of  its 
application  to  the  analysis  of  carbonates,  and  of  many  other  bodies- 
from  which  gases  may  be  obtained,  deserves  more  attention  than 
it  has  generally  received,  in  this  country  at  least.  It  will  therefore 
be  advisable  to  devote  some  considerable  space  to  the  consideration 
of  the  subject. 

For  an  historical  sketch  of  the  progress  of  gas  analysis,  the 
reader  is  referred  to  Dr.  Frank  land's  article  in  the 
Handicorterbucli  der  Chemie,  and  more  complete  details 
of  the  process  than  it  will  be  necessary  to  give  here  will 
be  found  in  that  article;  also  in  Bun  sen's  Gasovietry, 
and  in  Dr.  Russell's  contributions  to  Watt's  Chemical 
Dictionary. 

The  apparatus  employed  by  Buns  en,  who  was  the  first 
successfully  to  work  out  the  processes  of  gas  analysis,  is 
very  simple,  Two  tubes,  the  absorption  tube  and  the 
eudiometer,  are  used,  in  which  the  measurement  and 
analysis  of  the  gases  are  performed.  The  first  of  these 
tubes  is  about  250  m.m.  long  arid  20  m.m.  in  diameter, 
closed  at  one  end,  and  with  a  lip  at  one  side  of  the  open 
extremity,  to  facilitate  the  transference  of  the  gas  from  the 
absorption  tube  (fig.  55)  to  the  eudiometer  (fig.  56).  The 
eudiometer  has  a  length  of  from  500  to  800  m.m.,  and 
a  diameter  of  20  m.m.  Into  the  closed  end  two  platinum 
wires  are  sealed,  so  as  to  enable  the  operator  to  pass  an 
electric  spark  through  any  gas  which  the  tube  may  contain. 
The  mode  of  sealing  in  the  platinum  wires  is  as  follows : — 
When  the  end  of  the  tube  is  closed,  and  while  still  hot, 
Pig.  55.  a  finely  pointed  blowpipe  flame  is  directed  against  the 
side  of  the  tube  at  the  base  of  the  hemispherical  end. 
When  the  glass  is  soft,  a  piece  of  white-hot  platinum  wire  is 
pressed  against  it  and  rapidly  drawn  away.  By  this  means  a 
small  conical  tube  is  produced.  This  operation  is  then  repeated 
on  the  opposite  side  (fig.  57).  One  of  the  conical  tubes  is  next 
cut  off  near  to  the  eudiometer,  so  as  to  leave  a  small  orifice  (fig.  58), 


§    93.  APPARATUS   FOR   ANALYSIS   OF   GASES.  453 

through  which  a  piece  of  the  moderately  thin  platinum  wire,  reaching 
about  two-thirds  across  the  tube,  is  passed.  The  fine  blow-pipe 
flame  is  now  brought  to  play  on  the  wire  at  the  point  where  it  enters 
the  tube;  the  glass  rapidly  fuses  round  the  wire,  making  a  perfectly 
gas-tight  joint.  If  it  should  be  observed  that  the  tube 
has  any  tendency  to  collapse  during  the  heating,  it  will 
be  necessary  to  blow  gently  into  the  open  end  of  the  tube. 
This  may  be  conveniently  done  by  means  of  a  long  piece 
of  caoutchouc  connector,  attached  to  the  eudiometer, 
which  enables  the  operator  to  watch  the  effect  of  the 
blowing  more  easily  than  if  the  mouth  were  applied 
directly  to  the  tube.  When  a  perfect  fusion  of  the  glass 
round  the  wire  has  been  effected,  the  point  on  the  opposite 
side  is  cut  off,  and  a  second  wire  sealed  in  in  the  same 
manner  (fig.  59).  The  end  of  the  tube  must  be  allowed 
to  cool  very  slowly;  if  proper  attention  is  not  paid  to 
this,  fracture  is  very  liable  to  ensue.  When  perfectly 
cold,  a  piece  of  wood  with  a  rounded  end  is  passed 
up  the  eudiometer,  and  the  two  wires  carefully  pressed 
against  the  end  of  the  tube,  so  as  to  lie  in  contact  with 
the  glass,  with  a  space  of  1  or  2  m.m.  between  their 
points  (fig.  60).  It  is  for  this  purpose  that  the  wires, 
Avhen  sealed  in,  are  made  to  reach  so  far  across  the  tube. 
The  ends  of  the  wires  projecting  outside  the  tube  are 
then  bent  into  loops.  These  loops  must  be  carefully 
treated,  for  if  frequently  bent  they  are  very  apt  to  break 
off  close  to  the  glass ;  besides  this,  the  bending  of  the 
wire  sometimes  causes  a  minute  crack  in  the  glass,  which 
may  spread  and  endanger  the  safety  of  the  tube.  These 
difficulties  may  be  overcome  by  cutting  off  the  wire  close 
to  the  glass,  and  carefully  smoothing  the  ends  by  rubbing 
them  with  a  piece  of  ground  glass  until  they  are  level 
with  the  surface  of  the  tube  (fig.  61).  In  order  to  make 
contact  with  the  induction  coil,  a  wooden  American  paper- 
clip, lined  with  platinum  foil,  is  made  to  grasp  the  tube ; 
the  foil  is  connected  with  two  strong  loops  of  platinum 
wire,  and  to  these  the  wires  from  the  coil  are  attached 
(fig.  62).  In  this  way  no  strain  is  put  on  the  eudiometer 
wires  by  the  weight  of  the  wires  from  the  coil,  and 
perfect  contact  is  ensured  between  the  foil  and  platinum 
wires.  It  is  also  easy  to  clean  the  outside  of  the 
eudiometer  without  fear  of  injuring  the  instrument. 

It  will  now  be  necessary  to  examine  if  the  glass  is  perfectly 
fused  to  the  wires.     For  this  purpose  the  eudiometer  is     Fig.  56. 
filled  with  mercury,  and  inverted  in  the  trough.     If  the 
tube  has  800  m.m.  divisions,  a  vacuous  space  will  be  formed  in  the 
upper  end.     Note  the  height  of  the  mercury,  and  if  this  remains 
constant  for  a  while  the  wires  are  properly  sealed.     Should  the 


454 


YOLUMETEIC   ANALYSIS. 


§  93. 


eudiometer  be  short,  hold  it  in  the  hands,  and  bring  it  down  with 
a  quick  movement  upon  the  edge  of  the  india-rubber  cushion  at 
the  bottom  of  the  trough,  taking  care  that  the  force  of  impact  is 
slight,  else  the  mercury  may  fracture  the  sealed  end  of  the  tube. 
By  jerking  the  eudiometer  thus,  a  momentary  vacuum  is  formed, 
and  if  there  is  any  leakage,  small  bubbles  of  air  will  arise  from  the 
junction  of  the  wires  with  the  glass. 


Tig.  57. 


Fig.  58. 


Tig.  59. 


Fig.  60. 


Fig.  61. 


Fig.  62. 


tubes  are  graduated  by  the  following  processes : — A  cork 
is  fitted  into  the  end  of  the  tube,  and  a  piece  of  stick,  a  file,  or 
anything  that  will  make  a  convenient  handle,  is  thrust  into  the 
cork.  The  tube  is  heated  over  a  charcoal  fire  or  combustion  furnace, 
and  coated  with  melted  wax  by  means  of  a  camel's-hair  brush. 
Sometimes  a  few  drops  of  turpentine  are  mixed  with  the  wax  to 


§  93. 


APPARATUS   FOR  ANALYSIS   OF  GASES. 


455 


render  it  less  brittle,  but  this  is  not  always  necessary. 

cooling  it  should  be  found  that 

the  layer  of  wax  is  not  uniform, 

the  tube  may  be  placed  in  a 

perpendicular  position  before  a 

tire  and  slowly  rotated  so  as  to 

heat  it  evenly.     The  wax  will 

then  be  evenly  distributed  on 

the  surface  of    the  glass,  the 

excess  flowing  oif.     The  tube 

must  not  be  raised  to  too  high 

a  temperature,  or  the  wax  may 

become  too  thin  ;  but  all  thick 

masses  should  be  avoided,  as 

they  may  prove  troublesome  in 

the  subsequent  operation. 

The  best  and  most  accurate 
mode  of  marking  the  millimeter 
divisions  on  the  wax  is  by  a 
graduating  machine  ;  but  the 
more  usual  process  is  to  copy 
the  graduations  from  another 
tube  in  the  following  manner. 
A  hard  glass  tube,  on  which  « 
millimeter  divisions  have  al- 
ready been  deeply  etched,  is  p 
fixed  in  a  groove  in  the  gra- 
duating table,  a  straight-edge 
of  brass  being  screwed  down 
on  the  tube  and  covering  the 
ends  of  the  lines.  The  standard 
tube  is  shown  in  the  figure  at 
the1  right-hand  end  of  the 
apparatus  (fig.  63).  The 
waxed  tube  is  secured  at  the 
other  end  of  the  same  groove, 
and  above  it  are  fixed  two 
brass  plates,  one  with  a  straight- 
edge, and  the  other  with 
notches  at  intervals  of  5  m.m., 
the  alternate  notches  being 
longer  than  the  intermediate 
ones  (fig.  64).  A  stout  rod  of 
wood  provided  with  a  sharp 
steel  point  near  one  end,  and  a 
penknife  blade  at  the  other 
(fig.  65),  is  held  so  that  the 
steel  point  rests  in  one  of  the 


If, 


on 


8 

bb 

s 


456  VOLUMETRIC   ANALYSIS.  §    93. 

divisions  of  the  graduated  tube,  being  gently  pressed  at  the  same 
time  against  the  edge  of  the  brass  plate ;  the  point  of  the  knife- 
blade  is  then  moved  by  the  operator's  right  hand  across  the  portion 
of  the  waxed  tube  which  lies  exposed  between  the  two  brass  plates. 
When  the  line  has  been  scratched  011  the  wax,  the  point  is  moved 
along  the  tube  until  it  falls  into  the  next  division ;  another  line  is 
now  scratched  on  the  wax,  and  so  on.  At  every  fifth  division  the 
knife-blade  will  enter  the  notches  in  the  brass  plate,  making  a 
longer  line  on  the  tube.  After  a  little  practice  it  will  be  found 
easy  to  do  fifty  or  sixty  divisions  in  a  minute,  and  with  perfect 
regularity.  Before  the  tube  is  removed  from  the  apparatus,  it  must 
be  carefully  examined  to  see  if  any  mistake  has  been  made.  It 
may  have  happened  that  during  the  graduation  the  steel  point 
slipped  out  of  one  of  the  divisions  in  the  standard  tube ;  if 
this  has  taken  place,  it  will  be  found  that  the  distance  between 
the  line  made  at  that  time  and  those  on  each  side  of  it  will 
not  be  equal,  or  a  crooked  or  double  line  may  have  been  produced. 
This  is  easily  obliterated  by  touching  the  wax  with  a  piece  of  heated 
platinum  wire,  after  which  another  line  is  marked.  The  tube  is 
now  taken  out  of  the  table,  and  once  more  examined.  If  any 
portions  of  wax  have  been  scraped  off  by  the  edges  of  the  apparatus, 


Fig.  66. 

or  by  the  screws,  the  coating  must  be  repaired  with  the  hot 
platinum  wire.  Numbers  have  next  to  be  marked  opposite  each 
tenth  division,  beginning  from  the  closed  end  of  the  tube,  the 
first  division,  which  should  be  about  10  m.m.  from  the  end,  being 
marked  10  (see  fig.  60).  The  figures  may  be  well  made  with  a 
steel  pen.  This  has  the  advantage  of  producing  a  double  line 
when  the  nib  is  pressed  against  the  tube  in  making  a  down-stroke. 
The  date,  the  name  of  the  maker  of  the  tube,  or  its  number, 
may  now  be  written  on  the  tube. 

The  etching  by  gaseous  hydrofluoric  acid  is  performed  by 
supporting  the  tube  by  two  pieces  of  wire  over  a  long  narrow 
leaden  trough  containing  sulphuric  acid  and  powdered  fluor-spar 
(fig.  66),  and  the  whole  covered  with  a  cloth  or  sheet  of  paper. 
Of  course  it  is  necessary  to  leave  the  cork  in  the  end  of  the  tube 
to  prevent  the  access  of  hydrofluoric  acid  to  the  interior,  which 
might  cause  the  tube  to  lose  its  transparency  to  a  considerable 
extent.  The  time  required  for  the  action  of  the  gas  varies  with 
the  kind  of  glass  employed.  "With  ordinary  flint  glass  from  ten 
minutes  to  half  an  hour  is  quite  sufficient ;  if  the  leaden  trough  is 
heated,  the  action  may  take  place  even  still  more  rapidly.  The 


93. 


APPARATUS   FOR   ANALYSIS    OF   GASES. 


457 


tube  is  removed  from  time  to  time,  and  a  small  portion  of  the 
Avax  scraped  off  from  a  part  of  one  of  the  lines ;  and  if  the  division 
can  be  felt  with  the  finger-nail  or  the  point  of  a  knife,  the 
operation  is  finished ;  if  not,  the  wax  must  be  replaced,  and  the 
tube  restored  to  the  trough.  When  sufficiently  etched,  the  tube 
is  washed  with  water,  heated  before  a  fire,  and  the  wax  wiped 
off  with  a  warm  cloth. 

The  etching  may  also  be  effected  with  liquid  hydrofluoric  acid, 
by  applying  it  to  the  divisions  on  the  waxed  tube  with  a  brush, 
or  by  placing  the  eudiometer  in  a  gutta-percha  tube  closed  at  one 
end,  and  containing  some  of  the  liquid. 


Fig.  67. 


Fig.  68. 


As  all  glass  tubes  are  liable  to  certain  irregularities  of  diameter, 
it  follows  that  equal  lengths  of  a  graduated  glass  tube  will  not 
contain  exactly  equal  volumes ;  hence  it  is,  of  course,  impossible  to 
obtain  by  measurement  of  length  the  capacity  of  the  closed  end  of 
the  tube. 

In  order  to  provide  for  this,  the  tube  must  be  carefully  calibrated. 
For  this  purpose  it  is  supported  vertically  (fig.  67),  and  successive 
quantities  of  mercury  poured  in  from  a  measure.  This  measure 
should  contain  about  as  much  mercury  as  ten  or  twenty  divisions 
of  the  eudiometer,  and  is  made  of  a  piece  of  thick  glass  tube, 
closed  at  one  end,  and  with  the  edges  of  the  open  end  ground 
perfectly  flat.  The  tube  is  fixed  into  a  piece  of  wood  in  order  to 


458 


VOLUMETRIC   ANALYSIS. 


§    93. 


avoid  heating  its  contents  during  the  manipulation.  The  measure 
may  be  filled  with  mercury  from  a  vessel  closed  with  a  stop-cock 
terminating  in  a  narrow  vertical  tube,  which  is  passed  to  the  bottom 
of  the  measure  (fig.  68).  On  carefully  opening  the  stop-cock  the 
mercury  flows  into  the  measure  without  leaving  any  air-bubbles 
adhering  to  the  sides.  A  glass  plate  is  now  pressed  on  the  ground 
edges  of  the  tube,  which  expels  the  excess  of  mercury  and  leaves 
the  measure  entirely  filled.  The  mercury  may  be  introduced  into 
the  measure  in  a  manner  which  is  simpler  and  as  effectual,  though 
perhaps  not  quite  so  convenient,  by  first  closing  it  with  a  glass 
plate,  and  depressing  it  in  the  mercurial  trough,  removing  the  plate 
from  the  tube,  and  again  replacing  it  before  raising  the  measure 
above  the  surface  of  the  mercury.  After  pouring  each  measured 
quantity  of  mercury  into  the  eudiometer,  the  air-bubbles  are 
carefully  detached  from  the  sides  by  means  of  a  thin  wooden  rod 
or  piece  of  whalebone,  and  the  level  of  the  mercury  at  the  highest 
part  of  the  curved  surface  carefully  observed. 

In  all  measurements 
in  gas  analysis  it  is,  of 
course,  essential  that  the 
eye  should  be  exactly  011 
a  level  with  the  surface 
of  the  mercury,  for  the 
parallax  ensuing  if  this 
were  not  the  case  would 
produce  grave  errors 
in  the  readings.  The 
placing  of  the  eye  in  the 
proper  position  may  be 
ensured  in  two  ways.  A 
small  piece  of  looking- 
glass  (the  back  of  which 
is  painted,  or  covered 
with  paper  to  prevent  the 
accidental  soiling  of  the 
mercury  in  the  trough)  is 
placed  behind,  and  in  contact  with  the  eudiometer.  The  head  is 
now  placed  in  such  a  position  that  the  reflection  of  the  pupil  of 
the  eye  is  precisely  on  a  level  with  the  surface  of  the  mercury  in 
the  tube,  and  the  measurement  made.  As  this  process  necessitates 
the  hand  of  the  operator  being  placed  near  the  eudiometer,  which 
might  cause  the  warming  of  the  tube,  it  is  preferable  to  read  oft* 
with  a  telescope  placed  at  a  distance  of  from  two  to  six  feet  from 
the  eudiometer.  The  telescope  is  fixed  on  a  stand  in  a  horizontal 
position,  and  the  support  is  made  to  slide  on  a  vertical  rod.  The 
image  of  the  surface  of  the  mercury  is  brought  to  the  centre  of 
the  field  of  the  telescope,  indicated  by  the  cross  wires  in  the  eye- 
piece, and  the  reading  taken.  The  telescope  has  the  advantage  of 


69. 


§  93. 


CALIBRATION   OF   INSTRUMENTS. 


459 


magnifying  the  graduations,  and  thus  facilitating  the  estimation 
by  the  eye  of  tenths  of  the  divisions.  Fig.  69  represents  the 
appearance  of  the  tube  and  mercury  as  seen  by  an  inverting 
telescope. 

By  this  method  the  capacity  of  the  tube  at  different  parts  of  its 
length  is  determined.  If  the  tube  were  of  uniform  bore,  each 
measure  of  mercury  would  occupy  the  same  length  in  the  tube ; 
but  as  this  is  never  the  case,  the  value  of  the  divisions  at  all  parts 
of  the  tube  will  not  be  found  to  be  the  same. 

From  the  data  obtained  by  measuring  the  space  in  the  tube 
which  is  occupied  by  equal  volumes  of  mercury,  a  table  is  con- 
structed by  which  the  comparative  values  of  each  millimeter  of  the 
tube  can  be  found.  The  following  results  were  obtained  in  the 
calibration  of  a  short  absorption  eudiometer  : — 

On  the  introduction  of  the  3rd  volume  of  mercury,  the  reading  was  12*8  mm. 
4th  18-4 


5th 
6th 
7th 
8th 


24-0 
29-8 
35-2 
41-0 


Thus,    he  standard  volumes  occupied  5'6  m.m.,  between  12'8  and  18'4 

5-6  „        18-4    „    24-0 

5'8  ,,         24-0    „    29-8 

5'4  ,,         29-8    „    35-2 

5-8  „         35-2    „    41'0 

If  we  assume  the  measure  of  mercury  to  contain  5*8  volumes 
(the  greatest  difference  between  two  consecutive  readings  on  the 
tube),  the  volume  at  the  six  points  above  given  will  be  as  follows  : — 

At  12-8  it  will  be  17'4  or  5-8  x  3 


18-4 
24-0 
29-8 
35-2 
41-0 


23-2  „  5-8x4 

29-0  „  5-8x5 

34-8  „  5-8  x  6 

40-6  „  5-8x7 

46-4  „  5-8  x  8 


Between  the  first  and  second  readings  these  5*8  volumes  are  con- 
tained in  5 -6  divisions,  consequently  each  millimeter  corresponds  to 

— g  =  1  -0357  vol.     This  is  also  the  value  of  the  divisions  between  the 

second  and  third  readings.     Between  the  third  and  fourth  1  m.m. 
contains  1   vol. ;  between  the  fourth  and    fifth,   1   m.m.   contains 

g^  =  1-0741  vol. ;  and  between  the  fifth  and  sixth  m.m.  =  1  vol. 

From  these  data  the  value  of  each  millimeter  on  the  tube  can 
readily  be  calculated.  Thus  13  will  contain  the  value  of  12'8-f- 
the  value  of  0*2  of  a  division  at  this  part  of  the  tube,  or  17 '4  + 
(1-0357x0-2)- 17-60714.  There  is,  however,  no  need  to  go 
beyond  the  second  place  of  decimals,  and,  for  all  practical  purposes, 
the  first  place  is  sufficient.  Thus,  by  adding  or  subtracting  the 
necessary  volumes  from  the  experimental  numbers,  we  find  the 


460 


VOLUMETRIC   ANALYSIS. 


§  93. 


values  of   the   divisions  nearest  to  the  six  points   at  which  the 
readings  were  taken  to  be — 

13-17-61  or  17-6 
18=22-79  „  22-8 
24  =  29-00  „  29-0 
30  =  35-00  „  35-0 
35  =  40-38  „  40-4 
41=46-40  „  46-4 

In  a  precisely  similar  manner  the  values  of   the  intermediate 
divisions  are  calculated,  and  we  thus  obtain  the  following  table :— 


•  1 
I 

Values. 

1 

Values. 

1 

Values. 

0 

H 

1 

1 

10 

14-50 

14-5 

21 

25-89 

25-9 

32 

37-15 

37-1 

11 

15-54 

15-5 

22 

26-93 

26-9 

33 

38-22 

38-2 

12 

16-57 

16-6 

23 

27-96 

28-0 

34 

39-30 

39-3 

13 

17-61 

17-6 

24 

29-00 

29-0 

35 

40-38 

40-4 

14 

18-65 

18-6 

25 

30-00 

30-0 

36 

41-40 

41-4 

15 

19-68 

19-7 

26 

31-00 

31-0 

37 

42-40 

42-4 

16 

20-71 

20-7 

27 

32-00 

32-0 

38 

43-40 

43-4 

17 

21-75 

21-8 

28 

33-00 

33-0 

39 

44-40 

44-4 

18 

22-79 

22-8 

29 

34-00 

34-0 

40 

45-40 

45-4 

19 

23-82 

23-8 

30 

35-00 

35-0 

41 

46-40 

46-4 

20 

24-86 

24-9 

31 

36-07 

36-1 

&c. 

&c. 

&c. 

If  it  be  desired  to  obtain  the  capacity  of  the  tube  in  cubic 
centimeters,  it  is  only  necessary  to  determine  the  weight  of  the 
quantity  of  mercury  the  measure  delivers,  and  the  temperature  at 
which  the  calibration  was  made,  and  to  calculate  the  contents  by 
the  following  formula  : — 

<jx  (1+0-00018150 


13-596V 

in  which  g  represents  the  weight  of  the  mercury  contained  in  the 
measure,  t  the  temperature  at  which  the  calibration  is  made, 
0*0001815  being  the  coefficient  of  expansion  of  mercury  for  each 
degree  centigrade,  V  the  volume  read  off  in  the  eudiometer,  and  C 
the  number  of  cubic  centimeters  required. 

A  correction  has  to  be  made  to  every  number  in  the  table  on 
account  of  the  surface  of  the  mercury  assuming  a  convex  form  in 
the  tube.  During  the  calibration,  the  convexity  of  the  mercury  is 
turned  towards  the  open  end  of  the  tube  (fig.  70),  whilst  in  the 


93. 


CALIBRATION   OF   INSTRUMENTS. 


461 


measurement  of  a  gas  the  convexity  will  be  in  the  opposite  direction 
(fig.  71).  It  is  obvious  that  the  quantity  of  mercury  measured 
during  the  calibration,  while  the  eudiometer  is  inverted,  will  be 
less  than  a  volume  of  gas  contained  in  the  tube  when  the  mercury 
stands  at  the  same  division,  while  the  eudiometer  is  erect.  The 
necessary  amount  of  correction  is  determined  by  observing  the 
position  of  the  top  of  the  meniscus,  and  then  introducing  a  few 
drops  of  a  solution  of  corrosive  sublimate,  which  will  immediately 
cause  the  surface  of  the  mercury  to  become  horizontal  (fig.  72),  and 
again  measuring. 

It  will  be  observed  that  in  fig.  71  the  top  of  the  meniscus  was 
at  the  division  39,  whereas  in  fig.  72,  after  the  addition  of  corrosive 
sublimate,  the  horizontal  surface  of  the  mercury  stands  at  38 '7, 
giving  a  depression  of  0'3  m.m.  If  the  tube  were  now  placed 
erect,  and  gas  introduced  so  that  the  top  of  the  meniscus  was  at  39, 


*Fig.  70. 


*Fig.  71. 


Pig.  72. 


and  if  it  were  now  possible  to  overcome  the  capillarity,  the  horizontal 
surface  would  stand  at  3 9 '3.  The  small  cylinder  of  gas  between 
38'7  and  39*3,  or  0*6  division,  would  thus  escape  measurement. 
This  number  0*6  is  therefore  called  the  error  of  meniscus,  and  must 
be  added  to  all  readings  of  gas  in  the  eudiometer.  The  difference, 
therefore,  between  the  two  readings  is  multiplied  by  two,  and  the 
volume  represented  by  the  product  obtained — the  error  of  meniscus 
— is  added  to  the  measurements  before  finding  the  corresponding 
capacities  by  the  table.  In  the  case  of  the  tube,  of  which  the 
calibration  is  given  above,  the  difference  between  the  two  readings 
was  0'4  m.m.,  making  the  error  of  meniscus  O8. 

All  experiments  on  gas  analysis,  with  the  apparatus  described, 


*  In  these  the  mercury  should  just  touch  39. 


462 


VOLUMETRIC   ANALYSIS. 


§    93. 


should  be  conducted  in  a  room  set  apart  for  the  purpose,  with  the 
window  facing  the  north,  so  that  the  sun's  rays  cannot  penetrate 
into  it,  and  carefully  protected  from  flues  or  any  source  of  heat 
which  might  cause  a  change  of  temperature  of  the  atmosphere. 
The  mercury  employed  should  be  purified,  as  far  as  possible,  from 
lead  and  tin,  which  may  be  done 
by  leaving  it  in  contact  with  dilute 
nitric  acid  in  a  shallow  vessel  for 
some  time,  or  by  keeping  it  when 
out  of  use  under  concentrated 
sulphuric  acid,  to  which  some  mer- 
curous  sulphate  has  been  added. 
This  mercury  reservoir  may  con- 
veniently be  made  of  a  glass  globe 
with  a  neck  at  the  top  and  a 
stop-cock  at  the  bottom  (fig.  73), 
and  which  is  not  filled  more  than 
one-half,  so  as  to  maintain  as  large 
a  surface  as  possible  in  contact 
with  the  sulphuric  acid.  Any 
foreign  metals  (with  the  exception 
of  silver,  gold,  and  platinum) 
which  may  be  present  are  removed 
by  the  mercurous  sulphate,  an 
equivalent  quantity  of  mercury 
being  precipitated.  This  process, 
which  was  originated  by  M. 
Deville,  has  been  in  use  for 
many  years  with  very  satisfactory 
results,  the  mercury  being  always 
clean  and  dry  when  drawn  from 
the  stop-cock  at  the  bottom  of  the 
globe.  The  mouth  of  the  globe 
should  be  kept  close  to  prevent 
the  absorption  of  water  by  the 
sulphuric  acid. 

In  all  cases,  where  practicable, 
gases  should  be  measured  when 
completely  saturated  with  aqueous 
vapour :  to  ensure  this,  the  top 
of  the  eudiometer  and  absorption 
tubes  should  be  moistened  before 
the  introduction  of  the  mercury. 
This  may  be  done  by  dipping  the  end  of  a  piece  of  iron  wire 
into  water,  and  touching  the  interior  of  the  closed  extremity  of 
the  tube  with  the  point  of  the  wire. 

In  filling  the  eudiometer,  the  greatest  care  must  of  course  be 
taken  to  exclude  all   air-bubbles  from  the  tubes.      This  may  be 


Fig.  73. 


§  93. 


THE   EUDIOMETER. 


463 


effected  in  several  ways :  the  eudiometer  may  be  held  in  an  inverted 
or  inclined  position,  and  the  mercury  introduced  through  a  narrow 
glass  tube  which  passes  to  the  end  of  the  eudiometer  and  com- 
municates, with  the  intervention  of  a  stop-cock,  with  a  reservoir 
of  mercury  (fig.  74).  On  carefully  opening  the  stop-cock,  the 
mercury  slowly  flows  into  the  eudiometer,  entirely  displacing  the  air. 
The  same  result  may  be  obtained  by  placing  the  eudiometer  nearly 
in  a  horizontal  position,  and  carefully  introducing  the  mercury 
from  a  test-tube  without  a  rim  (fig.  75).  Any  minute  bubbles 
adhering  to  the  side  may  generally  be  removed  by  closing  the 
mouth  of  the  tube  with  the  thumb,  and  allowing  a  small  air-bubble 
to  rise  in  the  tube,  and  thus  to  wash  it  out.  After  filling  the 
eudiometer  entirely  with  mercury,  and  inverting  it  over  the  trough, 
it  will  generally  be  found  that  the  air-bubbles  have  been  removed. 

For  the  introduction  of  the  gases,  the  eudiometer  should  be 
placed  in  a  slightly  inclined  position,  being  held  by  a  support 
attached  to  the  mercurial  trough  (fig.  76),  and  the  gas  transferred 

HUBcKT  DYER. 


from  the  tube  in  which  it  has  been  collected.  The  eudiometer  is 
now  put  in  an  absolutely  vertical  position,  determined  by  a 
plumb-line  placed  near  it,  and  a  thermometer  suspended  in  close 
proximity.  It  must  then  be  left  for  at  least  half  an  hour,  no  one 
being  allowed  to  enter  the  room  in  the  meantime.  After  the 
expiration  of  this  period,  the  operator  enters  the  room,  and,  by 
means  of  the  telescope  placed  several  feet  from  the  mercury  table, 
carefully  observes  the  height  of  the  mercury  in  the  tube,  estimating 
the  tenths  of  a  division  with  the  eye,  which  can  readily  be  done 
after  a  little  practice.  He  next  reads  the  thermometer  with  the 
telescope,  and  finally  the  height  of  the  mercury  in  the  trough  is  read 
off  on  the  tube,  for  which  purpose  the  trough  must  have  glass  sides. 
The  difference  between  these  two  numbers  is  the  length  of  the 
column  of  mercury  in  the  eudiometer,  and  has  to  be  subtracted 
from  the  reading  of  the  barometer.  It  only  remains  to  take  the 
height  of  the  barometer.  The  most  convenient  form  of  instrument 
for  gas  analysis  is  the  syphon  barometer,  with  the  divisions  etched 


464 


VOLUMETRIC   ANALYSIS. 


93. 


on  the  tube.  This  is  placed  on  the  mercury  table,  so  that  it  may 
be  read  by  the  telescope  immediately  after  the  measurements 
in  the  eudiometer.  There  are  two  methods  of  numbering  the 
divisions  on  the  barometer :  in  one  the  zero  point  is  at  or 
near  the  bend  of  the  tube,  in  which  case  the  height  of  the 
lower  column  must  be  subtracted 
from  that  of  the  higher;  in  the  other 
the  zero  is  placed  near  the  middle  of 
the  tube,  so  that  the  numbers  have  to 
be  added  to  obtain  the  actual  height. 
In  cases  of  extreme  accuracy,  a  correction 
must  be  made  for  the  temperature  of  the 
barometer,  which  is  determined  by  a  ther- 
mometer suspended  in  the  open  limb  of  the 
instrument,  and  passing  through  a  plug  of 
cotton  wool.  Just  before  observing  the 
height  of  the  barometer,  the  bulb  of  the 
thermometer  is  depressed  for  a  moment 
into  the  mercury  in  the  open  limb,  thus 
causing  a  movement  of  the  mercurial 
column,  which  overcomes  any  tendency 
that  it  may  have  to  adhere  to  the  glass. 

In  every  case  the  volume  observed  must 
be  reduced  to  the  normal  temperature  and 
pressure,  in  order  to  render  the  results 
comparable.  If  the  absolute  volume  is 
required,  the  normal  pressure  of  760  m.m. 
must  be  employed :  but  when  comparative 
volumes  only  are  desired,  the  pressure  of 
1000  m.m.  is  generally  adopted,  as  it 
somewhat  simplifies  the  calculation.  In 
the  following  formula  for  correction  of  the 
volume  of  gases — 

V1  =  the  correct  volume. 

Y  =  the  volume  found  in  the  table,  and 
corresponding  to  the  observed  height  of 
the  mercury  in  the  eudiometer,  the  error 
of  meniscus  being,  of  course,  included. 

B  =  the  height  of  the  barometer  (cor- 
rected for  temperature,  if  necessary)  at 
the  time  of  measurement. 

b  =  the  difference  between  the  height  of  the  mercury  in  the 
trough  and  in  the  eudiometer. 

t  =  the  temperature  in  centigrade  degrees. 

T  =  the  tension  of  aqueous  vapour  in  millimeters  of  mercury 
at  t°.  This  number  is,  of  course,  only  employed  when  the  gas  is 
saturated  with  moisture  at  the  time  of  measurement. 


§93.       CORRECTIONS  FOR  TEMPERATURE  AND  PRESSURE.        465 

Then 

Vx(B-fc-T) 


760  x  (1+0-003665*)' 
when  the  pressure  of  760  ni.m.  is  considered  the  normal  one ;  or, 

Y  x  (B  - 1  -  T) 
~  1000  x  (1+0-003665*)' 

when  the  normal  pressure  of  1  meter  is  adopted. 

In  cases  where  the  temperature  at  measurement  is  below  0° 
(which  rarely  happens),  the  factor  1  -  0*003665*  must  be  used. 

Tables  have  been  constructed  containing  the  values  of  T ;  of 
1000  x  (1  +  0-003665*),  and  of  760  x  (1  +  0-003665*),  which 
very  much  facilitate  the  numerous  calculations  required  in  this 
branch  of  analysis.*  These  will  be  found  at  the  end  of  the  book. 


Fig.  76. 

We  shall  now  be  in  a  position  to  examine  the  methods  employed 
in  gas  analysis.  Some  gases  may  be  estimated  directly ;  that  is, 
they  may  be  absorbed  by  certain  reagents,  the  diminution  of  the 
volume  indicating  the  quantity  of  the  gas  present.  Some  are 
determined  indirectly ;  that  is,  by  exploding  them  with  other 
gases,  and  measuring  the  quantities  of  the  products.  Some  gases 
may  be  estimated  either  directly  or  indirectly,  according  to  the 
circumstances  under  which  they  are  found. 

*  Mr.  Sutton  will  forward  a  copy  of  these  Tables,  printed  separately  for  laboratory 
use,  to  any  one  desiring  them,  on  receipt  of  the  necessary  address. 

II   II 


466  VOLUMETRIC  ANALYSIS.  §    95. 

§  94. 

1.     GASES    ESTIMATED    DIRECTLY. 

A.  Gases  Absorbed  by  Crystallized  Sodic  Phosphate  and  Potassic 

Hydrate  :— 

Hydrochloric  acid, 
Hydrobromic  acid, 
Hydriodic  acid. 

B.  Gases  Absorbed  by  Potassic  Hydrate,  and  not  by  Crystallized 

Sodic   Phosphate:— 

Carbonic  anhydride, 
Sulphurous  anhydride, 
Hydrosulphuric  acid. 

C.  Gases   Absorbed   by  neither   Crystallized   Sodic   Phosphate    nor 

Potassic   Hydrate:— 

Oxygen, 
Nitric  oxide, 
Carbonic  oxide, 

Hydrocarbons  of  the  composition  Cn  H2n, 
Hydrocarbons  of  the  formula  (Cn  H2n  +  l)2, 
Hydrocarbons    of    the    formula    Cn    H2n  +  2, 
except  Marsh  gas. 

2.     GASES    ESTIMATED    INDIRECTLY. 

Hydrogen, 
Carbonic  oxide, 
Marsh  gas, 
Methyl, 

Ethylic  hydride, 
Ethyl, 

Propylic  hydride, 
Butylic  hydride, 
Nitrogen. 

DIRECT    ESTIMATIONS. 

Group  A,   containing-  Hydrochloric,  Hydrobromic,  and 
Hydriodic   Acids. 

§  95.  IN  Buns  en's  method  the  reagents  for  absorption  are 
generally  used  in  the  solid  form,  in  the  shape  of  bullets.  To  make 
the  bullets  of  sodic  phosphate,  the  end  of  a  piece  of  platinum  wire, 
of  about  one  foot  in  length,  is  coiled  up  and  fixed  in  the  centre  of 
a  pistol-bullet  mould.  It  is  well  to  bend  the  handles  of  the  mould, 


§    95.  DIRECT  ESTIMATIONS.  467 

so  that  when  it  is  closed  the  handles  are  in  contact,  and  may  be 
fastened  together  by  a  piece  of  copper  wire  (fig.  77).  The  usual 
practice  is  to  place  the  platinum  wire  in  the  hole  through  which  the 
mould  is  filled ;  but  it  is  more  convenient  to  file  a  small  notch  in 
one  of  the  faces  of  the  open  mould,  and  place  the  wire  in  the  notch 
before  the  mould  is  closed.  In  this  manner  the  wire  is  not  in  the 
way  during  the  casting,  and  it  is  subsequently  more  easy  to  trim 
the  bullet.  Some  ordinary  crystallized  sodic  phosphate  is  fused  in 
a  platinum  crucible  (or  better,  in  a  small  piece  of  wide  glass  tube, 
closed  at  one  end,  and  with  a  spout  at  the  other,  and  held  by  a 
copper-wire  handle),  and  poured  into  the  bullet  mould  (fig.  78). 
When  quite  cold,  the  mould  is  first  gently  warmed  in  a  gas-flame, 
opened,  and  the  bullet  removed.  If  the  warming  of  the  mould  is 
omitted,  the  bullet  is  frequently  broken  in  consequence  of  its 
adhering  to  the  metal.  Some  chemists  recommend  the  use  of  sodic 
sulphate  instead  of  phosphate,  which  may  be  made  into  balls  by 
dipping  the  coiled  end  of  a  piece  of  platinum  wire  into  the  salt 


Fig.  77.  Pig.  78. 

fused  in  its  water  of  crystallization.  On  removing  the  wire,  a 
small  quantity  of  the  salt  will  remain  attached  to  the  wire.  When 
this  has  solidified,  it  is  again  introduced  for  a  moment  and  a 
larger  quantity  will  collect :  and  this  is  repeated  until  the  ball  is 
sufficiently  large.  The  balls  must  be  quite  smooth,  in  order  to 
prevent  the  introduction  of  any  air  into  the  eudiometer.  When 
the  bullets  are  made  in  a  mould,  it  is  necessary  to  remove  the 
short  cylinder  which  is  produced  by  the  orifice  through  which  the 
fused  salt  has  been  poured. 

In  the  estimation  of  these  gases,  it  is  necessary  that  they  should 
be  perfectly  dry.  This  may  be  attained  by  introducing  a  bullet  of 
fused  calcic  chloride.  After  the  lapse  of  about  an  hour,  the  bullet 
may  be  removed,  the  absorption  tube  placed  in  a  vertical  position, 
with  thermometer,  etc.,  arranged  for  the  reading,  and  left  for 
half  an  hour  to  assume  the  temperature  of  the  air.  When  the 
reading  has  been  taken,  one  of  the  bullets  of  sodic  phosphate  or 
sodic  sulphate  is  depressed  in  the  trough,  wiped  with  the  fingers 

H  H  2 


468 


VOLUMETEIC   ANALYSIS. 


96. 


while  under  the  mercury  in  order  to  remove  any  air  that  it  might 
have  carried  down  with  it,  and  introduced  into  the  absorption  tube, 
which  for  this  purpose  is  inclined  and  held  in  one  hand,  while 
the  bullet  is  passed  into  the  tube  with  the  other.  Care  must  be 
taken  that  the  whole  of  the  platinum  wire  is  covered  with  mercury 
while  ,the  bullet  remains  in  the  gas,  otherwise  there  is  a  risk  of 
air  entering  the  tube  between  the  mercury  and  the  wire  (fig.  79). 

After  standing  for  an  hour,  the  bullet  is  withdrawn  from  the 
absorption  tube.  This  must  be  done  with  some  precaution,  so  as 
to  prevent  any  gas  being  removed  from  the  tube.  It  is  best  done 
by  drawing  down  the  bullet  by  a  brisk  movement  of  the  wire,  the 
gas  being  detached  from  the  bullet  during  the  rapid  descent  of  the 
latter  into  the  mercury.  The  bullet  may  then  be  more  slowly 
removed  from  the  tube.  As  sodic  phosphate  and  sodic  sulphate 
contain  water  of  crystallization,  and  a  corresponding  proportion, 
of  this  is  liberated  for  every  equivalent  of  sodic  chloride  formed, 
care  must  be  taken  that  the 
bullets  are  not  too  small,  else 
the  water  set  free  will  soil  the 
sides  of  the  eudiometer,  especially 
if  there  is  a  large  volume  of  gas 
to  be  absorbed.  As  a  further 
precaution,  drive  off  some  of  the 
water  of  crystallization  before 
casting  the  bullet.  When  the 
bullet  has  been  removed,  the  gas 
must  be  dried  as  before  with 
calcic  chloride  and  again  measured. 
If  two  or  more  of  the  gases  are 
present  in  the  mixture  to  be 
analyzed,  the  sodic  phosphate  ball 
must  be  dissolved  in  water,  and 
the  chlorine,  bromine,  and  iodine 
determined  by  the  ordinary  ana- 
lytical methods.  If  this  has  to 
be  done,  care  must  be  taken 
that  the  sodic  phosphate  employed  is  free  from  chlorine. 


Group  B.    Gases  absorbed  by  Potassic  Hydrate,  but  not  by 
Sodic   Phosphate. 

Carbonic    anhydride,    sulphuretted    hydrogen,    and 
sulphurous    anhydride. 

§  96.  IF  the  gases  occur  singly,  they  are  determined  by  means 
of  a  bullet  of  caustic  potash  made  in  the  same  manner  as  the  sodic 
phosphate  balls.  The  caustic  potash  employed  should  contain 
sufficient  water  to  render  the  bullets  so  soft  that  they  may  be 


§    96.  POTASH  ABSORPTIONS.  469 

marked  with  the  nail  when  cold.  Before  use  the  balls  must  be 
slightly  moistened  with  water ;  and  if  large  quantities  of  gas  have 
to  be  absorbed,  the  bullet  must  be  removed  after  some  hours, 
washed  with  water,  and  returned  to  the  absorption  tube.  The 
absorption  may  extend  over  twelve  or  eighteen  hours.  In  order  to 
ascertain  if  it  is  completed,  the  potash  ball  is  removed,  washed, 
again  introduced,  and  allowed  to  remain  in  contact  with  the  gas 
for  about  an  hour.  If  no  diminution  of  volume  is  observed  the 
operation  is  finished. 

The  following  analyses  of  a  mixture  of  air  and  carbonic  anhydride 
will  serve  to  show  the  mode  of  recording  the  observations  and  the 
methods  of  calculation  required. 


Analysis   of  a   Mixture   of  Air  and   Carbonic   Anhydride. 
1.     Gas  Saturated  with  Moisture. 

Height  of  mercury  in  trough   .              =  171*8  m.m. 

Height  of  mercury  in  absorption  eudio- 
meter           .             .             .  89-0  m.m. 

Column  of  mercury  in  tube,  to  be  sub-  

tracted  from  the  height  of  barometer  =  b  =   82 '8  m.m. 

Height  of  mercury  in  eudiometer          =  89"0  m.m. 

Correction  for  error  of  meniscus  0'8  m.m. 

89-8  m.m. 
Volume  in  table  corresponding  to  89*8 

m.m.  .  .  .  =  V  =  96-4 

Temperature  at  which  the  reading  was 

made  .  .  .  =   t   =  12'2° 

Height  of  barometer  at  time  of  obser- 
vation .  .  .  =B  =  765-25  m.m. 
Tension  of  aqueous  vapour  at  12*2°       =T=      10'6  m.m. 
V  x  (B  -  b  -  T) 


V*  = 


1000  x  (1+0-003665^)" 
96-4  x  (765-25 -82-8 -10-6) 
1000  x  [1  +  (0-003665  x  12'2)] 
96-4x671-85 


1000x1-044713 


=  61-994 


log.    96-4   =1-98408 

log.  671-85  =  2-82727 

4-81135 
log.  (1000x1-044713)  =  3-01900 

1-79235  =  log.  61-994  =  V1 
Corrected  volume  of  air  and  C02  =  Vx=  61 '994. 


4*70                                   VOLUMETRIC   ANALYSIS.  §    9 

After  absorption  of   carbonic  anhydride  by  bullet  of 
potassic  hydrate. 

Gas  Dry. 

Height  of  mercury  in  trough   .  172'0  m.m. 
Height  of  mercury  in  absorption  eudio- 
meter           .             .             .  62'5  m.m. 

Column  of  mercury  in  eudiometer         =  1>  =  109 '5  m.m. 

Height  of  mercury  in  eudiometer  6 2 '5  m.m. 

Correction  for  error  of  meniscus            =  0'8  m.m. 


63-3 


m.m. 


Volume  in  table  corresponding  to  63*3 

m.m.  .  .  .  =  V  =  69 '35 

Temperature    .  .  .  =   t   =  10 '8° 

Barometer        .  .  .  =  B  =  766'0  m.m. 


1000  x  (1+0-003665^)" 

69-35  x  (766-0 -109-5) 
1000  x[l+  (0-003665x10-8)] 

69-35x656-5 


1000x1-039582 


43-795 


log.    69*35=1-84105 
log.  656-5   =2-81723 

4-65828 
log.  (1000x1-039582)  =3-01686 

1-64142  =  log.  43-795  =  V* 

Corrected  volume  of  air  =  43*795 
Air  +  CO2  =61  *994 
Air  =43*795 

C02=  18*199 

61-994     :     18*199     :  :     100     :     x  =  percentage  of  CO2 
_18*199xlQO_ 
61-995 

Percentage  of  CO2  in  mixture  of  air  and  gas  =  29*355. 


8    96.  POTASH  ABSORPTIONS.  471 

o 

Gas  Moist. 

Height  of  mercury  in  trough   .  174-0  m.m. 

Height  of  mercury  in  eudiometer  98 '0  m.m. 

Column  of  mercury  in  tube      ,  =  b  =  76'Q  m.m. 

Height  of  mercury  in  eudiometer  98*0  m.m. 

Correction  for  error  of  meniscus  0*8  m.m. 

98-8  m.m. 

Volume  in  table,  corresponding  to  9 8 '8 

m.m.  .  .  .  =V=  105-6 

Temperature    .  .  .  =  £=    12'5° 

Barometer        .  .  .  •  =B=  738'0  m.m. 

Tension  of  aqueous  vapour  at  12 '5°      =T=    10 '8  m.m. 

Corrected  volume  of  air  and  carbonic 

anhydride  .  .  .  6  5 '7  54 

After  absorption  of   CO2. 
Gas  Dry. 

Height  of  mercury  in  trough  .  173'0  m.rn. 

Height  of  mercury  in  absorption  eudio- 
meter ...  70*3  m.m. 

Column  of  mercury  in  tube      .  =  b  =  102 '7  m.m. 

Height  of  mercury  in  eudiometer  70 '3  m.m. 

Correction  for  error  of  meniscus  0'8  m.m. 

71-1  m.m. 

Volume  in  table  corresponding  to  71*1 

m.m.  .  .  .  =V=    77 '4 

Temperature    .  .  .  =  t  =    14'1° 

Barometer        .  .  .  =  B=733'5m.m. 

Corrected  volume  of  air  =  46 '425 

Air  +  CO2  =  65-754 

Air  =46-425 

CO2  =19-329 

65-754  :  19*329  :  :  100  :  22-396. 

i.  ii. 

Percentage  of  CO2  in  mixture  of  air  and  gas    29*355    29'396 

If  either  sulphurous  anhydride  or  sulphuretted  hydrogen  occurs 
together  with  carbonic  anhydride,  one  or  two  modes  of  operation 
may  be  followed.  Sulphuretted  hydrogen  and  sulphurous  anhydride 
are  absorbed  by  manganic  peroxide  and  by  ferric  oxide,  which 
may  be  formed  into  bullets  in  the  following  manner.  The  oxides 


472  VOLUMETRIC  ANALYSIS.  §    96. 

are  made  into  a  paste  with  water,  and  introduced  into  a  bullet 
mould,  the  interior  of  which  has  been  oiled,  and  containing  the 
coiled  end  of  a  piece  of  platinum  wire ;  the  mould  is  then  placed 
on  a  sand  bath  till  the  ball  is  dry.  The  oxides  will  now  be  left  in 
a  porous  condition,  which  would  be  inadmissible  for  the  purpose 
to  which  they  are  to  be  applied ;  the  balls  are  therefore  moistened 
several  times  with  a  sirupy  solution  of  phosphoric  acid,  care  being 
taken  that  they  do  not  become  too  soft,  so  as  to  render  it  difficult 
to  introduce  them  into  the  eudiometer.  After  the  sulphuretted 
hydrogen  or  sulphurous  anhydride  has  been  removed,  the  gas 
should  be  dried  by  means  of  calcic  chloride.  The  carbonic 
anhydride,  can  now  be  determined  by  means  of  the  bullet  of 
potassic  hydrate. 

The  second  method  is  to  absorb  the  two  gases  by  means  of 
a  ball  of  potassic  hydrate  containing  water,  but  not  moistened  011 
the  exterior,  then  to  dissolve  the  bullet  in  dilute  acetic  acid  which 
has  been  previously  boiled  and  allowed  to  cool  without  access  of 
air,  and  to  determine  the  amount  of  sulphuretted  hydrogen  or 
sulphurous  anhydride  by  means  of  a  standard  solution  of  iodine. 
This  process  is  especially  applicable  when  rather  small  quantities  of 
sulphuretted  hydrogen  have  to  be  estimated. 


Group  C.  This  group  contains  the  gases  not  absorbed  by  Potassic 
Hydrate  or  Sodic  Phosphate,  and  consists  of  Oxygen,  Nitric 
Oxide,  Carbonic  Oxide,  Hydrocarbons  of  the  formulae  CnH:n 
2,  and  CnH^n  +  s,  except  Marsh  gas. 


Oxygen  was  formerly  determined  by  means  of  a  ball  of 
phosphorus,  but  it  is  difficult  subsequently  to  free  the  gas  from 
the  phosphorous  acid  produced,  and  which  exerts  some  tension,  and 
so  vitiates  the  results  ;  besides  which,  the  presence  of  some  gases 
interferes  with  the  absorption  of  oxygen  by  phosphorus  ;  and  if 
any  potassic  hydrate  remains  on  the  side  of  the  tube,  from  the 
previous  absorption  of  carbonic  anhydride,  there  is  a  possibility  of 
the  formation  of  phosphoretted  hydrogen,  which  would,  of  course, 
vitiate  the  analysis.  A  more  convenient  reagent  is  a  freshly 
prepared  alkaline  solution  of  potassic  pyrogallate  introduced  into 
the  gas  in  a  bullet  of  papier-mache.  The  balls  of  papier-mache 
are  made  by  macerating  filter-paper  in  water,  and  forcing  as  much 
of  it  as  possible  into  a  bullet  mould  into  which  the  end  of  a  piece 
of  platinum  wire  has  been  introduced.  In  order  to  keep  the  mould 
from  opening  while  it  is  being  filled,  it  is  well  to  tie  the  handles 
together  with  a  piece  of  string  or  wire,  and  when  charged  it  is 
placed  on  a  sand  bath.  After  the  mass  is  dry  the  mould  may  be 
opened,  when  a  large  absorbent  bullet  will  have  been  produced. 
The  absorption  of  oxygen  by  the  alkaline  pyrogallate  is  not  very 
rapid,  and  it  may  be  necessary  to  remove  the  ball  once  or  twice 
during  the  operation,  and  to  charge  it  freshly. 


§    96.  OXYGEN  ABSORPTION.  473 

Nitric  oxide  cannot  be  readily  absorbed  in  an  ordinary 
absorption  tube ;  it  may,  however,  be  converted  into  nitrous 
anhydride  and  nitric  peroxide  by  addition  of  excess  of  oxygen, 
absorbing  the  oxygen  compounds  with  potassic  hydrate,  and  the 
excess  of  oxygen  by  potassic  pyrogallate.  The  diminution  of  the 
volume  will  give  the  quantity  of  nitric  oxide.  This  process  is 
quite  successful  when  the  nitric  oxide  is  mixed  with  olefiant  gas 
and  ethylic  hydride,  but  it  is  possible  that  other  hydrocarbons 
might  be  acted  on  by  the  nitrous  compounds. 

Carbonic  oxide  may  be  absorbed  by  two  reagents.  If  carbonic 
anhydride  and  oxygen  be  present  they  must  be  absorbed  in  the 
usual  manner,  and  afterwards  a  papier-mache  ball  saturated  with 
a  concentrated  solution  of  cuprous  chloride  in  dilute  hydrochloric 
acid  introduced.  A  ball  of  caustic  potash  is  subsequently  employed 
to  remove  the  hydrochloric  acid  given  off  by  the  previous  reagent, 
and  to  dry  the  gas.  Carbonic  oxide  may  also  be  absorbed  by 
introducing  a  ball  of  potassic  hydrate,  placing  the  absorption  tube 
in  a  beaker  of  mercury,  and  heating  the  whole  in  a  water  bath  to 
100°  for  60  hours.  The  carbonic  oxide  is  thus  converted  into 
potassic  formate  and  entirely  absorbed. 

Olefiant  Gas  and  other  Hydrocarbons  of  the  formula 
CnH2n  are  absorbed  by  Nordhausen  sulphuric  acid,  to  which  an 
additional  quantity  of  sulphuric  anhydride  has  been  added.  Such 
an  acid  may  be  obtained  by  heating  some  Xordhausen  acid  in 
a  retort  connected  with  a  receiver  containing  a  small  quantity  of 
the  same  acid.  This  liquid  is  introduced  into  the  gas  by  means  of 
a  dry  coke  bullet.  These  bullets  are  made  by  filling  the  mould, 
into  which  the  usual  platinum  wire  has  been  placed,  with  a  mixture 
of  equal  weights  of  finely  powdered  coke  and  bituminous  coal. 
The  mould  is  then  heated  as  rapidly  as  possible  to  a  bright  red 
heat,  and  opened  after  cooling ;  a  hard  porous  ball  will  have  been 
produced,  which  may  be  employed  for  many  different  reagents. 
It  is  sometimes  difficult  to  obtain  the  proper  mixture  of  coal  and 
coke,  but  when  once  prepared,  the  bullets  may  be  made  with  the 
greatest  ease  and  rapidity.  The  olefiant  gas  will  be  absorbed  by  the 
sulphuric  acid  in  about  an  hour,  though  they  may  be  left  in  contact 
for  about  two  hours  with  advantage.  If,  on  removing  the  bullet, 
it  still  fumes  strongly  in  the  air,  it  may  be  assumed  that  the 
absorption  is  complete.  The  gas  now  contains  sulphurous,  sulphuric, 
and  perhaps  carbonic  anhydrides ;  these  may  be  removed  by 
a  manganic  peroxide  ball,  followed  by  one  of  potassic  hydrate,  or 
the  former  may  be  omitted,  the  caustic  potash  alone  being  used. 
The  various  members  of  the  CnH2n  group  cannot  be  separated 
directly,  but  by  the  indirect  method  of  analysis  their  relative 
quantities  in  a  mixture  may  be  determined. 

The  hydrocarbons  (CnH2n  +  *)2  and  CnH2n  +  2maybe  absorbed 
by  absolute  alcohol,  some  of  which  is  introduced  into  the 
absorption  tube,  and  agitated  for  a  short  time  with  the  gas. 


474  VOLUMETKIC   ANALYSIS.  §    97. 

Correction  has  then  to  be  made  for  the  weight  of  the  column  of 
alcohol  on  the  surface  of  the  mercury,  and  for  the  tension  of  the 
alcohol  vapour.  This  method  only  gives  approximate  results,  and 
can  only  be  employed  in  the  presence  of  gases  very  slightly  soluble 
in  alcohol. 

The  time  required  in  the  different  processes  of  absorption  just 
described  is  considerable ;  perhaps  it  might  be  shortened  by 
surrounding  the  absorption  eudiometer  with  a  wider  tube,  similar 
to  the  external  tube  of  a  Liebig's  condenser,  and  through  which 
a  current  of  water  is  maintained.  By  means  of  a  thermometer  in 
the  space  between  the  tubes  the  temperature  of  the  gas  would  be 
known,  and  the  readings  might  be  taken  two  or  three  minutes 
after  the  withdrawal  of  the  reagents.  Besides  this  advantage,  the 
great  precaution  necessary  for  maintaining  a  constant  temperature 
in  the  room  might  be  dispensed  with.  A  few  experiments  made 
some  years  ago  in  this  direction  gave  satisfactory  results. 

INDIRECT    DETERMINATIONS. 

§  97.  GASES  which  are  not  absorbed  by  any  reagents  that  are 
applicable  in  eudiometers  over  mercury,  must  be  determined  in  an 
indirect  manner,  by  exploding  them  with  other  gases,  and  noting 
either  the  change  of  volume  or  the  quantity  of  their  products 
of  decomposition;  or  lastly,  as  is  most  frequently  the  case,  by 
a  combination  of  these  two  methods.  Thus,  for  example,  oxygen 
may  be  determined  by  exploding  with  excess  of  hydrogen,  and 
observing  the  contraction ;  hydrogen  may  be  estimated  by  exploding 
with  excess  of  oxygen,  and  measuring  the  contraction ;  and  marsh 
gas  by  exploding  with  oxygen,  measuring  the  contraction,  and  also 
the  quantity  of  carbonic  anhydride  generated. 

The  operation  is  conducted  in  the  following  manner  : — The  long 
eudiometer  furnished  with  explosive  wires  is  filled  with  mercury 
(after  a  drop  of  water  has  been  placed  at  the  top  of  the  tube  by 
means  of  an  iron  wire,  as  before  described),  and  some  of  the  gas  to 
be  analyzed  is  introduced  from  the  absorption  eudiometer.  This 
gas  is  then  measured  with  the  usual  precautions,  and  an  excess  of 
oxygen  or  hydrogen  (as  the  case  may  be)  introduced.  These  gases 
may  be  passed  into  the  eudiometer  directly  from  the  apparatus  in 
which  they  are  prepared ;  or  they  may  be  previously  collected  in 
lipped  tubes  of  the  form  of  absorption  tubes,  so  as  to  be  always 
ready  for  use. 

For  the  preparation  of  the  oxygen  a  bulb  is  iised,  which  is  blown 
at  the  closed  end  of  a  piece  of  combustion  tube.  The  bulb  is  about 
half  filled  with  dry  powdered  potassic  chlorate,  the  neck  drawn  out, 
and  bent  to  form  a  delivery  tube.  The  chlorate  is  fused,  and  the 
gas  allowed  to  escape  for  some  time  to  ensure  the  expulsion  of  the 
atmospheric  air ;  the  end  of  the  delivery  tube  is  then  brought 
under  the  orifice  of  the  eudiometer,  and  the  necessary  quantity  of 


§  97. 


INDIRECT  DETERMINATIONS. 


475 


gas  admitted.  When  it  is  desired  to  prepare  tlie  oxygen  beforehand, 
it  may  be  collected  directly  from  the  bulb ;  or,  another  method  to 
obtain  the  gas  free  from  air  may  be  adopted  by  those  who  are 
provided  with  the  necessary  appliances.  This  is,  to  connect  a  bulb 
containing  potassic  chlorate  with  aSprengel's  mercurial  air-pump, 
and,  after  heating  the  chlorate  to  fusion,  to  produce  a  vacuum  in 
the  apparatus.  The  chlorate  may  be  again  heated  until  oxygen 
begins  to  pass  through  the  mercury  at  the  end  of  the  Sprengel,  the 
heat  then  withdrawn,  and  a  vacuum  again  obtained.  The  chlorate 
is  once  more  heated,  and  the  oxygen  collected  at  the  bottom  of 
the  Sprengel.  Of  course  the  usual  precautions  for  obtaining  an 
air- tight  joint  between  the  bulb  and  the  Sprengel  must  be  taken, 
such  as  surrounding  the  caoutchouc  connector  with  a  tube  filled 
with  mercury. 

The  hydrogen  for  these 
experiments  must  be  pre- 
pared by  electrolysis,  since 
that  from  other  sources  is 
liable  to  contamination  with 
impurities  which  would 
vitiate  the  analysis.  The 
apparatus  employed  by 
Bun  sen  for  this  purpose 
(fig.  80)  consists  of  a  glass 
tube,  closed  at  the  lower 
end,  and  with  a  funnel  at 
the  other,  into  which  a  de- 
livery tube  is  ground,  the 
funnel  acting  as  a  water- 
joint.  A  platinum  wire  is 
sealed  into  the  lower  part  of 
the  tube ;  and  near  the 
upper  end  another  wire, 
with  a  platinum  plate  at- 
tached, is  fused  into  the 
glass.  Some  amalgam  of 
zinc  is  placed  into  the  tube 
so  .  as  to  cover  the  lower 
platinum  wire,  and  the  ap- 
paratus filled  nearly  to  the  neck  with  water,  acidulated  with 
sulphuric  acid.  On  connecting  the  platinum  wires  with  a  battery 
of  two  or  three  cells,  the  iipper  wire  being  made  the  negative 
electrode,  pure  hydrogen  is  evolved  from  the  platinum  plate,  and, 
after  the  expulsion  of  the  air,  may  be  at  once  passed  into  the 
eudiometer,  or,  if  preferred,  collected  in  tubes  for  future  use. 
Unfortunately,  in  this  form  of  apparatus,  the  zinc  amalgam  soon 
becomes  covered  with  a  saturated  solution  of  zinc  sulphate,  which 
puts  a  stop  to  the  electrolysis.  In  order  to  remove  this  layer, 


Pig.  80. 


476 


VOLUMETRIC   ANALYSIS. 


§  97. 


Buns  en  has  a  tube  fused  into  the  apparatus  at  the  surface  of  the 
amalgam;  this  is  bent  upwards  parallel  to  the  larger  tube,  and 
curved  downwards  just  below  the  level  of  the  funnel.  The  end 
of  the  tube  is  closed  with  a  caoutchouc  stopper.  On  removing  the 
stopper,  and  pouring  fresh  acid  into  the  funnel,  the  saturated  liquid 
is  expelled. 

Another  form  of  apparatus  for  preparing  electrolytic  hydrogen 
may  readily  be  constructed.  A  six-ounce  wide-mouth  bottle  is 
fitted  with  a  good  cork,  or  better,  with  a  caoutchouc  stopper.  In 
the  stopper  four  tubes  are  fitted  (fig.  81).  The  first  is  a  delivery 
tube,  provided  with  a  U-tube,  containing  broken  glass  and  sulphuric 
acid,  to  conduct  the  hydrogen  to  the  mercurial  trough.  The  second 
tube,  about  5  centimeters  long,  and  filled  with  mercury,  has  fused 
into  its  lower  end  a  piece  of  platinum  wire  carrying  a  strip  of 

foil,  or  the  wire  may  be 
simply  flattened.  The  third 
tube  passes  nearly  to  the 
bottom  of  the  bottle,  the 
portion  above  the  cork  is 
bent  twice  at  right  angles, 
and  cut  off",  so  that  the 
open  end  is  a  little  above 
the  level  of  the  shoulder 
of  the  bottle ;  a  piece  of 
caoutchouc  tube,  closed  by 
a  compression  cock,  is  fitted 
to  the  end  of  the  tube. 
The  fourth  tube  is  a  piece 
of  combustion  tube  about 
30  centimeters  in  length, 
and  which  may  with  ad- 
vantage be  formed  into  a 
funnel  at  the  top.  This 
tube  reaches  about  one-third 
down  the  bottle,  and  inside 
it  is  placed  a  narrower  glass 
tube,  attached  at  its  lower 
end  by  a  piece  of  caoutchouc 
connector  to  a  rod  of  amalgamated  zinc.  The  tube  is  filled  with 
mercury  to  enable  the  operator  readily  to  connect  the  zinc  with 
the  battery ;  some  zinc  amalgam  is  placed  at  the  bottom  of  the 
bottle ;  and  dilute  sulphuric  acid  is  poured  in  through  the  wide 
tube  until  the  bottle  is  nearly  filled  with  liquid.  To  use  the 
apparatus,  the  delivery  tube  is  dipped  into  mercury,  the  wire  from 
the  positive  pole  of  the  battery  placed  into  the  mercury  in  the 
tube  to  which  the  zinc  is  attached,  and  the  negative  pole  connected 
by  means  of  mercury  with  the  platinum  plate.  The  current, 
instead  of  passing  between  the  amalgam  at  the  bottom  of  the 


Tig.  81. 


§  97. 


EXPLOSION   OF   GASES. 


477 


vessel  and  the  platinum  plate,  as  in  Bunsen's  apparatus,  travels 
from  the  rod  of  amalgamated  zinc  to  the  platinum,  consequently 
the  current  continues  to  pass  until  nearly  the  whole  of  the  liquid 
in  the  bottle  has  become  saturated  with  zinc  sulphate.  As  soon  as 
the  hydrogen  is  evolved,  of  course  a  column  of  acid  is  raised  in 
the  funnel  until  the  pressure  is  sufficient  to  force  the  gas  through 
the-  mercury  in  which  the  delivery  tube  is  placed.  Care  must  be 
taken  that  the  quantity  of  acid  in  the  bottle  is  sufficient  to  prevent 
escape  of  gas  through  the  funnel  tube,  and  also  that  the  delivery 
tube  does  not  pass  too  deeply  into  the  mercury  so  as  to  cause  the 
overflow  of  the  acid.  When  the  acid  is  exhausted,  the  compression 
cock  on  the  bent  tube  is  opened  and  fresh  acid  poured  into  the 
funnel;  the  dense  zinc  sulphate  solution  is  thus  replaced  by  the 
lighter  liquid,  and  the  apparatus  is  again  ready  for  use. 

A  very  convenient  apparatus  for  transferring  oxygen  and 
hydrogen  into  eudiometers  is  a  gas  pipette,  figured  and  described 
(fig.  53,  page  398). 

It  is  necessary  in  all  cases  to  add  an  excess  of  the  oxygen  or 
hydrogen  before  exploding,  and  it  is  well  to  be  able  to  measure 
approximately  the  amount  added  without  going  through  the  whole 
of  the  calculations.  This  may  be  conveniently  done  by  making  a 
rough  calibration  of  the  eudiometer  in  the  following  manner : — 
The  tube  is  filled  with  mercury,  a  volume  of  air  introduced  into 
it  from  a  small  tube,  and  the  amount  of  the  depression  of  the 
mercury  noted ;  a  second  volume  is  now  passed  up,  a  further 
depression  will  be  produced,  but  less  in  extent  than  the  previous 
one,  in  consequence  of  the  shorter  column  of  mercury  in  the  tube. 
This  is  repeated  until  the  eudiometer  is  filled,  and  by  means  of  a 
table  constructed  from  these  observations,  but  without  taking  any 
notice  of  the  variations  of  thermometer  or  barometer,  the  operator 
can  introduce  the  requisite  quantity  of  gas.  It  may  be  convenient 
to  make  this  calibration  when  the  eudiometer  is  inclined  in  the 
support,  and  also  when  placed  perpendicularly,  so  that  the  gas 
may  be  introduced  when  the  tube  is  in  either  position.  A  table 
like  the  following  is  thus  obtained : — 


DIVISIONS. 

Measures. 
1 

Tube 
Inclined. 

27 

Tube 
Perpendicular. 

45 

2 

45 

69 

3 

61 

87 

4 

75 

102 

5 

88 

116 

6 

100 

128 

7 

109 

138 

&c. 

&c. 

&c. 

In  explosions  of  hydrocarbons  with  oxygen,  it  is  necessary  to 


478  VOLUMETRIC  ANALYSIS.  §    97. 

have  a  considerable  excess  of  the  latter  gas  in  order  to  moderate 
the  violence  of  the  explosion.  The  same  object  may  be  attained 
by  diluting  the  gas  with  atmospheric  air,  but  it  is  found  that 
sufficient  oxygen  serves  equally  well.  If  the  gas  contains  nitrogen, 
it  is  necessary  subsequently  to  explode  the  residual  gas  with 
hydrogen;  and  if  oxygen  only  has  been  used  for  diluting  the 
gas,  a  very  large  quantity  of  hydrogen  must  be  added,  which 
may  augment  the  volume  in  the  eudiometer  to  an  inconvenient 
extent.  When  atmospheric  air  has  been  employed,  this  incon- 
venience is  avoided.  After  the  introduction  of  the  oxygen,  the 
eudiometer  is  restored  to  its  vertical  position,  allowed  to  stand 
for  an  hour,  and  the  volume  read  off. 

The  determination  of  the  quantity  of  oxygen  which  must  be 
added  to  combustible  gases  so  as  to  prevent  the  explosion  from  being 
too  violent,  and  at  the  same  time  to  ensure  complete  combustion, 
has  been  made  the  subject  of  experiment.  When  the  gases 
before  explosion  are  under  a  pressure  equal  to  about  half  that 
of  the  atmosphere,  the  following  proportions  of  the  gases  must 
be  employed : — 

Volume  of          Volume  of 
Combustible  Gas.       Oxygen. 

Hydrogen      ....  1  1"5 

Carbonic  oxide       ...  1  1'5 

Marsh  gas      ....  1  5 

Gases  containing  two  atoms  of 

carbon  in  the  molecule,  as 

Methyl,  C2IP  ...  1  10 

Gases  containing  three  atoms  of 

carbon  in  the  molecule,  as 

Propylic  hydride,  C3H8  .1  18 

Gases  containing  four  atoms  of 

carbon  in  the  molecule,  as 

Ethyl,  C4H10      ...  1  25 

In  cases  of  mixtures  of  two  or  more  combustible  gases, 
proportionate  quantities  of  oxygen  must  be  introduced. 

At  the  time  of  the  explosion,  it  is  necessary  that  the 
eudiometer  should  be  carefully  closed  to  prevent  the  loss 
of  gas  by  the  sudden  expansion.  For  this  purpose  a 
thick  plate  of  caoutchouc,  three  or  four  centimeters  wide,  is 
cemented  on  a  piece  of  cork  by  means  of  marine  glue,  or  some 
similar  substance,  and  the  lower  surface  of  the  cork  cut  so  as  to  lie 
firmly  at  the  bottom  of  the  mercurial  trough  (fig.  82).  It  is,  how- 
ever, preferable  to  have  the  caoutchouc  firmly  fixed  in  the  trough. 
As  the  mercury  does  not  adhere  to  the  caoutchouc,  there  is 
some  risk  of  air  entering  the  eudiometer  after  the  explosion ; 
this  is  obviated  by  rubbing  the  plate  with  some  solution  of 
corrosive  sublimate  before  introducing  it  into  the  mercury,  which 


97. 


EXPLOSION  OF  GASES. 


479 


causes  the  metal  to  wet  the  caoutchouc  and  removes  all  air  from 
its  surface.  When  the  caoutchouc  is  not  fixed  in  the  trough,  the 
treatment  with  the  corrosive  sublimate  has  to  be  repeated  before 
every  experiment,  and  this  soils  the  surface  of  the  mercury  to  an 
inconvenient  extent.  The  cushion  is  next  depressed  to  the  bottom 
of  the  trough,  and  the  eudiometer  placed  on  it  and  firmly  held 
down  (fig.  83).  If  this  is  done  with  the  hands,  the  tube  must 
be  held  by  that  portion  containing  the  mercury,  for  it  is  found 
that  when  eudiometers  burst  (which,  however,  only  happens  when 
some  precaution  has  been  neglected) 
they  invariably  give  way  just  at  the 
level  of  the  mercury  within  -the  tube, 
and  serious  accidents  might  occur  if 
the  hands  were  at  this  point.  The 
cause  of  the  fracture  at  this  point  is 
the  following : — Though  the  gas  is  at 
a  pressure  below  that  of  the  atmosphere 
before  the  explosion,  yet  at  the  instant 
of  the  passage  of  the  spark,  the  ex- 
pansion of  the  gas  at  the  top  of  the 
tube  condenses  the  layer  just  below  it ; 
this  on  exploding  increases  the  density 
of  the  gas  further  down  the  tube,  and 
by  the  time  the  ignition  is  communicated 
to  the  lowest  quantity  of  gas,  it  may 
be  at  a  pressure  far  above  that  of  the 
atmosphere.  It  may  be  thought  that 
the  explosion  is  so  instantaneous  that 
this  explanation  is  merely  theoretical; 
but  on  exploding  a  long  column  of  gas,  the 
time  required  for  the  complete  ignition 
is  quite  perceptible,  and  sometimes  the 
flash  may  be  observed  to  be  more 
brilliant  at  the  surface  of  the  mercury. 
Some  experimenters  prefer  to  fix  the 
eudiometer  by  means  of  an  arm  from 
a  vertical  stand,  the  arm  being  hollowed 
out  on  the  under  side,  and  the  cavity 
lined  with  cork. 

If  a  large  quantity  of  incombustible 
gas   is   present,  the   inflammability  of 


Fig.  83. 


the  mixture  may  be  so  much  reduced  that  either  the  explosion 
does  not  take  place  at  all,  or,  what  may  be  worse,  only  a  partial 
combustion  ensues.  To  obviate  this,  some  explosive  mixture  of 
oxygen  and  hydrogen,  obtained  by  the  electrolysis  of  water, 
must  be  introduced.  The  apparatus  used  by  Buns  en  for  this 
purpose  is  shown  in  fig.  84.  The  tube  in  which  the  electrolysis 
takes  place  is  surrounded  by  a  cylinder  containing  alcohol,  in  order 


480 


VOLUMETRIC   ANALYSIS. 


to  prevent  the  heating  of  the  liquid.  A  convenient  apparatus 
for  the  preparation  of  this  gas  is  made  by  blowing  a  bulb  of 
about  four  centimeters  in  diameter  on  the  end  of  a  piece  of  narrow 
glass  tube,  sealing  two  pieces  of  flattened  platinum  wire  into 
opposite  sides  of  the  globe,  and  bending  the  tube  so  as  to  form 
a  delivery  tube.  Dilute  sulphuric  acid,  containing  about  one  volume 
of  acid  to  twenty  of  water,  is  introduced  into  the  globe,  either 
before  bending  the  tube,  by  means  of  a  funnel  with  a  fine  long 
stem,  or,  after  the  bending,  by  warming  the  apparatus,  and 

plunging  the  tube  into 
the  acid.  Care  must  be 
taken  that  the  acid  is 
dilute,  and  that  the 
battery  is  not  too  strong, 
in  order  to  avoid  the 
formation  of  ozone,  which 
would  attack  the  mer- 
cury, causing  the  sides 
of  the  eudiometer  to  be 
soiled,  at  the  same  time 
producing  a  gas  too  rich 
in  hydrogen. 

The  spark  necessary 
to  effect  the  explosion 
may  be  obtained  from 
several  sources.  An  ordi- 
nary electrical  machine 
or  electrophorus  may  be 
used,  but  these  are  liable 
to  get  out  of  order  by 
damp.  Bun  sen  uses  a 
porcelain  tube,  which  is 
rubbed  with  a  silk  rub- 
ber, coated  with  electrical 
amalgam ;  by  means  of 

Fig.  84.  this  a  small  Leyden  jar 

is  charged.     A  still  more 

convenient  apparatus  is  an  induction  coil  large  enough  to  produce 
a  spark  of  half  an  inch  in  length. 

After  the  explosion  the  eudiometer  is  slightly  raised  from  the 
caoutchouc  plate  to  allow  the  entrance  of  mercury.  When  no  more 
mercury  rushes  in,  the  tube  is  removed  from  the  caoutchouc  plate, 
placed  in  a  perpendicular  position,  and  allowed  to  remain  for  at 
least  an  hour  before  reading.  After  measuring  the  contraction,  it  is 
generally  necessary  to  absorb  the  carbonic  anhydride  formed  by  the 
combustion  by  means  of  a  potash  ball,  in  the  way  previously 
described.  In  some  rare  instances  the  amount  of  water  produced 
in  the  explosion  with  oxygen  must  be  measured.  If  this  has  to  be 


§  97. 


METHODS   OF  CALCULATION. 


481 


done,  the  eudiometer,  the  mercury,  th,e  original  gas,  and  the  oxygen 
must  all  be  carefully  dried.  After  the  explosion  the  eudiometer 
is  transferred  to  a  circular  glass  vessel  containing  mercury,  and 
attached  to  an  iron- wire  support,  by  which  the  entire  arrangement 
can  be  suspended  in  a  glass  tube  adapted  to  the  top  of  an  iron 
boiler,  from  which  a  rapid  current  of  steam  may  be  passed  through 
the  glass  tube,  so  as  to  heat  the  eudiometer  and  mercury  to  an 
uniform  temperature  of  100°.  From  the  measurements  obtained  at 
this  temperature  the  amount  of  water  produced  may  be  calculated. 
If  three  combustible  gases  are  present,  the  only  data  required  for 
calculation  are,  the  original  volume  of  the  gas,  the  contraction  on 
explosion,  and  the  amount  of  carbonic  anhydride  generated.  When 
the  original  gas  contains  nitrogen,  the  residue  after  explosion  with 
excess  of  oxygen  consists  of  a  mixture  of  oxygen  and  nitrogen.  To 
this  an  excess  of  hydrogen  is  added,  and  the  mixture  exploded;  the 
contraction  thus  produced  divided  by  3  gives  the  amount  of  oxygen 
in  the  residual  gas,  and  the  nitrogen  is  found  by  difference. 

It  is  obvious  that,  by  subtracting  the  quantity  of  residual  oxygen, 
thus  determined  by  explosion  with  hydrogen,  from  the  amount 
added,  in  the  first  instance,  to  the  combustible  gas,  the  volume  of 
oxygen  consumed  in  the  explosion  may  be  obtained.  Some  chemists 
prefer  to  employ  this  number  instead  of  the  contraction  as  one  of 
the  data  for  the  calculation. 

"We  must  now  glance  at  the  mode  of  calculation  to  be  employed 
for  obtaining  the  percentage  composition  of  a  gas  from  the  numbers 
arrived  at  by  the  experimental  observations. 

The  following  table  shows  the  relations  existing  between  the 
volume  of  the  more  important  combustible  gases  and  the  products 
of  the  explosion  : — 


Name  of  Gas. 

Volume  of 
Combustible 
Gas. 

Volume  of 
Oxygen 
Consumed. 

Contraction 
after 
Explosion. 

Hi! 

Hi! 

Hydrogen,  H 

1 

0-5 

1-5 

0 

Carbonic  Oxide,  CO 

1 

0-5 

0-5 

1 

Methylic  Hydride,  CH3H       . 

1 

2 

2 

1 

Acetylene,  C2H2    . 

1 

2-5 

1-5 

2 

Olefiant  Gas,  C2H* 

1 

3 

2 

2 

Methyl,  CH3,  CH3 

1 

3-5 

2-5 

2 

Ethylic  Hydride,  C2H5H 

1 

3-5 

2-5 

2 

Propvlene,  C3H6    . 

1 

4-5 

2-5 

3 

Propylic  Hydride,  C3H7H       . 

1 

5 

3 

3 

Butylene,  C4H8      .         . 

1 

6 

3 

4 

Ethyl,  C2H5,  C2H5 

1 

6-5 

3-5 

4 

Butylic  Hydride,  C4H9H 

1 

6-5 

3-5 

4 

I  I 


482  VOLUMETRIC  ANALYSIS.  §    97. 

As  an  example,  we  may  take  a  mixture  of  hydrogen,  carbonic 
oxide,  and  marsh  gas,  which  gases  may  be  designated  by  x,  ?/,  and  z 
respectively.  The  original  volume  of  gas  may  be  represented  by  A, 
the  contraction  by  C,  and  the  amount  of  carbonic  anhydride  by  D. 

A  will,  of  course,  be  made  up  of  the  three  components,  or 

A  =  x  +  y  +  z. 

C  will  be  composed  as  follows  :  —  When  a  mixture  of  hydrogen  and 
oxygen  is  exploded,  the  gas  entirely  disappears.  One  volume  of 
hydrogen  combining  with  half  a  volume  of  oxygen,  the  contraction 
will  be  1J  times  the  quantity  of  hydrogen  present,  or  1  \x.  In  the 
case  of  carbonic  oxide,  1  volume  of  this  gas  uniting  with  half  its 
volume  of  oxygen  produces  1  volume  of  carbonic  anhydride,  so 
the  contraction  due  to  the  carbonic  oxide  will  be  half  its  volume, 
or  \y.  Lastly,  1  volume  of  marsh  gas  combining  with  2  volumes  of 
oxygen  generates  1  volume  of  carbonic  anhydride,  so  the  contraction 
in  this  case  will  be  twice  its  volume,  or  2z.  Thus  we  have  — 


Since  carbonic  oxide  on  combustion  forms  its  own  volume  of 
carbonic  anhydride,  the  amount  produced  by  the  quantity  present 
in  the  mixture  will  be  y.  Marsh  gas  also  generates  its  own  volume 
of  carbonic  anhydride,  so  the  quantity  corresponding  to  the  marsh 
gas  in  the  mixture  will  be  z.  Therefore 


It  now  remains  to  calculate  the  values  of  x,  y,  and  z  from  the 
experimental  numbers  A,  C,  and  D,  which  is  done  by  the  help 
of  the  following  equations  :  — 


To  find    -  =  A, 


For  y  we  have- 


=  4D  -  2C  , 
3x  _  =  3A-3D, 

3y         =  3A-2C  +  D,     or 
3A-2C  +  D 


The  value  of  z  is  thus  found — 


_     3A-2C  +  D 

D-       -g ,     or 

2C-3A  +  2D 
*= ' 


§    97.  METHODS   OF  CALCULATION.  483 

By  replacing  the  letters  A,  C,  and  D  by  the  numbers  obtained 
by  experiment,  the  quantities  of  the  three  constituents  in  the 
volume  A  may  easily  be  calculated  by  the  three  formulae : — 

x  =  A  -  D  =  hydrogen  , 

3A-2C  +  D 

y  = o =  carbonic  oxide  , 

2C-3A  +  2D 

z  = — o =  marsh  gas  . 


The  percentage  composition  is,  of  course,  obtained  by  the  simple 
proportions  — 

A  :  x  :  :  100  :  per-cent.  of  hydrogen  , 

A  :  y  :  :  100  :  per-cent.  of  carbonic  oxide  , 

A  :  z  :  :  100  :  per-cent.  of  marsh  gas  . 

If  the  gas  had  contained  nitrogen,  it  would  have  been  determined 
by  exploding  the  residual  gas,  after  the  removal  of  the  carbonic 
anhydride,  with  excess  of  hydrogen.  The  contraction  observed, 
divided  by  3,  would  give  the  volume  of  oxygen  in  the  residue,  and 
this,  deducted  from  the  residue,  would  give  the  amount  of  nitrogen. 
If  A  again  represents  the  original  gas,  and  n  the  amount  of  nitrogen 
it  contains,  the  expression  A  -  n  would  have  to  be  substituted  for 
A  in  the  above  equations. 

It  may  be  as  well  to  develop  the  formula  for  obtaining  the  same 
results  by  observing  the  volume  of  oxygen  consumed  instead  of  the 
contraction.  If  B  represent  the  quantity  of  oxygen,  we  shall  have 

B  = 

the  values  of  A  and  D  remaining  as  before,  x  =  A  -  D. 
z  is  thus  found  — 

^  2B, 


3z  —  2B  -  A  ,     or 
2B-A 


For  y  — 

D  =  ?/  +  z 

y  =  D-Z  = 

2B~A 


3—  ,     or 


3D-2B  +  A 


484  VOLUMETRIC  ANALYSIS.  §    97. 

Thus  we  have — 

x  =  A-V 

3D-2B  +  A 

y= 3- 

2B-A 


Having  thus  shown  the  mode  of  calculation  of  the  forniulse,  it- 
will  be  well  to  give  some  examples  of  the  formulae  employed  in 
some  of  the  cases  which  most  frequently  present  themselves  in  gas- 
analysis.  In  all  cases  — 

A  =  original  mixture  , 

C  =  contraction  , 

D  =  carbonic  anhydride  produced. 

1.      Hydrogen   and   Nitrogen. 


Excess  of  oxygen  is  added,  and  the  contraction  on  explosion 
observed  :  — 

_2C 

X  -       q       J 

3A-2C 

y  =     —  -  ,  or  A  -  x  . 


2.      Carbonic    Oxide   and   Nitroen. 


The  gas  is  exploded  with  excess  of  oxygen,  and  the  amount  of 
carbonic  anhydride  produced  is  estimated  :  — 


3.      Hydrogen,    Carbonic    Oxide,    and   Nitrogen. 

H  =  »;  C0  =  y;  N  =  z. 

In  this   case   the   contraction   and    the   quantity   of    carbonic 
anhydride  are  measured  :  — 

2C-D 


_3A-2C-2D 


§    97.  METHODS  OF  CALCULATION.  485 

4.      Hydrogen,   Marsh   Gas,   and  Nitrogen. 


=  y,       =  z. 

2C-4P 

~3        ' 

y  =  B, 

3A-2C  +  D 
3 

o.      Carbonic   Oxide,   Marsh   Gas,   and   Nitrogen 


4P-2C 

3        ' 
2C-D 


6.      Hydrogen,   Methyl  (or   Ethylic   Hydride),   and 
Nitrogen. 


2  = 


4C-5D 

6       '  HUBERT 

D 

3A-2C  +  D 


7.      Carbonic   Oxide,   Methyl   (or   Ethylic   Hydride), 
and   Nitrogen. 


C0=x; 

5D-4C 


2C-D 

y=  -- 


3A-4D  +  2C 


486  VOLUMETKIC  ANALYSIS.  §    9*7. 

8.      Hydrogen,    Carbonic   Oxide,    and   Marsh   Gas. 
TL  =  x;  C0=y;  CH4  =  2. 


3A-2C  +  P 

y  =      —3        » 

2C-3A  +  2D 

~~    " 


9.      Hydrogen,    Carbonic    Oxide,    and    Ethylic    Hydride 
(or   Methyl). 


3A  +  2C-4D 

•-  --  6  --  > 
3A-2C  +  D 

y  =      —3  —  > 

2C-3A  +  2D 
i.         -g  --  . 

10.      Carbonic  Oxide,  Marsh   Gas,  and  Ethylic  Hydride 
(or   Methyl). 


3A-2C  +  D 
x=        —  g—    -, 

3A  +  2C-4D 


11.      Hydrogen,    Marsh   Gas,    and   Acetylene. 

TL  =  x',  CH*  =  y;  C2H2-=^. 

5A-2C-D 
^^  --  2  --  ' 
?/  =  2C-3A, 
D-2C  +  3A 

"T"      ' 

12.      Hydrogen,    Marsh   Gas,    and   Ethylic   Hydride 
(or   Methyl). 


This  mixture  cannot  be  analyzed  by  indirect  determination,  since 
a  mixture  of  two  volumes  of  hydrogen  with  two  volumes  of  ethylic 


§    97.  METHODS   OF  CALCULATION.  487 

hydride  (or  methyl)  has  the  same  composition  as  four  volumes  of 
marsh  gas  — 


and,  consequently,  would  give  rise  to  the  same  products  on 
combustion  with  oxygen  as  pure  marsh  gas  — 

C2H6  +  H2  +  O8  =  2C02  +  40H2  ; 

2CH4  +  O8  =  2C02  +  40H2. 

In  this  case  it  is  necessary  to  estimate  by  direct  determination  the 
ethylic  hydride  (or  methyl)  in  a  separate  portion  of  the  gas  by 
absorption  with  alcohol,  another  quantity  of  the  mixture  being 
exploded  with  oxygen,  and  the  amount  of  carbonic  anhydride  pro- 
duced and  measured.  If  the  quantity  absorbed  by  alcohol  =  E,  then 


13.      Hydrogen,    Carbonic   Oxide,    Propylic   Hydride. 
TL  =  x',  C0  =  y;  C3H8  =  z. 
3A  +  4C-5D 


X= 


9 
3A-2G  +  P 

U  Q  5 

2C-3A  +  2D 
z=         -5 . 

14.     Carbonic  Oxide,  Marsh  Gas,  and  Propylic  Hydride. 

3A-2C  +  P 
3A  +  4C-5D 

y  = g—    -5 

D-A 


15.      Carbonic    Oxide,    Ethylic   Hydride   (or   Methyl), 
and   Propylic   Hydride. 


3A-2C  +  P 
x-  3  , 

3A  +  4C-5D 

y=      -3-    - 

4D-3A-2C 

2=  -  *  - 


488  VOLUMETEIC  ANALYSIS.  §    97. 

16.      Marsh   Gas,    Ethylic   Hydride   (or    Methyl),    and 
Propylic   Hydride. 

?/    C3H8  =  z. 


As  a  mixture  of  two  volumes  of  marsh  gas  and  two  of  propylic 
hydride  has  the  same  composition  as  four  of  ethylic  hydride  (or 
methyl)  — 

—  2C2H6, 


the  volume  absorbed  by  alcohol,  and  which  consists  of  ethylic 
hydride  (or  methyl)  and  propylic  hydride,  must  be  determined, 
and  another  portion  of  the  gas  exploded,  and  the  contraction 
measured.  If  E  represents  the  volume  absorbed  — 


17.      Hydrogen,  Carbonic  Oxide,  and  Ethyl  (or  Eutylic 

Hydride). 


A  +  2C-2D 

x  —  4  j 

3A-2C  +  D 

y  =  --  3-  -, 

2C  +  2D-3A 

"H" 


18.      Nitrogen,    Hydrogen,    Carbonic   Oxide,    Ethylic 
Hydride   (or   Methyl),   and   Butylic   Hydride  (or  Ethyl). 


In  one  portion  of  the  gas  the  ethylic  hydride  (or  methyl)  and 
the  butylic  hydride  (or  ethyl)  are  absorbed  by  alcohol  ;  the  amount 
absorbed  =  E. 

A  second  portion  of  the  original  gas  is  mixed  with  oxygen  and 
exploded,  the  amount  of  contraction  and  of  carbonic  anhydride 
being  measured. 

The  residue  now  contains  the  nitrogen  and  the  excess  of  oxygen  ; 
to  this  an  excess  of  hydrogen  is  added,  the  mixture  exploded,  and 
the  contraction  measured.  From  this  the  quantity  of  nitrogen  is 
thus  obtained.  Let  — 

G  =  excess  of  oxygen  and  nitrogen, 

v  =  excess  of  oxygen, 

n  =  nitrogen, 
C'  =  contraction  on  explosion  with  hydrogen. 


98.  IMPROVED  GAS  APPARATUS.  489 

Then— 


a 

v  = 


•       =   • 

3G-C' 
3 

From    these    data    the    composition    of    the    mixture    can    be 
determined  — 

2C-D-3E 
w=    "a  --  ' 
_3A-2C  +  P—  3rc 


2C—  3A  +  2D— 


6 

MODIFICATIONS    AND    IMPROVEMENTS    UPON    THE 
FOREGOING    PROCESSES. 

§  98.  IN  the  method  of  gas  analysis  that  we  have  been  consider- 
ing, the  calculations  of  results  are  somewhat  lengthy,  as  will  be 
seen  by  a  reference  to  the  example  given  of  the  analysis  of  a 
mixture  of  air  and  carbonic  anhydride  (page  469).  Besides  this,  the 
operations  must  be  conducted  in  a  room  of  uniform  temperature, 
and  considerable  time  allowed  to  elapse  between  the  manipulation 
and  the  readings  in  order  to  allow  the  eudiometers  to  acquire  the 
temperature  of  the  surrounding  air ;  and,  lastly,  the  absorption  of 
gases  by  solid  reagents  is  slow.  These  disadvantages  are  to  a 
great  extent  counterbalanced  by  the  simplicity  of  the  apparatus, 
and  of  the  manipulation. 

From  time  to  time  various  chemists  have  proposed  methods  by 
which  the  operations  are  much  hastened  and  facilitated,  and  the 
calculations  shortened.  It  will  be  necessary  to  mention  a  few  of 
these  processes,  which,  however,  require  special  forms  of  apparatus. 

Williamson  and  Russell  have  described  (Proceedings  of  the 
Royal  Society,  ix.  218)  an  apparatus,  by  means  of  which  the 
gases  in  the  eudiometers  are  measured  under  a  constant  pressure, 
the  correction  for  temperature  being  eliminated  by  varying  the 
column  of  mercury  in  the  tube  so  as  to  compensate  for  the  alteration 
of  volume  observed  in  a  tube  containing  a  standard  volume  of  moist 
air.  In  this  case  solid  reagents  were  employed  in  the  eudiometers. 


490  VOLUMETEIC   ANALYSIS.  §    98. 

In  1864  they  published  (/.  C.  S.  xvii.  238)  a  further  develop- 
ment of  this  method,  in  which  the  absorptions  were  conducted  in 
a  separate  laboratory  vessel,  by  which  means  the  reagents  could  be 
employed  in  a  pasty  condition  and  extended  over  a  large  surface. 

And  in  1868  Eussell  improved  the  apparatus,  so  that  liquid 
reagents  could  be  used  in  the  eudiometers,  and  the  analysis  rapidly 
executed.  A  description  of  this  last  form  of  instrument  may  be 
found  in  /.  O.  S.  xxi.  128. 

The  gutta-percha  mercury  trough  employed  is  provided  with 
a  deep  well,  into  which  the  eudiometer  can  be  depressed  to  any 
required  extent,  and  on  the  surface  of  the  mercury  a  wide  glass 
cylinder,  open  at  both  ends  and  filled  with  water,  is  placed.  The 
eudiometer  containing  the  gas  to  be  examined  is  suspended  Avithin 
the  cylinder  of  water  by  means  of  a  steel  rod  passing  through 
a  socket  attached  to  a  stout  standard  firmly  fixed  to  the  table.  In 
a  similar  manner,  a  tube  containing  moist  air  is  placed  by  the  side 
of  the  eudiometer.  The  clamp  supporting  this  latter  tube  is 
provided  with  two  horizontal  plates  of  steel,  at  which  the  column 
of  the  mercury  is  read  off.  When  a  volume  of  gas  has  to  be 
measured,  the  pressure  tube  containing  the  moist  air  is  raised  or 
lowered,  by  means  of  an  ingeniously  contrived  fine  adjustment, 
until  the  mercury  stands  very  nearly  at  the  level  of  one  of  the 
horizontal  steel  plates.  The  eudiometer  is  next  raised  or  lowered 
until  the  column  of  mercury  within  it  is  at  the  same  level.  The 
final  adjustment  to  bring  the  top  of  the  meniscus  exactly  to  the 
lower  edge  of  the  steel  bar  is  effected  by  sliding  a  closed  wide  glass 
tube  into  the  mercury  trough.  Thus  we  have  two  volumes  of  gas 
under  the  same  pressure  and  temperature,  and  both  saturated  with 
moisture.  If  the  temperature  of  the  water  in  the  cylinder  increased, 
there  would  be  a  depression  of  the  columns  in  both  tubes ;  but  by 
lowering  the  tubes,  and  thus  increasing  the  pressure  until  the 
volume  of  air  in  the  pressure  tube  was  the  same  as  before,  it  would 
be  found  that  the  gas  in  the  eudiometer  was  restored  to  the  original 
volume.  Again,  if  the  barometric  pressure  increased,  the  volumes 
of  the  gases  would  be  diminished ;  but,  by  raising  the  tubes  to  the 
necessary  extent,  the  previous  volumes  would  be  obtained.  There- 
fore, in  an  analysis,  it  is  only  necessary  to  measure  the  gas  at 
a  pressure  equal  to  that  which  is  required  to  maintain  the  volume 
of  moist  air  in  the  pressure  tube  constant.  The  reagents  are 
introduced  into  the  eudiometer  in  the  liquid  state  by  means  of 
a  small  syringe  made  of  a  piece  of  glass  tube  about  one-eighth  of 
an  inch  in  diameter.  For  this  purpose  the  eudiometer  is  raised 
until  its  open  end  is  just  below  the  surface  of  the  mercury,  and 
the  syringe,  which  is  curved  upwards  at  the  point,  is  depressed  in 
the  trough,  passed  below  the  edge  of  the  water-cylinder,  and  the 
extremity  of  the  syringe  introduced  into  the  eudiometer.  When 
a  sufficient  quantity  of  the  liquid  has  been  injected,  the  eudiometer 
is  lowered  and  again  raised,  so  as  to  moisten  the  sides  of  the  tube 


§  98.        KUSSELL'S  GAS  ArpAKATUs.         491 

Avith  the  liquid,  and  thus  hasten  the  absorption.  Ten  minutes  was 
found  to  be  a  sufficient  time  for  the  absorption  of  carbonic 
anhydride  when  mixed  with  air. 

To  remove  the  liquid  reagent,  a  ball  of  moistened  cotton  wool  is 
employed.  The  ball  is  made  in  the  following  manner : — A  piece 
of  steel  wire  is  bent  into  a  loop  at  one  end,  and  some  cotton  wool 
tightly  wrapped  round  it.  It  is  then  dipped  in  water  and  squeezed 
with  the  hand  under  the  liquid  until  the  air  is  removed.  The  end 
of  the  steel  wire  is  next  passed  through  a  piece  of  glass  tube, 
curved  near  one  end,  and  the  cotton  ball  drawn  against  the  curved 
extremity  of  the  tube.  The  ball,  saturated  with  water,  is  now 
depressed  in  the  mercury  trough,  and,  after  as  much  of  the  water 
as  possible  has  been  squeezed  out  of  it,  it  is  passed  below  the 
eudiometer,  and,  by  pushing  the  wire,  the  ball  is  brought  to  the 
surface  of  the  mercury  in  the  eudiometer  and  rapidly  absorbs  all 
the  liquid  reagent,  leaving  the  meniscus  clean.  The  ball  is  removed 
with  a  slight  jerk,  and  gas  is  thus  prevented  from  adhering  to  it. 
It  is  found  that  this  mode  of  removing  the  liquid  can  be  used 
without  fear  of  altering  the  volume  of  the  gas  in  the  eudiometer. 

Carbonic  anhydride  may  be  absorbed  by  a  solution  of  potassic 
hydrate,  and  oxygen  by  means  of  potassic  hydrate  and  pyrogallic 
acid.  The  determination  of  ethylene  is  best  effected  by  means  of 
fuming  sulphuric  acid  on  a  coke  ball,  water  and  dilute  potassic 
hydrate  being  subsequently  introduced  and  removed  by  the  ball  of 
cotton  wool. 

Doubtless  this  mode  of  using  the  liquid  reagents  might  be 
employed  with  advantage  in  the  ordinary  process  of  analysis  to 
diminish  the  time  necessary  for  the  absorption  of  the  gases.  By 
this  process  of  Eussell's  the  calculations  are  much  shortened 
and  facilitated,  the  volumes  read  off  being  comparable  among 
themselves ;  this  will  be  seen  by  an  example,  taken  from  the 
original  memoir,  of  the  determination  of  oxygen  in  air — 

Volume  in  Table 

corresponding 

to  reading. 

Volume  of  air  taken     .         .         .  ISO'S         132 '15 

Volume  after  absorption  of  oxygen  1 

by  potassic  hydrate  and   pyro-V         103'5         104*46 
gallic  acid        .         .         .         .J 
132-15 
104-46 
27'69  volumes  of  oxygen  in  132*15  of  air. 

132-15  :  27-69  :  :  100  :  20'953  percentage  of  oxygen  in  air. 

B-ussell  has  also  employed  his  apparatus  for  the  analysis  of 
carbonates  (/.  C.  S.  [N.S.]  vi.  310).  For  this  purpose  he  adapted 
a  graduated  tube,  open  at  both  ends,  to  a  glass  flask  by  means  of 
a  thick  piece  of  caoutchouc  tube.  Into  the  flask  a  weighed 
quantity  of  a  carbonate  was  placed,  together  with  a  vessel 


492 


VOLUMETRIC  ANALYSIS. 


§  98. 


containing  dilute  acid.  The  position  of  the  mercury  in  the 
graduated  tube  was  first  read  off,  after  which  the  flask  was  shaken 
so  as  to  bring  the  acid  and  carbonate  in  contact,  and  the  increase  in 
volume  was  due  to  the  carbonic  anhydride  evolved.  The  results 
thus  obtained  are  extremely  concordant. 

In  eight  experiments  with  sodic  carbonate  the  percentage  of 
carbonic  anhydride  found  varied  from  41*484  to  41*607,  theory 
requiring  41*509. 

Thirteen  experiments  with  calc-spar  gave  from  43*520  to  43*858, 
the  theoretical  percentage  being  44*0 ;  and  in  nine  other  analyses 
from  43*581  to  43*901  were  obtained. 

Two  experiments  were 
made  with  manganic  per- 
oxide, oxalic  acid  and  sul- 
phuric acid,  and  gave  58*156 
and  58*101  per  cent,  of 
carbonic  anhydride. 

Some  determinations  of 
the  purity  of  magnesium 
were  also  performed  by  dis- 
solving the  metal  in  hydro- 
chloric acid  and  measuring 
the  resulting  hydrogen. 
Four  operations  gave  num- 
bers varying  between  8*255 
and  8*282.  The  metal 
should  yield  8*333. 

Russell  has  also  em- 
ployed this  process  for  the 
determination  of  the  com- 
bining proportions  of  nickel 
and  cobalt  (J.  C.  S.  [N.S.] 
vii.  294). 

Regnault  and  Reiset 
described  (Ann.  Cliim.Phys. 
[3]  xxvi.  333)  an  appara- 
tus by  which  absorptions 
could  be  rapidly  conducted 
by  means  of  liquid  reagents 
brought  in  contact  with  the 
gases  in  a  laboratory  tube.  Tig.  85. 

The  measurements  are  made 

in  a  graduated  tube,  which  can  be  placed  in  communication  with 
the  laboratory  tube  by  means  of  fine  capillary  tubes  provided  with 
stop-cocks,  the  lower  end  of  the  measuring  tube  being  connected  by 
an  iron  socket  and  stop-cock  with  another  graduated  tube  in  which 
the  pressure  to  which  the  gas  is  subjected  is  measured.  The 
measuring  and  pressure  tubes  are  surrounded  by  a  cylinder  of  water. 


§    98.  FRANKLAND  AND  WARD'S  APPARATUS.  493 

An  apparatus  similar  in  principle  to  this  has  recently  been 
constructed  by  Franklancl,  and  is  fully  described  in  the  section 
on  Water  Analysis  (§  88,  page  392). 

Frankland  and  Ward  (J.  C.  S.  vi.  197)  made  several 
important  improvements  in  the  apparatus  of  Regnault  and 
Reiset.  They  introduced  a  third  tube  (fig.  85),  closed  at  the  top 
with  a  stopper,  and  which  is  made  to  act  as  a  barometer,  to  indicate 
the  tension  of  the  gas  in  the  measuring  tube,  thus  rendering  the 
operation  entirely  independent  of  variations  of  atmospheric  pressure. 
The  correction  for  aqueous  vapour  is  also  eliminated,  by  introducing 
a  drop  of  water  into  the  barometer  as  well  as  into  the  measuring 
tube,  the  pressures  produced  by  the  aqueous  vapour  in  the  two 
tubes  thus  counterbalancing  one  another,  so  that  the  difference  of 
level  of  the  mercury  gives  at  once  the  tension  of  the  dry  gas.  The 
measuring  tube  is  divided  into  ten  equal  divisions  (which,  for  some 
purposes,  require  to  be  calibrated),  and  in  one  analysis  it  is 
convenient  to  make  all  the  measurements  at  the  same  division,  or 
to  calculate  the  tension  which  would  be  exerted  by  the  gas  if 
measured  at  the  tenth  division.  Frankland  and  Ward  also 
adapted  an  iron  tube  more  than  760  m.m.  long  at  the  bottom  of 
the  apparatus,  which  enables  the  operator  to  expand  the  gas  to  any 
required  extent,  and  thus  diminish  the  violence  of  the  explosions 
which  are  performed  in  the  measuring  tube.  During  the  operation 
a  constant  stream  of  water  is  kept  flowing  through  the  cylinder, 
which  maintains  an  uniform  temperature. 

By  the  use  of  this  form  of  apparatus  the  calculations  of  analyses 
are  much  simplified.  An  example  of  an  analysis  of  atmospheric 
air  will  indicate  the  method  of  using  the  instrument. 


Volume  of   Air  used.     Determined  at  5th  Division  on 
the  Measuring  Tube. 

m.m. 

Observed  height  of  mercury  in  barometer  .     673*0 

Height  of  5th  division        .         .         .         .         .     383'0 

Tension  of  gas         .     290*0 
0-5 


Corrected  tension  of  gas  at  10th  division  145*00 


Volume  after   Admission   of    Hydrogen.      Determined 
at  6th  Division. 

m.m. 

Observed  height  of  mercury  in  barometer  .     772*3 

Height  of  6th  division       .         .      :'..: •"•'••'.         .     304*0 

Tension  of  gas  .     468*3 
0*6 
Corrected  tension  at  10th  division  280*98 


494  VOLUMETRIC  ANALYSIS.  §    98. 

Volume  after  Explosion.     Determined  at  5tli  Division. 


m.m. 


Observed  height  of  mercury  in  barometer  .         .     763 '3 
Height  of  5th  division       .         .         .     '    .         .     383'Q 

Tension  of  gas         .     380-3 
0-5 


Corrected  tension  at  10th  division       .         .         .     190*15 

Tension  of  air  with  hydrogen  .         .         .  2 80 '98 

Tension  of  gas  after  explosion  ....  190*15 

Contraction  on  explosion  .         .         .  90 '83 
of  which  one-third  is  oxygen. 

90'83 

— o —  =  30 "2 7 6  =  volumes  of  oxygen  in  145*0  volumes  of  air 

145*0     :     30-276     :  :     100     :     x 
30-276  x  100     OAQ 
x  — 14.5.0 ~  ~  Percen^aoe  °*  oxygen  m  air. 

If  all  the  measurements  had  been  made  at  the  same  division,  no 
correction  to  the  tenth  division  would  have  been  necessary,  as  the 
numbers  would  have  been  comparable  among  themselves. 

Another  modification  of  Frankland  and  Ward's,  or 
Regnault's  apparatus  has  been  designed  by  McLeod  (J.  C.  S. 
[N.S.]  vii.  313),  in  which  the  original  pressure  tube  of  Kegnault's 
apparatus,  or  the  filling  tube  of  Frankland  and  Ward,  is 
dispensed  with,  the  mercury  being  admitted  to  the  apparatus 
through  the  stop-cocks  at  the  bottom. 

The  measuring  tube  A  (fig.  86)  is  900  m.m.  in  length,  and  about 
20  m.m.  in  internal  diameter.  It  is  marked  with  ten  divisions,  the 
first  at  25  m.m.  from  the  top,  the  second  at  50,  the  third  at  100, 
and  the  remaining  ones  at  intervals  of  100  m.m.  In  the  upper 
part  of  the  tube,  platinum  wires  are  sealed,  and  it  is  terminated  by 
a  capillary  tube  and  fine  glass  stop-cock,  a,  the  capillary  tube  being 
bent  at  right  angles  at  50  m.m.  above  the  junction.  At  the  bottom 
of  the  tube,  a  wide  glass  stop-cock  b  is  sealed,  which  communicates, 
by  means  of  a  caoutchouc  joint  surrounded  with  tape  and  well 
wired  to  the  tubes,  with  a  branch  from  the  barometer  tube  B. 
This  latter  tube  is  5  m.m.  in  width,  and  about  1200  m.m.  long, 
and  is  graduated  in  millimeters  from  bottom  to  top.  At  the  upper 
extremity  a  glass  stop-cock  d  is  joined,  the  lower  end  being  curved 
and  connected  by  caoutchouc  with  a  stop-cock  and  tube  C, 
descending  through  the  table  to  a  distance  of  900  m.m.  below  the 
joint.  It  is  advisable  to  place  washers  of  leather  at  the  end  of  the 
plugs  of  the  stop-cocks  c  and  Z>,  as  the  pressure  of  the  mercury 
which  is  afterwards  to  be  introduced  has  a  tendency  to  force  them 
out ;  if  this  should  happen,  the  washers  prevent  any  great  escape 
of  mercury. 


98.  MC  LEOD'S  APPARATUS.  495 


Fig.  86. 

HUBERT  DYER. 


496  VOLUMETRIC  ANALYSIS.  §    98. 

The  two  tubes  are  firmly  held  by  a  clamp  D,  on  which  rests  a 
wide  cylinder  E,  about  55  m.m.  in  diameter,  surrounding  the  tubes, 
and  adapted  to  them  by  a  water-tight  caoutchouc  cork  F.  The 
cylinder  is  maintained  in  an  upright  position  by  a  support  at  its 
upper  end  G,  sliding  on  the  same  rod  as  the  clamp.  Around  the 
upper  part  of  the  barometer  tube  a  syphon  H  is  fixed  by  means  of 
a  perforated  cork,  through  which  the  stop-cock  d  passes.  A  small 
bulb-tube  e,  containing  some  mercury,  is  also  fitted  in  this  cork,  so 
as  to  allow  of  the  air  being  entirely  removed  from  the  syphon.  The 
syphon  descends  about  100  m.m.  within  the  cylinder,  and  has  a 
branch  at  the  top  communicating  by  caoutchouc  with  a  bent  tube 
contained  in  a  wider  one  J  affixed  to  the  support.  A  constant 
current  of  water  is  supplied  to  the  cylinder  through  a  glass  tube, 
which  passes  to  the  bottom,  and  escapes  through  the  syphon  and 
tubes  to  the  drain. 

To  the  end  of  the  narrow  tube  C  is  fastened  a  long  piece  of 
caoutchouc  tube  K,  covered  with  tape,  by  which  a  communication 
is  established  with  the  mercurial  reservoir  L,  suspended  by  a  cord 
so  that  by  means  of  the  winch  M,  it  may  be  raised  above  the  level 
of  the  top  of  the  barometer  tube.  As  the  mercury  frequently  forces 
its  way  through  the  pores  of  the  caoutchouc  tube,  it  is  advisable 
to  surround  the  lower  part  with  a  piece  of  wide  flexible  tube ;  this 
prevents  the  scattering  of  the  mercury,  which  collects  in  a  tray 
placed  on  the  floor.  Into  the  bottom  of  the  tray  a  screw  must  be 
put,  to  which  the  end  of  the  glass  tube  is  firmly  attached  by  wire. 
The  capillary  stop-cock  a  is  provided  with  a  steel  cap,  by  means  of 
which  it  may  be  adapted  to  a  short  and  wide  laboratory  tube 
capable  of  holding  about  150  c.c.,  and  identical  in  form  with 
the  one  described  in  the  section  on  Water  Analysis  (§  88).  The 
mercurial  trough  for  the  laboratory  tube  is  provided  with  a  stand 
with  rings,  for  the  purpose  of  holding  two  tubes  containing  gases, 
that  may  be  required. 

The  apparatus  is  used  in  the  same  way  as  Frank  land  and 
Ward's,  except  that  the  mercury  is  raised  and  lowered  in  the  tubes 
by  the  movement  in  the  reservoir  L,  instead  of  by  pouring  it  into 
the  centre  supply-tube. 

To  arrange  the  apparatus  for  use,  the  reservoir  L  is  lowered  to  the 
ground,  and  mercury  poured  into  it.  The  laboratory  tube  being 
removed,  the  stop-cocks  are  all  opened,  and  the  reservoir  gradually 
raised.  When  the  tube  A  is  filled,  the  stop-cock  a  is  closed,  and 
the  reservoir  elevated  until  mercury  flows  through  the  stop-cock  d  at 
the  top  of  the  barometer.  It  is  convenient  to  have  the  end  of 
the  tube  above  the  stop-cock  so  bent  that  a  vessel  can  be  placed 
below  to  receive  the  mercury.  This  bend  must,  of  course,  be  so 
short  that,  when  the  plug  of  the  stop-cock  is  removed,  the  syphon 
will  pass  readily  over.  When  the  air  is  expelled  from  the  barometer 
tube,  the  stop-cock  is  closed.  A  few  drops  of  water  must  next  be 
introduced  into  the  barometer :  this  is  accomplished  by  lowering 


§  98.        MC  LEOD'S  GAS  APPARATUS.         497 

the  reservoir  to  a  short  distance  below  the  top  of  the  barometer,  and 
gently  opening  the  stop-cock  d,  while  a  small  pipette,  from  which 
water  is  dropping,  is  held  against  the  orifice,  the  stop-cock  being 
closed  when  a  sufficient  amount  of  water  has  penetrated  into  the 
tube.  In  the  same  manner,  a  small  quantity  of  water  is  passed  into 
the  measuring  tube.  In  order  to  get  rid  of  any  bubbles  of  air  which 
may  still  linger  in  the  tubes,  the  reservoir  is  lowered  to  the  ground 
so  as  to  produce  a  vacuum  in  the  apparatus ;  in  this  manner  the 
interior  surfaces  of  the  tubes  become  moistened.  The  reservoir  is 
now  gently  raised,  thus  refilling  the  tubes  with  mercury.  Great 
care  must  be  taken  that  the  mercury  does  not  rush  suddenly  against 
the  tops  of  the  measuring  and  barometer  tubes,  which  might  cause 
their  destruction.  This  may  be  avoided  by  regulating  the  flow  of 
mercury  by  means  of  the  stop-cock  c,  which  may  be  conveniently 
turned  by  a  long  key  of  wood,  resting  against  the  upper  table  of 
the  sliding  stand  of  the  mercurial  trough.  When  the  reservoir 
has  again  been  elevated  above  the  top  of  the  barometer,  the 
stop-cocks  of  the  measuring  and  barometer  tubes  are  opened,  and 
the  air  and  water  which  have  collected  allowed  to  escape. 

The  heights  of  the  mercurial  columns  in  the  barometer,  corre- 
sponding to  the  different  divisions  of  the  measuring  tube,  have  now 
to  be  determined.  This  is  done  by  running  out  all  the  mercury 
from  the  tubes,  and  slowly  readmitting  it  until  the  meniscus  of  the 
mercury  just  touches  the  lowest  division  in  the  measuring  tube. 
This  may  be  very  conveniently  managed  by  observing  the  division 
through  a  small  telescope  of  short  focus,  and  sufficiently  close  to  the 
apparatus  to  permit  of  the  key  of  the  stop-cock  c  being  turned,  while 
the  eye  is  still  at  the  telescope.  When  a  reading  is  taken,  the 
black  screen  0  behind  the  apparatus  must  be  moved  by  means  of 
the  winch  P,  until  its  lower  edge  is  about  a  millimeter  above  the 
division.  The  telescope  is  now  directed  to  the  barometer  tube,  and 
the  position  of  the  mercury  carefully  noted.  As  the  tubes  only 
contain  aqueous  vapour,  and  are  both  of  the  same  temperature,  the 
columns  in  the  two  tubes  are  those  which  exactly  counterbalance 
one  another,  and  any  difference  of  level  that  may  be  noticed  is  due 
to  capillarity. 

The  same  operation  is  now  repeated  at  each  division  of  the  tube. 
The  measuring  tube  next  requires  calibration,  an  operation  performed 
in  a  manner  perfectly  similar  to  that  described  in  §  88  (page  395), 
namely,  by  filling  the  measuring  tube  with  water,  and  weighing  the 
quantities  contained  between  every  two  divisions.  The  eudiometer 
being  filled  with  water,  and  the  stop-cock  b  closed,  the  reservoir  is 
raised  and  the  mercury  allowed  to  rise  to  the  top  of  the  barometer. 
The  capillary  stop-cock  a  having  been  opened,  the  cock  b  is  gently 
turned,  and  the  water  allowed  to  flow  out  until  the  mercury  reaches 
the  lowest  division  of  the  tube.  A  carefully  weighed  flask  is  now 
supported  just  below  the  steel  cap,  the  stop-cock  b  again  opened, 
until  the  next  division  is  reached,  and  the  quantity  of  water  is 

K   K 


498 


VOLUMETRIC  ANALYSIS. 


§  98. 


weighed,  the  temperature  of  the  water  in  the  wide  cylinder  being 
observed.  The  same  operation  is  repeated  at  each  division,  and  by 
calculation  the  exact  contents  of  the  tube  in  cubic  centimeters  may 
be  found. 

In  this  manner,  a  table,  such  as  the  following,  is  obtained  : — 


Division 
on 

measuring 
tube. 

Height  of  Mercury  in 
Barometer  tube 
corresponding  to 
division. 

Contents. 

Cubic  Centimeters. 

Log. 

1 

756-9 

8-6892 

0-9389814 

2 

706-7 

18-1621 

1-2591664 

3 

606-8 

36-9307 

1-5673880 

4 

506-5 

55-7344 

1-7461232 

5 

406-8 

74-4299 

1-8717477 

6 

306-8 

93-3306 

1-9700244 

7 

206-9 

112-4165 

2-0508303 

8 

107-0 

131-6335 

2-1193666 

9 

7-1 

151-1623 

2-1794435 

When  a  gas  is  to  be  analyzed,  the  laboratory  tube  is  filled  with 
mercury,  either  by  sucking  the  air  out  through  the  capillary 
stop-cock,  while  the  open  end  of  the  tube  stands  in  the  trough,  or 
much  more  conveniently,  by  exhausting  the  air  through  a  piece  of 
flexible  tube  passed  under  the  mercury  to  the  top  of  the  laboratory 
tube,  the  small  quantity  of  air  remaining  in  the  stop-cock  and  at 
the  top  of  the  wide  tube  being  afterwards  very  readily  withdrawn. 
The  face  of  one  of  the  steel  pieces  is  greased  with  a  small  quantity 
of  resin  cerate,  and,  the  measuring  apparatus  being  full  of  mercury, 
the' clamp  is  adjusted. 

Before  the  introduction  of  the  gas,  it  is  advisable  to  ascertain  if 
the  capillary  tubes  are  clear,  as  a  stoppage  may  arise  from  the 
admission  of  a  small  quantity  of  grease  into  one  of  them.  For 
this  purpose  the  globe  L  is  raised  above  the  level  of  the  top  of  the 
measuring  tube,  and  the  capillary  stop-cocks  opened ;  if  a  free 
passage  exists,  the  mercury  will  be  seen  to  flow  through  the  tubes. 
The  stop-cock  of  the  laboratory  tube  is  now  closed.  When  all  is 
properly  arranged,  the  gas  is  transferred  into  the  laboratory  tube, 
and  the  stop-cock  opened,  admitting  a  stream  of  mercury.  The 
cock  c  is  gently  turned,  so  as  just  to  arrest  the  flow  of  mercury 
through  the  apparatus,  and  the  reservoir  lowered  to  about  the  level 
of  the  table,  which  is  usually  sufficient.  By  carefully  opening  the 
cock  c,  the  gas  is  drawn  over  into  the  measuring  tube,  and  when 
the  mercury  has  reached  a  point  in  the  capillary  tube  of  the 
laboratory  tube,  about  midway  between  the  bend  and  the  stop-cock, 
the  latter  is  quickly  closed.  It  is  necessary  that  this  stop-cock 
should  be  very  perfect.  This  is  attained  by  grinding  the  plug  into 


§  98.        MC  LEOD'S  GAS  APPARATUS.         499 

the  socket  with  fine  levigated  rouge  and  solution  of  sodic  or  potassic 
hydrate.  By  this  means  the  plug  and  socket  may  be  polished  so 
that  a  very  small  quantity  of  resin  cerate  and  a  drop  of  oil  renders 
it  perfectly  gas-tight.  In  grinding,  care  must  be  taken  that  the 
operation  is  not  carried  011  too  long,  otherwise  the  hole  in  the  plug 
may  not  coincide  with  the  tubes.  If  this  stop-cock  is  in  sufficiently 
good  order,  it  is  unnecessary  to  close  the  stop-cock  a  during  an  analysis. 

The  mercury  is  allowed  to  flow  out  of  the  apparatus  until  its 
surface  is  a  short  distance  below  the  division  at  which  the  measure- 
ments are  to  be  made.  The  selection  of  the  division  depends  on 
the  quantity  of  gas  and  the  kind  of  experiment  to  be  performed 
with  it.  A  saving  of  calculation  is  effected  if  all  the  measurements 
in  one  analysis  are  carried  on  at  the  same  division.  When  the 
mercury  has  descended  below  the  division,  the  cock  c  is  closed,  the 
reservoir  raised,  and  the  black  screen  moved  until  its  lower  edge  is 
about  a  millimeter  above  the  division,  and  the  telescope  placed  so 
that  the  image  of  the  division  coincides  with  the  cross- wires  in  the 
eye-piece.  The  stop-cock  c  is  now  gently  opened  until  the  meniscus 
just  touches  the  division ;  the  cock  is  closed  and  the  height  of  the 
mercury  in  the  barometer  is  measured  by  means  of  the  telescope. 
The  difference  between  the  reading  of  the  barometer,  and  the 
number  in  the  table  corresponding  to  the  division  at  which  the 
measurement  is  taken,  gives  in  millimeters  the  tension  of  the  gas. 
The  volume  of  the  gas  is  found  in  the  same  table,  and  with  the 
temperature,  which  is  read  off  at  the  same  time  as  the  pressure,  all 
the  data  required  for  the  calculation  of  the  volume  of  the  gas  at 
0°  and  760  m.m.  are  obtained.  No  correction  is  required  for 
tension  of  aqueous  vapour ;  the  measuring  tube  and  barometer  tube 
being  both  moist,  the  tensions  in  the  tubes  are  counterbalanced. 
Absorptions  are  performed  with  liquid  reagents  by  introducing  a  few 
drops  of  the  liquid  into  the  laboratory  tube,  transferring  the  gas 
into  it,  and  allowing  the  mercury  to  drop  slowly  through  the  gas  for 
about  five  minutes.  The  gas  is  then  passed  over  into  the  measuring 
tube,  and  the  difference  of  tension  observed  corresponds  to  the 
amount  of  gas  absorbed.  It  is  scarcely  necessary  to  add,  that  the 
greatest  care  must  be  taken  to  prevent  any  trace  of  the  reagent 
passing  the  stop-cock.  If  such  an  accident  should  occur,  the 
measuring  tube  must  be  washed  out  several  times  with  distilled 
water  at  the  conclusion  of  the  analysis.  If  the  reagent  is  a  solution 
of  potassic  hydrate  it  may  be  got  rid  of  by  introducing  into  the  tube 
some  distilled  water,  to  which  a  drop  of  sulphuric  acid  has  been 
added.  If  this  liquid  is  found  to  be  acid  on  removing  it  from  the 
tube,  it  may  be  presumed  that  all  the  alkali  has  been  neutralized. 

When  explosions  are  to  be  performed  in  the  apparatus,  the 
gas  is  first  measured  and  then  returned  to  the  laboratory  tube. 
A  quantity  of  oxygen  or  hydrogen,  as  the  case  may  be,  which  is 
judged  to  be  the  proper  volume,  is  transferred  into  the  laboratory 
tube,  and  some  mercury  is  allowed  to  stream  through  the  gases  so 

K  K  2 


500  VOLUMETEIC  ANALYSIS.  §    98. 

as  to  mix  them  thoroughly.  The  mixture  is  next  passed  into  the 
eudiometer  and  measured.  If  a  sufficient  quantity  of  the  second 
gas  has  not  been  added,  more  can  readily  be  introduced.  After 
the  measurement,  it  may  be  advisable  to  expand  the  mixture,  in 
order  to  diminish  the  force  of  the  explosion.  This  is  done  by 
allowing  mercury  to  flow  out  from  the  tube  into  the  reservoir. 
"When  the  proper  amount  of  expansion  has  been  reached,  the 
stop-cocks  a  and  b  are  closed.  To  enable  the  electric  spark  to  pass 
between  the  wires,  it  is  necessary  to  lower  the  level  of  the  water  in 
the  cylinder.  For  this  purpose,  the  bent  glass  tube  at  the  extremity 
of  the  syphon  is  made  to  slide  easily  through  the  cork  which  closes 
the  top  of  the  wide  tube  J.  By  depressing  the  bent  tube,  the 
water  flows  out  more  rapidly  than  before,  and  the  level  consequently 
falls.  "When  the  surface  is  below  the  eudiometer  wires,  a  spark 
from  an  induction-coil  is  passed,  exploding  the  gas.  The  syphon 
tube  is  immediately  raised,  and,  when  the  water  in  the  cylinder  has 
reached  its  original  level,  the  gas  is  cool  enough  for  measurement. 
900  c.c.  of  mercury  are  amply  sufficient  for  the  whole  apparatus ; 
and  as  there  is  no  cement  used  to  fasten  the  wide  tubes  into  iron 
sockets,  a  great  difficulty  in  the  original  apparatus  is  avoided. 

The  following  details  of  an  analysis,  in  which  absorptions  only 
were  performed,  will  show  the  method  employed.  The  gas  was 
a  mixture  of  nitrogen,  oxygen,  and  carbonic  anhydride,  and  the 
measurements  were  all  made  at  division  No.  1  on  the  eudiometer, 
which  has  been  found  to  contain  8*6892  c.c. 

Original   Gas. 

m.in. 

Temperature  of  water  in  cylinder,  15 '4°. 

Height  of  mercury  in  barometer  tube          ....  980*5 

„         „              corresponding  to  Division  No.  1  (see 
Table) 756*9 

Pressure  of  the  gas 223 -6 

After  absorption  of  the  carbonic  anhydride  by  solution 
of  potassic  hydrate — 

Height  of  mercury  in  barometer  tube          .         .         .         .  941 '7 
„         ,,  corresponding  to  Division  No.  1          .  756 '9 

Pressure  of  the  gas  after  removal  of  carbonic  anhydride       .  184*8 

Pressure  of  original  gas      .         .         .         .<        .         .         .223*6 
„  gas  after  removal  of  carbonic  anhydride     .         .   184*8 

Tension  of  carbonic  anhydride   .         ;.         .          .         .          .38*8 

After  absorption  of  the  oxygen  by  potassic  pyrogallate — 
Height  of  mercury  in  barometer  tube          .  -      .         .         .   885*4 
„         „  corresponding  to  Division  No.  1         .  756*9 

Pressure  of  nitrogen.         .         .         .         .;        .        »         .   128*5 


§  93- 


CALCULATIONS. 


501 


Pressure  of  oxygen  and  nitrogen 
„  nitrogen . 


.     ,•   .         .         .  184-8 
,     %  .         .         .         .   128-5 

„  oxygen   .         .         .         ...         .         .     56*3 

These  measurements,  therefore,  give  us  the  following  numbers  :  — 

tn.m. 

Pressure  of  nitrogen  .         .         .         .         .         .         .128*5 

oxygen    .  ....         .         .         .         .         .-,    56'3 

,,  carbonic  anhydride  .         .         .;        .         .  3  8  '8 

„  original  gas      .         .         .         .         ...         .  223  -6 

If  the  percentage  composition  of  the  gas  is  required,  it  is  readily 
obtained  by  a  simple  proportion,  the  temperature  having  remained 
constant  during  the  experiment  :  — 

111.111.  711.  1U.  m.Hl, 

223-6  :  128-5  :  :  100  :  57  "469  per  cent.  N" 
223-6  :  56-3  :  :  100  :  25'179  per  cent.  0 
223-6  :  38-8  :  :  100  :  17'352  per  cent.  CO2 

100-000 

If,  however,  it  is  necessary  to  calculate  the  number  of  cubic 
centimeters  of  the  gases  at  0°  and  760  m.m.,  it  is  done  by  the 
following  formulae  :  — 

8-6892x128-5 


760  x[l  +(0-003665  xl5-4) 

8-6892  x  56-3 
760  x[l+  (0-003665  xl5-4) 

8-6892  x  38-8 
760  x[l+  (0-003665x15-4)] 

8-6892  x  223-6 
760  x[l+  (0-003665x15-4)] 


°'6093 


of 


of 


of  carbonic  anhydride- 


=          8  c'c"  of  the 


If  many  of  the  calculations  are  to  be  done,  they  may  be  very 
much  simplified  by  constructing  a  table  containing  the  logarithms 
of  the  quotients  obtained  by  dividing  the  contents  of  each  division 
of  the  tube  by  760  x  (1  +  0-003665*).  The  following  is  a  very 
short  extract  from  such  a  table  :  — 


T°. 

Division  No.  1. 
8-6892 

Division  No.  2. 
18-1621 

-^760  x  (1  +  5*). 

Log'760  x  (1  +  §t). 

15-0 

2-03492 

2-35511 

•1 

2-03477 

2-35496 

•2 

2-03462 

2-35481 

•3 

2-03447 

2-35466 

•4 

2-03432 

2-34451 

502 


VOLUMETEIC   ANALYSIS. 


§  98. 


By  adding  the  logarithms  of  the  tensions  of  the  gases  to  those 
in  the  above  table,  the  logarithms  of  the  quantities  of  gases  are 
obtained ;  thus  : — 

Log.  corresponding  to  Division  ~No.  1, 

and  15-4°  •  2-03432 


Log.  128 '5  =  pressure  of  nitrogen 

Log.  of  quantity  of  nitrogen 
Volume    of    nitrogen    at    0° 
760  m.m. 


and 


2-10890 

0-14322 -log.  1-3906 

1-3906  c.c. 

2-03432 

1-75051 

1-78483  =  log.  0-6093 

0-6093  c.c. 
2-03432 

1-58883 

1-62315  =log.  0-4199 

0-4199  c.c. 

2-03432 
Log.  223 '6  =  pressure  of  original  gas     2*34947 

Log.  of  quantity  of  original  gas          .     0-38379  =  log.  2*4198 
Volume'  of  original  gas  at  0°  and 
760  m.m. 


Log.  56 -3  =  pressure  of  oxygen 

Log.  of  quantity  of  oxygen 

Volume  of  oxygen  at  0°  and 
760  m.m.  . 

Log.  38'8  =  pressure  of  carbonic  anhy- 
dride ...... 

Log.  of   quantity  of   carbonic  anhy- 
dride  ...... 

Volume  of  carbonic  anhydride  at 
0°  and  760  m.m. 


2-4198  c.c. 


Nitrogen 

Oxygen 

Carbonic  anhydride 

Total 


1-3906 
0-6093 
0-4199 


or 
or 
or 


1-391  c.c. 
0-609  c.c. 
0-420  c.c. 


2-4198     or     2-420  c.c. 


The  following  example  of  an  analysis  of  coal  gas  will  show  the 
mode  of  working  with  this  apparatus,  and  the  various  operations  to 
be  performed  in  order  to  determine  the  carbonic  anhydride,  oxygen, 
hydrocarbons  absorbed  by  Nordhausen  sulphuric  acid,  hydrogen, 
marsh  gas,  carbonic  oxide,  and  nitrogen. 

The  measuring  tube  and  laboratory  tube  were  first  filled  with 
mercury,  some  of  the  gas  introduced  into  the  laboratory  tube,  and 
passed  into  the  apparatus. 

The  gas  was  measured  at  the  second  division. 

Height  of  mercury  in  the  barometer  tube  .     989 -0 

„  „  ,,       measuring  tube  .     706  -8 

Pressure  of  the  gas  at  16-6°     282'2 


§    98.  MEASUREMENT   OF   GASES.  503 

Two  or  three  drops  of  a  solution  of  potassic  hydrate  were 
now  placed  in  the  laboratory  tube,  and  the  gas  passed  from  the 
measuring  tube,  the  mercury  being  allowed  to  drop  through  the 
gas  for  ten  minutes.  On  measuring  again — 

Height  of  mercury  in  barometer  .         .         .     984*0 

Some  saturated  solution  of  pyrogallic  acid  was  introduced  into 
the  laboratory  tube,  and  the  gas  left  in  contact  with  the  liquid  for 
ten  minutes.  On  measuring — 

Height  of  mercury  in  barometer          .         .         .     983 '6 

Height  of  mercury  when  measuring  original  gas       989'0 
„  „         after  absorption  of  CO2          .     984*0 

Pressure  of  CO2         5*0 

after  absorption  of  CO2          .     984*0 
after  absorption  of  0    .         .     983*6 

Pressure  of  0         0*4 

The  volumes  of  the  gases  being  proportional  to  their  pressures,  it 
is  simple  to  obtain  the  percentages  of  carbonic  anhydride  and 
oxygen  in  the  original  gas. 

Original  gas.  CQ2 

282*2       :       5*0       ::       100       :       1*772  per  cent.  CO2 

Original  gas.  O 

282*2       :       0*4       :  :       100       :      0*142  per  cent.  0 

1*914 

By  subtracting  1*914  from  100,  we  obtain  the  remainder, 
98*086,  consisting  of  the  hydrocarbons  absorbed  by  Nordhausen 
sulphuric  acid,  hydrogen,  carbonic  oxide,  marsh  gas,  and  nitrogen ; 
thus : — 

Original  gas  .         . 100*000 

0  and  CO2 1*914 

CnH2n.  H.  CO.  CH4.  N  98*086 

"While  the  gas  remains  in  the  measuring  tube,  the  laboratory  tube 
is  removed,  washed,  dried,  filled  with  mercury,  and  again  attached 
to  the  apparatus.  Much  time  is  saved  by  replacing  the  laboratory 
tube  by  a  second,  which  was  previously  ready.  As  a  minute 
quantity  of  gas  is  lost  in  this  operation,  in  consequence  of  the 
amount  between  the  stop-cocks  being  replaced  by  mercury,  it  is 
advisable  to  pass  the  gas  into  the  laboratory  tube,  then  transfer  it 
to  the  eudiometer,  and  measure  again. 

On  remeasuring,  the  mercury  in  the  barometer 

stood  at         .         .         ....         .     983*3 

The  mercury  in  the  measuring  tube    .         .         .     706*8 

Pressure  of  CnH2n.  H.  CO.  CH4.  IsT     276*5 


504  VOLUMETRIC   ANALYSIS.  §    98. 

The  gas  is  again  passed  into  the  laboratory  tube,  and  a  coke  ball, 
soaked  in  fuming  sulphuric  acid,  left  in  contact  with  the  gas  for 
an  hour ;  the  bullet  is  then  withdrawn,  and  some  potassic  hydrate 
introduced  and  left  in  the  tube  for  ten  minutes,  in  order  to  remove 
the  vapours  of  sulphuric  anhydride,  and  the  sulphurous  and 
carbonic  anhydrides  formed  during  the  action  of  the  Nordhausen 
acid  on  the  gas.  The  gas  is  now  measured  again. 

Height  of  mercury  in  barometer  tube          .         .  969*3 
„                 „                 „            before  absorbing 

CnH2ii 983-3 

after  .  969'3 

Pressure  of  CnH2n       14-0 

The  percentage  of  these  hydrocarbons  is  thus  found  : — 
Gas  containing  CnH2n.  H.  CO.  CH4.  X. 

CnH2n. 

276-5     :     14-0     ::     98*086     :     £966  per  cent.  CnH2n 

It  now  remains  to  determine  the  hydrogen,  carbonic  oxide,  marsh 
gas,  and  nitrogen  in  a  portion  of  the  residual  gas.  The  laboratory 
tube  is  therefore  removed,  some  of  the  gas  allowed  to  escape,  and 
another  laboratory  tube  adapted  to  the  apparatus.  The  portion  of 
gas  remaining  is  expanded  to  a  lower  ring  (in  this  special  case  to 
the  third  division),  and  the  tension  measured : — 

Height  of  mercury  in  the  barometer  tube   .         .     642 -2 
„  ,,          measuring  tube  .         .     606'7 

Pressure  of  residue       35 '5 

An  excess  of  oxygen  has  now  to  be  added.  For  this  purpose 
the  gas  is  passed  into  the  laboratory  tube,  and  about  five  times  its 
volume  of  oxygen  introduced  from  a  test  tube  or  gas  pipette.  The 
necessary  quantity  of  oxygen  is  conveniently  estimated  by  the  aid 
of  rough  graduations  on  the  laboratory  tube,  which  are  made  by 
introducing  successive  quantities  of  air  from  a  small  tube  in  the 
manner  previously  described  for  the  calibration  of  the  eudiometers. 

After  the  introduction  of  the  oxygen,  the  mixed  gases  are  passed 
into  the  eudiometer  and  measured. 

Height    of    mercury   in    the    eudiometer    after 

addition  of  0         .         .....         .     789'5 

The  mixture  has  now  to  be  exploded,  and  when  the  pressure  is 
considerable,  it  is  advisable  to  expand  the  gas  so  as  to  moderate  the 
violence  of  the  explosion.  When  sufficiently  dilated,  the  stop-cock 
at  the  bottom  of  the  eudiometer  is  closed,  the  level  of  the  water 
lowered  beneath  the  platinum  wires  by  depressing  the  syphon,  and 
the  spark  passed.  The  explosion  should  be  so  powerful  that  it 
should  be  audible,  and  the  flash  visible  in  not  too  bright  daylight. 


§    98.  MEASUREMENT   OF   GASES.  505 

The  stop-cock  at  the  bottom  of  the  eudiometer  is  now  opened, 
and  the  gas  measured. 

Height  of  mercury  in  barometer  after  explosion  .     732*5 

The  difference  between  this  reading  and  the  previous  one  gives 
the  contraction  produced  by  the  explosion  : — 

Height  of  mercury  in  barometer  before  explosion     789*5 

after          „  732*5 

Contraction  =  C       57*0 

It  is  now  necessary  to  estimate  the  amount  of  carbonic  anhydride 
formed.  This  is  done  by  absorbing  with  potassic  hydrate  as  before 
described. 

Height    of    mercury   in    barometer    tube    after 

absorbing  CO2        .         .         .         ..       , .         .     715*8 

This  number  deducted  from  the  last  reading  gives  the  carbonic 
anhydride. 

Height  of  mercury  in  barometer  after  exploding       732 '5 
„      after  absorbing  CO2     715*8 

Carbonic  anhydride  =  D       16*7 

It  now  remains  to  determine  the  quantity  of  oxygen  which  was 
not  consumed  in  the  explosion,  and  which  excess  now  exists  mingled 
with  the  nitrogen.  For  this  purpose,  a  volume  of  hydrogen  about 
three  times  as  great  as  that  of  the  residual  gas  is  added,  in  the  same 
way  as  the  oxygen  was  previously  introduced,  and  the  pressure  of 
the  mixture  determined. 

Height  of  mercury  in  barometer  after  adding  H     1031*3 
This  mixture  is  exploded  and  another  reading  taken. 

Height  of  mercury  in  barometer  after  exploding 

withH  .         ;  .         .         .     706*7 

This  number  subtracted  from  the  former,  and  the  difference 
divided  by  3,  gives  the  excess  of  oxygen. 

Height  of  mercury  in  barometer  before  exploding 

with  H  .  ...  .  .  .  1031*3 

Height  of  mercury  in  barometer  after  exploding 

withH  .  *  .  .  .  .  .  .  706*7 

3)  324*6 

Excess  of  oxygen     108*2 

In  order  to  obtain  the  quantity  of  nitrogen  in  the  gas  analyzed, 
this  number  has  to  be  deducted  from  the  volume  of  gas  remaining 
after  the  explosion  with  oxygen  and  the  removal  of  the  carbonic 
anhydride. 


506  VOLUMETRIC  ANALYSIS.  §    98. 

Height  of  mercury  in  barometer  after  absorbing 

CO2 715-8 

„  „         in  eudiometer  at  division  No.  3     606*7 

Nitrogen  and  excess  of  oxygen  .         .         .  109'1 

Excess  of  oxygen       .         .         .         .         .  108 -2 

Nitrogen         0*9 

"We  have  now  all  the  data  necessary  for  the  calculation  of  the 
composition  of  the  coal  gas.  It  is  first  requisite  to  calculate  the 
proportion  of  the  combustible  gas  present  in  the  coal  gas,  which  is 
done  by  deducting  the  sum  of  the  percentages  of  gas  determined 
by  absorption  from  100. 

Percentage  of  carbonic  anhydride      .         .         .       1*772 

„  oxygen 0*142 

CnH2n 4-966 

CO2.  0.  CnH2n       6-880 

Original  gas 100 -000 

CO2.  0.  CnH% 6-880 

H.  CO.  CH4.  N     93-120 

The  formulae  for  the  calculation  of  the  analysis  of  a  mixture  of 
hydrogen,  carbonic  oxide,  and  marsh  gas,  are  (see  page  486) — 
Hydrogen          =  x  —  A  -  D 

3A-2C  +  D 

Carbonic  oxide  =  y  = ~ — 

2C-3A  +  2D 
Marsh  gas          =  z  —  —    — « — 

A  =  35-5 -0-9  =  34-6 

C  =  57-0 

D  =  16-7 
A-      34-6 
D=      16-7 

17 -9  =  ^  =  Hydrogen  in  35 -5  of  the  gas  exploded 

with  oxygen. 

A=     34-6  C=     57-0 
3  2 

3A=    103-8                   2C=    114-0 
D=     16-7  


3A  +  D-2C 


2C=   114-0 
3)       6T5 


2*167  =  y  =  Carbonic  oxide  in  35*5  of  the  gas. 


§    98.  ESTIMATION   OF  HYDROCAKBONS.  507 

D=     16-7 

2 

2D  =     33-4 
2C  =    114-0 

21)  +  2C  =    147-4 
3A  =    103-8 

3)  43-6  =  2D  +  2C-3A 
2D  +  2C-3A=      14.533  =  g5S  Marsh. gas  in  35-5  of  the  gas. 

These  numbers  are  readily  transformed  into  percentages,  thus  : — 

35-5  :  17-9       :  :  93'12  :  46*952  per  cent,  of  Hydrogen. 
35-5  :    2-167  :  :  93'12  :    5'684  per  cent,  of  Carbonic  oxide. 
35-5  :  14-533  :  :  93-12  :  38*122  per  cent,  of  Marsh  gas. 
35-5  :    0-9       :  :  93*12  :    2-361  per  cent,  of  Mtrogen. 

This  completes  the  calculations,  the   results  of    which  are  as 
follows : — 

Hydrogen    .         .         .  .  46'952 

Marsh  gas  .         .         .  .  38-122 

CnH2n        ....  4-966 

Carbonic  oxide    .         .  .  5*684 

Carbonic  anhydride      .  .  1*772 

Oxygen       .         .         .  .  0-142 

Mtrogen     ...  .  2*361 

99*999 


It  is  obvious  that  this  analysis  is  not  quite  complete,  since  it 
does  not  give  any  notion  of  the  composition  of  the  hydrocarbons 
absorbed  by  the  Nordhausen  acid,  To  determine  this,  some  of 
the  original  gas,  after  the  removal  of  carbonic  anhydride  and  oxygen, 
is  exploded  with  oxygen,  and  the  contraction  and  carbonic  anhy- 
dride produced  are  measured.  The  foregoing  experiments  have 
shown  the  effect  due  to  the  hydrogen,  carbonic  oxide,  and  marsh 
gas,  the  excess  obtained  in  the  last  explosion  being  obviously  caused 
by  the  hydrocarbons  dissolved  by  the  sulphuric  acid,  and  from 
these  data  the  composition  of  the  gas  may  be  calculated. 

It  may  be  remarked  that  analyses  of  this  kind  were  performed 
with  the  apparatus  at  the  rate  of  two  a  day  when  working  for 
seven  hours. 

It  may  be  useful  to  show  how  this  analysis  appears  in  the 
laboratory  note  book  : — 


508 


VOLUMETRIC  ANALYSIS. 


§    98. 


Analysis  of  Coal  Gas. 


989-0^ 
706-8  1 

^original 

1      gas 

989-0               984-0 
984-0               983-6 

282  -2  J 

5-0  =  CO2       0-4 

984-0 

Aft.  absorb.  CO2 

282-2  :  5-0  :  :  ] 
282-2  :  0-4  :  :  1 

983-6 
983-3 

Aft.  absorb.  0 
Eemeasured 

100-000 
1-914  CO2.  0 

969-3    Aft.  absorb.  CnH2n 


642-2 
606-7 


732-5 

715-8 

1031-3 
706-7 


Portion  of 
Residue 


with  0 


Aft.  expl. 

Aft.  absorb.  CO2 

withH 
Aft.  expl. 


H  =  x  =  A-D 


1-914 


98-086  CnH2n.  H.  CO.  CH*.  N 

983*3          983-3 
706-8          969-3 

276-5  14-0  CnH2n 

276-5  : 14-0  :  :  98'086  :  4'966  CnH2n 


35-5  =  H.  CO. 

0-9  =  N 


4.  N 


CO2  =  1-772 

0  =  0-142 

CnH2n  =  4-966 


34-6  =  H.  CO.  CH*  =  A 

789-5 
732-5 


6-880 


732-5 
715-8 


57-0  =  contraction  =  C      167  =  CO2  =  D 


1031-3 
706-7 

3)  324-6 
108-2  =  0 


3A  -  2C  +  D 


=  17-9 
=    2-167 


715-8 
606-7 

109-1  =  N  +  0 
108-2  =  0 


0-9  =  N 


34-600 


34-6  =  A 
16-7  =  D 

17-9  =  x  =r  H 


57-0  =  C 
2 

114-0  =  2C 


34-6 
3 


103-8    =  3A 
167    =D 

120-5    =  3  A  +  D 
114-0    =  2C 

3)     6-5    =  3A  +  D  -  2C 
2-167-  y  —  CO 


100-000 
6-880  CO.  0.  CnH2n 

93-120  H.  CO.  CH*.  N 


167    =  D 
2 


33-4    =  2D 
114-0    =  2C 


147-4    =  2C  +  2D 
103-8    =  3A 

3)   43-6    =  2D  +  2C  -  3A 


14-533=  z  = 


35-5  : 17-9      :  :  93-12  :  46'952  H 
35-5  :   2-167  :  :  93-12  :   5-684  CO 
35-5  : 14-533  :  :  93-12  ;  38-122  CH 
35-5  :    0-9      :  :  93-12  :   2-361  N 


§  98.  THOMAS'S  GAS  APPAKATUS.  509 


H  =  46-952 

CH*  '  =  38-122 

CnH2n  =  4-966 

CO  =  5-684 

CO2  =  1772 

O  =  0-142 

N  =  2-361 


99-999 

It  is  assumed  in  the  above  example,  that  the  temperature  of  the 
water  in  the  cylinder  remained  constant  throughout  the  period 
occupied  in  performing  the  analysis.  As  this  very  rarely  happens, 
the  temperature  should  be  carefully  read  off  after  every  measure- 
ment of  the  gas  and  noted,  in  order  that  due  correction  be  made  for 
any  increase  or  decrease  of  volume  which  may  result  in  consequence. 


THOMAS'S    IMPROVED    GAS    APPARATUS. 

In  the  Chemical  Society's  Journal  for  May,  1879,  Thomas 
described  an  apparatus  for  gas  analysis  which  has  the  closed 
pressure  tube  of  Frank  land  and  Ward,  and  is  supplied  with 
mercury  by  means  of  the  flexible  caoutchouc  tube  arrangement  of 
Me  Leod.  The  manner  in  which  this  apparatus  is  filled  with 
mercury  and  got  into  order  for  working  is  so  similar  to  that  already 
described,  that  no  further  reference  need  be  made  thereto. 

The  eudiometer  is  only  450  m.m.  long  from  shoulder  to  shoulder, 
and  the  laboratory  tube  and  mercury  trough  are  under  the  command 
of  the  operator  from  the  floor  level.  The  eudiometer  has  divisions 
20  m.m.  apart,  excepting  the  uppermost,  which  is  placed  as  close 
beneath  the  platinum  wires  as  is  convenient  to  obtain  a  reading. 
The  method  explained  in  sequel  of  exploding  combustible  gases 
under  reduced  pressure,  without  adding  excess  of  gas  to  modify  the 
force  of  the  explosion,  permits  the  shortening  of  the  eudiometer  as 
above,  and  enables  the  apparatus  to  be  so  erected,  that  a  long 
column  of  the  barometer  tube  shall  stand  above  the  summit  of  the 
eudiometer.  By  means  of  such  an  arrangement  a  volume  of  gas 
may  be  measured  under  nearly  atmospheric  pressure,  and  as  this 
pressure  is  equal  to  more  than  700  m.m.,  plus  aqueous  tension,  the 
sensitiveness  of  the  apparatus  is  considerably  augmented.  The 
barometer  tube  is  1000  m.m.  in  length,  having  about  700  m.m. 
lines  above  Division  2  on  the  eudiometer.  The  steel  clamp  and 
facets  forming  the  connections  between  the  eudiometer  and  detach- 
able laboratory  tube  of  the  apparatus  previously  described  are 
dispensed  with,  as  in  this  form  the  eudiometer  and  laboratory 
vessels  are  united  by  a  continuous  capillary  tube,  12  m.m.  (outside) 
diameter,  and  one  three-way  glass  tap  is  employed  in  lieu  of  the 
two  stop-cocks.  The  arrangement  is  simple.  The  glass  tap  is 
hollow  in  the  centre,  and  through  this  hollow  a  communication  is 
made  with  the  capillary,  by  means  of  which  either  the  laboratory 


510  VOLUMETRIC  ANALYSIS.  §    98. 

tube  or  the  eudiometer  can  be  washed  out.  As  the  laboratory 
vessel  is  not  disconnected  for  the  removal  of  the  reagent  used  in 
an  absorption,  it  is  supported  by  a  clamp,  as  shown  in  the  drawing ; 
and  when  it  requires  washing  out  the  mercury  trough  is  turned 
aside,  in  order  that  an  enema  syringe  may  be  used  for  injecting  a 
stream  of  water.  A  few  drops  of  water  are  let  fall  into  the  hollow 
of  the  tap,  and  blown  through  the  capillary  tube  three  times  in 
succession,  so  as  to  get  rid  of  the  absorbent  remaining  in  the 
capillary,  then  the  syringe  is  brought  into  play  once  more,  the 
excess  of  water  removed  by  wiping,  and  the  trough  turned  back 
into  position.  The  laboratory  tube  may  be  refilled  with  mercury 
as  described  on  page  498;  but  it  will  be  found  much  more  serviceable 
if  a  double-acting  syringe,  connected  to  a  bulb  apparatus  (to  catch 
any  mercury  that  may  come  over),  and  then  to  the  orifice  of  the 
hollow  in  the  tap  by  a  ground  perforated  stopper,  be  used,  as  this 
will  obviate  the  destructive  effect  of  heavy  suction  upon  the  gums 
and  teeth.  The  mercury  trough  is  supported  upon  a  guide  which 
travels  over  the  upright  U,  and  is  turned  aside  for  the  purpose  of 
washing  out  the  laboratory  vessel  in  the  following  manner : — The 
spiral  spring  is  depressed  by  means  of  the  tension  rods  until  the 
slot  is  brought  below  the  stud  fixed  in  the  upright  U ;  and  the  top 
ferrule  holding  the  guide  rods  being  movable,  the  trough  can  be 
turned  round  out  of  the  way,  but  is  prevented  from  coming  in 
contact  with  the  glass  water-cylinder  by  an  arrangement  in  the  top 
of  the  guide,  which  comes  against  the  stud  in  the  upright.  The 
height  of  the  trough  can  be  accurately  adjusted  by  the  screw  in  the 
top  of  the  lever  guide.  When  the  trough  is  in  position,  the  clamp 
holding  the  laboratory  vessel  may  be  loosed  when  necessary. 

The  eudiometer  and  barometer  tubes  pass  through  an  india- 
rubber  cork,  asinMcLeod's  apparatus,  but  are  not  supported  by 
the  clamp  C,  which  here  simply  bears  the  water-cylinder.  No 
glass  stop-cocks  are  used,  or  glass-work  of  any  kind  employed  in 
the  construction  of  the  lower  portion  of  the  apparatus.  The  lower 
end  of  the  eudiometer  has  a  neck  of  the  same  outside  diameter  as 
the  barometer  tube  (9 '5  m.m.),  and  both  tubes  are  fixed  into  the 
steel  block  X,  without  rigidity,  by  the  usual  steam  cylinder-gland 
arrangement,  small  india-rubber  rings  being  used  to  form  the 
packing.  The  steel  block  is  fixed  to  the  table  by  a  nut  screwed 
upon  the  f -inch  hydraulic  iron  tube,  which  runs  to  the  bottom  of 
the  table.  The  tap  in  the  steel  block  is  so  devised  that  it  first  cuts 
off  connection  with  the  barometer  tube,  in  order  that  the  gas  may 
be  drawn  over  from  the  laboratory  vessel  into  the  eudiometer  with- 
out risking  the  fracture  of  the  upper  end  of  the  barometer  tube  by 
any  sudden  action  of  the  mercury.  This  precaution  is  necessary,  as 
during  the  transferring  of  the  gas  the  mercury  in  the  barometer 
tube  is  on  the  point  of  lowering,  to  leave  a  vacuous  space  in  the 
summit  of  the  tube.  By  moving  the  handle  a  little  further  on 
the  quadrant  a  communication  is  made  with  both  tubes  and  the 


§  98. 


THOMAS'S  GAS  APPARATUS. 


511 


reservoir  for  the  purpose  of  bringing  the  gas  into  position,  so  as  to 
take  a  reading ;  then  the  handle  is  drawn  a  little  further  to  cut  off 


Fig.  87. 

the  reservoir  supply,  whilst  there  tis  a  way  still  left  between  the 
eudiometer  and   barometer   tubes,  and   if  the   handle   be  drawn. 


512  VOLUMETRIC  ANALYSIS.  §    98. 

forward  a  little  more,  all  communication  is  cut  off  for  the  purpose 
of  exploding. 

The  windlass  P,  for  raising  and  lowering  the  mercury  reservoir  L, 
is  placed  beneath  the  table,  in  order  that  it  may  be  under  command 
from  a  position  opposite  the  laboratory  vessel,  and  it  is  furnished 
with  a  spring  ratchet  motion,  so  as  to  be  worked  by  one  hand.  The 
water-cylinder  should  be  four  inches  in  diameter,  and  the  casing  tube 
of  the  barometer  as  wide  as  practicable,  so  that  the  temperature  of 
the  apparatus  may  be  maintained  as  constant  as  possible.  To  attain 
an  accurate  result  it  is  as  essential  to  keep  the  barometer  tube 
of  uniform  temperature  as  the  eudiometer,  since  the  tension  of 
aqueous  vapour  varies  proportionally.  The  stream  of  water  from 
the  service  main  is  run  into  the  casing  tube  at  the  upper  end  of 
the  barometer,  and,  whilst  the  water-cylinder  is  filling,  the  tap  at 
the  bottom  is  opened  slightly,  so  that  water  may  run  out  very 
slowly.  When  the  water-cylinder  is  full,  the  upright  tube  G  acts 
as  a  syphon,  and  sucks  out  the  excess  of  water  from  the  top  of  the 
cylinder,  thus  keeping  up  the  circulation  at  the  point  where  it  is 
most  required.  For  a  further  detailed  description  of  the  apparatus 
see  /.  C.  £.,  May,  1879. 

There  are  only  two  working  taps  upon  this  apparatus — the 
three-way  glass  tap  between  the  eudiometer  and  laboratory  tube, 
and  the  steel  tap  at  the  lower  ends  of  the  barometer  and  eudiometer. 
The  steel  tap  is  greased  with  a  little  beef-tallow  (made  from  clean 
beef-suet),  or  with  real  Eussian  tallow;  it  will  last  for  twelve 
months  without  further  attention.  A  moderately  thick  washer  of 
india-rubber,  placed  between  the  steel  washer  and  the  nut  at  the 
end  of  the  steel  tap,  adds  greatly  to  the  steady  working  of  the 
needle  on  the  quadrant.  Moderately  soft  resin  cerate  is  best  for 
the  glass  tap. 

When  filling  the  laboratory  vessel  with  mercury,  suction  is 
maintained  until  the  mercury  has  reached  some  height  in  the 
hollow  of  the  three-way  tap.  The  remainder  of  the  hollow  space 
is  replenished  by  pouring  the  mercury  from  a  small  crucible ;  any 
water  that  may  be  present  is  then  removed,  and  the  small  stopper 
inserted.  When  the  laboratory  vessel  has  to  be  washed  out  after 
an  absorption,  the  gas  is  transferred  to  the  eudiometer  until  the 
absorbent  gets  within  a  quarter  of  an  inch  of  the  stop-cock.  The 
mechanical  arrangement  should  be  so  manageable  that  this  nicety 
of  adjustment  can  be  accomplished  with  ease.  Much  depends,  of 
course,  upon  the  care  bestowed  in  cerating  the  tap,  so  that  the 
capillary  is  not  carelessly  blocked  up.  As  soon  as  the  gas  has 
passed  over  to  the  extent  required,  turn  the  three-way  tap  until  the 
through-way  is  at  right  angles  to  the  capillary,  and  the  way  to  the 
hollow  of  the  tap  is  in  communication  with  the  laboratory  vessel, 
then  take  out  the  little  stopper  from  the  hollow,  so  that  the  mercury 
shall  flow  out,  and  allow  the  laboratory  vessel  to  become  emptied 
whilst  the  reading  of  the  volume  of  the  gas  is  being  taken.  The 


§  98. 


THOMAS  S   GAS    APPARATUS. 


513 


best  arrangement  for  washing  out  the  laboratory  tube  is  a  "  syphon 
enema"  (Dr.  Higginson's  principle,  which  may  be  obtained  of 
any  druggist),  adapting  in  the  place  of  the  usual  nozzle  a  bent  glass 
tube.  This  syringe  is  constant  in  its  action,  as  it  fills  itself  when 
the  pressure  is  released,  if  the  tube  at  the  lower  end  is  placed  in 
a  vessel  of  water.  The  laboratory  vessel  can  be  washed  out  and 
refilled  in  a  very  little  time,  as  it  is  already  connected,  and  for  all 
ordinary  absorptions  it  is  sufficient  to  wipe  the  vessel  out  once  by 
passing  up  a  fine  towel  twisted  on  a  round  stick.  When  CnH2n 
gases  are  to  be  absorbed  by  fuming  sulphuric  acid,  the  water  should 
be  carefully  blown  out  of  the  capillary  tube  into  the  laboratory 
vessel,  which  must  be  repeatedly  dried.  A  few  drops  of  strong 
sulphuric  acid  were  at  first  run  into  the  hollow  of  the  tap  and  then 
through  the  capillary  whilst  the  labora- 
tory vessel  was  full  of  mercury,  in  order 
to  remove  any  moisture  remaining,  but 
it  has  since  been  found  unnecessary,  as 
the  drying  can  be  performed  thoroughly 
without. 

To  calibrate  the  eudiometer  with 
water,  introduce  the  quantity  required 
through  the  hollow  in  the  stopper,  then 
remove  the  latter,  and  collect  the  water 
in  a  light  flask  from  the  bottom  of  the 
tap-socket. 

In  the  same  paper  (/.  C.  S.,  May, 
1879),  Thomas  pointed  out  that  it  was 
not  essential  to  add  excess  of  either 
oxygen  or  hydrogen  for  the  purpose  of 
modifying  the  force  of  the  explosion 
when  combustible  gases  were  under 
analysis,  and  it  is  necessary  to  take 
advantage  of  this  when  working  with  so 
short  an  eudiometer.  The  method  is, 
however,  applicable  to  all  gas  apparatus 
having  a  reasonable  length  of  barometer 
column  above  the  eudiometer ;  in  fact, 
the  exploding  pressures  were  first  worked 
out  and  employed  in  an  apparatus  on  Me  Leod's  model.  When  the 
percentage  of  oxygen  in  a  sample  of  air  has  to  be  determined  by 
explosion,  only  one-half  its  volume  of  hydrogen  is  required,  and  the 
pressure  need  not  be  reduced  below  400  m.m.  If  much  more  than 
one-half  volume  of  hydrogen  has  been  added  by  accident,  explode 
under  atmospheric  pressure.  When  the  excess  of  oxygen  used  in  an 
analysis  has  to  be  determined,  add  2*5  times  its  volume  of  hydrogen, 
and  reduce  the  pressure  to  180  m.m.  of  mercury  before  exploding. 
After  adding  the  hydrogen  and  the  reading  has  been  taken,  the  gas 
is  expanded  by  lowering  the  mercurial  reservoir  until  a  column  of 

L  L 


Pig.  88. 


514 


VOLUMETRIC  ANALYSIS. 


§  98. 


mercury,  measuring  the  number  of  m.m.'s  in  length  just  referred  to 
and  in  the  following  table,  stands  above  the  meniscus  of  the  mercury 
in  the  eudiometer.  This  column  can  be  read  off  quite  near  enough  by 
the  eye,  as  there  is  no  risk  of  breaking  the  apparatus  by  the  force  of 
the  explosion  if  the  pressure  is  20  m.m.  greater  than  that  given ; 
but  if  the  gas  under  analysis  is  all  combustible,  it  is  better  to 
explode  at  a  slightly  less  pressure  than  to  exceed  that  recommended. 


«l 

of 

<£             ^ 

Name  of  Gas. 

ill 

111 

ifll 

S^a^5 

CO  '£H    ^  'o. 

jjj 

If 

£a    8 

Hydrogen  - 

1 

200  m.m. 

Carbonic  Oxide  - 

1 

200  m.m. 

Marsh  Gas 

2-5 

170  m.m. 

Acetylene  - 

3 

150  m.m. 

Olefiant  Gas 

3-5 

145  m.m. 

Methyl  and  Hydride  of  Ethyl 

4 

140  m.m. 

Propyl 

1 

5 

135  m.m. 

Hydride  of  Propyl 

1 

5-5 

130  m.m. 

Butyl 

1 

6 

125  m.m. 

Ethyl  and  Hydride  of  Butyl 

1 

7 

120  m.m. 

It  follows,  naturally,  that  the  exploding  pressure  will  depend  upon 
the  proportion  of  combustible  gas  introduced;  and  experience 
alone  can  enable  one  to  determine  with  any  degree  of  exactness 
what  that  pressure  must  be,  as  no  general  law  can  be  laid  down. 
For  instance,  if  more  than  three  volumes  of  hydrogen  were  added 
to  one  of  oxygen,  the  exploding  pressure  should  exceed  200  m.m. ; 
and  if  much  nitrogen  or  other  gas  were  present  that  did  not  take  a 
part  in  the  reaction,  the  pressure  should  be  still  more  increased. 
As  a  consequence,  the  same  experience  is  necessary  when  dealing 
with  explosive  gases  by  the  other  method,  because  the  addition 
of  too  much  inert  gas,  with  a  view  to  modify  the  force  of  the 
explosion,  may  lead  to  imperfect  combustion,  inasmuch  as  the 
cooling  effect  of  the  tube  and  gas  can  reduce  the  temperature 
below  that  required.  In  all  instances,  when  the  approximate  com- 
position of  the  gas  is  known,  it  is  not  difficult  to  determine  the 
quantity  of  oxygen  or  hydrogen,  as  the  case  may  be,  which  is 
required  for  explosion,  or  the  pressure  under  which  the  gas  should 
be  exploded.  In  order  to  do  this  systematically,  it  is  always  well 
to  remember  certain  points  observed  during  the  stages  of  the 
analysis.  The  gas  in  the  laboratory  vessel,  before  being  transferred 
to  the  eudiometer,  occupies  a  certain  volume  in  a  position  between 
(or  otherwise)  the  calibration  divisions.  After  transferring  and 
reading  off,  bear  in  mind  the  number  of  m.m.'s  which  the  volume 


§  98.  REISER'S  GAS  APPARATUS.  515 

represents ;  'and  calculate,  as  tlie  gas  is  being  re-transferred  to  the 
laboratory  vessel  to  be  mixed  with  that  employed  in  the  explosion, 
the  height  at  which  the  mercury  should  stand  in  the  barometer 
tube  when  measuring  the  mixed  gases,  and  how  much  of  the 
laboratory  vessel  was  occupied  on  a  previous  occasion  when  a  similar 
reading  was  obtained.  If  this  is  done,  one  can  realize  at  once,  after 
reading  off  the  volume  of  the  mixed  gases,  the  proportion  of  com- 
bustible gas  added,  and  the  pressure  under  which  the  gas  has  been 
measured.  Another  glance  at  the  volume  which  the  gas  occupies  in 
the  eudiometer,  with  a  comparison  of  the  pressure  recorded  upon 
the  barometer  tube,  enables  one,  after  a  little  practice,  to  at  once 
expand  the  mixture  to  the  point  at  which  it  will  explode  with 
satisfactory  results.  It  is  not  expedient  to  place  too  much  reliance 
upon  the  marks  showing  equal  volumes  upon  the  laboratory  vessel, 
especially  when  dealing  with  small  quantities  of  gas;  and  a 
comparison  of  the  volumes  obtained  in  reading  before  and  after  the 
addition  of  oxygen  or  hydrogen  is  always  prudent,  in  order  to  see 
that  sufficient  gas  has  been  added,  as  well  as  to  enable  one  to  judge 
the  pressure  under  which  the  gas  should  be  exploded. 

NOTE.— Meyer  and  Seubert  (Z.  a.  C.  xxiv.  414)  have  designed  a  gas  apparatus 
similar  in  many  respects  to  that  of  Me  Leod  and  Thomas,  but  of  simpler  con- 
struction, and  especially  adapted  for  explosions  under  diminished  pressure. 


Keiser's   Portable   Gas   Apparatus. 

This  apparatus  is  based  on  the  principle  of  determining  the 
volume  of  a  gas  from  the  weight  of  mercury  which  it  may  be  made 
to  displace  at  a  known  temperature  and  pressure.  It  dispenses 
entirely  with  the  long  graduated  tubes  and  other  vessels  common  to 
the  apparatus  previously  described,  without  any  sacrifice  of  accuracy. 

The  following  description  occurs  in  the  Amer.  CJiem.  Journ.,  1886 
(but  is  reproduced  here  from  The  Analyst,  xi.  106) : — 

Fig.  89  shows  the  construction  of  the  measuring  apparatus  and 
the  absorption  pipette.  A  is  the  measuring  apparatus,  B  is  the 
absorption  pipette;  a  and  b  are  glass  bulbs  of  about  150  c.c. 
capacity.  They  are  connected  at  the  bottom  by  a  glass  tube  of 
1  m.m.  bore,  carrying  the  three-way  stop-cock  d.  The  construction 
of  the  key  of  the  stop-cock  is  shown  in  the  margin.  One  hole  is 
drilled  straight  through  the  key,  and  by  means  of  this  the  vessels  a 
and  b  may  be  made  to  communicate.  Another  opening  is  drilled  at 
right  angles  to  the  first,  which  communicates  with  an  opening 
extending  through  the  handle,  but  does  not  communicate  with  the 
first  opening.  By  means  of  this,  mercury  contained  in  either  a  or  b 
may  be  allowed  to  flow  out  through  the  handle  d  into  a  cup  placed 
beneath.  The  bulb  b  is  contracted  at  the  top  to  an  opening  20  m.m. 
in  diameter.  This  is  closed  by  a  rubber  stopper  carrying  a  bent 
glass  tube,  to  which  is  attached  the  rubber  pump  e.  To  a  second 
glass  tube  passing  through  the  stopper,  a  short  piece  of  rubber 

L  L  2 


516 


VOLUMETRIC  ANALYSIS. 


§    98. 


tubing  with  a  pinch-cock  is  attached.  By  means  of  the  pump  e  air 
may  be  forced  into  or  withdrawn  from  I,  as  one  or  the  other  end  of 
the  pump  is  attached  to  the  glass  tube.  The  bulb  a  terminates  at 
the  top  in  a  narrow  glass  tube,  to  which  is  fused  the  three-way  stop- 
cock c.  The  construc- 
tion of  the  key  of  this 
stop-cock  is  also  shown 
in  the  cut.  By  meanks 
of  it  the  vessel  a  may 
be  allowed  to  com- 
municate with  the 
outside  air,  or  with 
the  tube  passing  to 
the  absorption  pipette,, 
or  with  the  gauge  g» 
The  gauge  g  is  a  glass 
tube  having  a  bore 
1  m.m.  in  diameter 
and  bent,  as  shown  in 
the  figure.  By  pouring 
a  few  drops  of  water 
into  the  open  end  of 
this  tube  a  column  of 


Pig.  89. 


water  several  centimeters  high  in  both  limbs  of  the  tube  is  obtained. 
This  serves  as  a  manometer,  and  enables  the  operator  to  know  when 
the  pressure  of  the  gas  equals  the  atmospheric  pressure.  To  secure 
a  uniform  temperature,  the  bulbs  a  and  b  are  surrounded  by  water 
contained  in  a  glass  vessel.  This  vessel  for  holding  water  is  merely 
an  inverted  bottle  of  clear  glass  from  which  the  bottom  has  been 
removed.  The  handle  of  the  stop-cock  d  passes  through  a  rubber 
stopper  in  the  neck  of  the  bottle.  A  thermometer  graduated  to  i° 
is  placed  in  the  water  near  the  bulb  a.  The  whole  apparatus  is 
supported  upon  a  vertical  wooden  stand. 

The  absorption  pipette  B  consists  of  two  nearly  spherical  glass 
bulbs  of  about  300  c.c.  capacity.  They  communicate  at  the  bottom 
by  means  of  a  glass  tube,  3  m.m.  inside  diameter,  c'  is  a  two-way 
stop-cock.  The  holes  in  the  key  are  drilled  at  right  angles,  so  that 
the  tube  which  connects  with  the  measuring  apparatus  may  be  put 
in  communication  either  with  the  funnel  or  with  the  absorption 
bulb.  The  funnel  is  of  service  in  removing  air  from  the  tube  which 
connects  the  measuring  apparatus  with  the  absorption  pipette.  By 
pouring  mercury  or  water  into  the  funnel  and  turning  the  stop- 
cocks c'  and  c  in  the  proper  directions  all  the  air  is  readily  removed. 
/  is  a  rubber  pump  used  in  transferring  gas  from  B  to  A.  The 
lower  part  of  the  pipette  contains  mercury,  which  protects  the 
reagent  from  the  action  of  the  air. 

To  measure  the  volume  of  a  gas,  the  vessel  a  is  filled  completely 
with  pure  mercury.  This  is  easily  accomplished  by  pouring  the 


§  98.  REISER'S  GAS  APPARATUS.  517 

mercury  into  I,  and  then,  after  turning  c  until  a  communicates  with 
the  outside  air,  forcing  it  into  a  by  means  of  the  pump  e.  Any 
excess  of  mercury  in  b  is  then  allowed  to  flow  out  through  the  stop- 
cock d.  When  a  and  b  are  now  placed  into  communication  the 
mercury  will  flow  from  a  to  b,  and  gas  will  be  drawn  in  through  the 
stop-cock  c.  The  volume  of  mercury  which  flows  into  b  is  equal  to 
the  volume  of  gas  drawn  into  a.  When  the  mercury  no  longer 
rises  in  b,  and  it  is  desired  to  draw  in  still  more  gas  into  a,  then  it 
is  only  necessary  to  exhaust  the  air  in  b  by  means  of  the  pump  e. 
After  the  desired  quantity  of  gas  has  been  drawn  into  a  the  stop- 
cock c  is  closed.  After  standing  a  few  minutes  the  temperature  of 
the  gas  becomes  the  same  as  that  of  the  water  surrounding  a. 
The  pressure  of  the  gas  is  then  made  approximately  equal  to  atmos- 
pheric pressure  by  allowing  the  mercury  to  flow  out  of  b  into  a 
weighed  beaker  placed  beneath  the  stop-cock  d  until  it  stands  at 
nearly  the  same  level  in  both  a  and  b.  Communication  is  now 
established  between  a  and  g,  and  by  means  of  the  pump  e  the 
pressure  can  be  adjusted  with  the  utmost  delicacy  until  it  is  exactly 
equal  to  atmospheric  pressure.  The  stop-cock  d  is  then  closed,  and 
the  remainder  of  the  mercury  in  b  is  allowed  to  flow  out  into  the 
beaker.  The  weight  of  the  mercury  displaced  by  the  gas  divided 
by  the  specific  gravity  of  mercury  at  the  observed  temperature  gives 
the  volume  of  the  gas  in  cubic  centimeters. 

If  it  is  desired  to  remove  any  constituent  of  the  gas  by  absorption, 
a  pipette  B,  containing  the  appropriate  reagent,  is  attached  to  the 
measuring  apparatus.  All  the  air  in  the  connecting  tube  is  expelled 
by  pouring  mercury  into  the  funnel  and  turning  the  stop-cocks 
c'  and  c  so  that  the  mercury  flows  out  through  c.  A  little  more 
than  enough  mercury  to  expel  the  gas  in  the  vessel  a  is  poured  into  b. 
The  small  quantity  of  air  which  is  confined  in  the  tube  connecting  b 
with  the  stop-cock  is  removed  by  allowing  a  few  drops  of  mercury 
to  run  out  through  b.  Then  a  and  b  are  placed  in  communication. 
The  stop-cocks  c'  and  c  are  turned  so  that  the  gas  may  pass  into  the 
pipette,  the  mercury  which  filled  the  connecting  tube  passes  into  the 
absorbing  reagent  and  unites  with  that  which  is  already  at  the 
bottom  of  the  pipette.  The  transfer  is  facilitated  by  the  pump  e. 
After  absorption  the  residual  volume  is  measured  in  the  same  way 
that  the  original  volume  was  measured,  a  is  completely  filled  with 
mercury  from  the  upper  to  the  lower  stop-cock,  and  all  the  mercury 
in  b  is  allowed  to  run  out ;  the  gas  is  then  drawn  back  into  the 
measuring  apparatus,  the  last  portion  remaining  in  the  connecting- 
tube  being  displaced  by  means  of  mercury  from  the  funnel.  The 
volume  is  then  determined  as  before. 

The  calculation  of  the  results  of  an  analysis  is  very  simple.  If 
the  temperature  and  pressure  remain  the  same  during  an  analysis,  as 
is  frequently  the  case,  then  the  weights  of  mercury  obtained  are  in 
direct  proportion  to  the  gas  volumes,  and  the  percentage  composition 
is  at  once  obtained  by  a  simple  proportion. 


518  VOLUMETKIC  ANALYSIS.  §    98. 

If  the  temperature  and  pressure  are  different  when  the 
measurements  are  made,  it  is  necessary  to  reduce  the  volumes  to 
0°  and  760  m.m.  The  following  formula  is  then  used : — 

W(H-h) 

~  D(l+  0-00367  xt)  760' 
in  which 

W=  weight  of  mercury  obtained  (in  grams), 
D  =  specific  gravity  of  mercury  at  t°, 

t  —  temperature  at  which  the  gas  is  measured, 
H=  height  of  the  barometer, 
h  =  tension  of  aqueous  vapour, 
V  =  reduced  gas  volume  (in  cubic  centimeters). 
In  all  the  measurements  made  with  the  apparatus  the  gas  is 
saturated  with  aqueous  vapour,  because  it  comes  in  contact  with 
the  water  in  the  manometer  cj. 

The  following  experiments  were  made  to  test  the  accuracy  of  the 
instrument.  A  quantity  of  air  was  drawn  into  the  measuring  bulb 
and  its  volume  determined.  The  air  was  then  transferred  to  an 
absorption  pipette  which  contained  only  mercury  and  no  reagent. 
It  was  then  brought  back  again  into  the  measuring  apparatus  and 
its  volume  redetermined.  The  following  results  were  obtained  : — 

I. 

Volume  at  0°— 760  in.m. 
Volume  of  air  taken        ...  ...  ...  5V  558  c.c. 

after  first  transfer  ...  57'567 

„          „     second  transfer         ...  ...  57' 570 

II. 

At  0°— 760  m.m. 
Volume  taken    ...  ...  ...  ...  93'216  c.c. 

„        after  transferring  ...  93'229 

III. 

At  0°— 760  m.m. 
Volume  taken    ...  ...  ...  ...          133'473  c.c. 

after  transferring  ...  133-490 

IV. 

At  0°— 760  m.rn. 
Volume  taken    ...  ...  ...  ...  92'275  c.c. 

„       after  transferring  ...  ...  92'260 

V. 

At  0°— 760  m.m. 
Volume  taken    ...  ...  ...  ...          109-025  c.c. 

„       after  transferring  ...  ...          109'020 

VI. 

At  0°— 760  m.m. 
Volume  taken    ...  ...  ...  ...  103*970  c.c. 

„        after  first  transfer  ...  ...  103*955 

„          „     second  transfer    "     ...  ...          103'980 

The  apparatus  was  also  tested  by  making  analyses  of  atmospheric 
air.     It  has  been  shown  both  by  Winkler  and  Hemp  el  that  the 


§    99.  SIMPLER  METHODS   OF   GAS  ANALYSIS. 

composition  of  the  air  varies  from  day  to  day.  This  variation  is 
sometimes  as  much  as  0'5  per  cent.  The  causes  which  produce 
these  fluctuations  in  the  composition  of  the  atmosphere  are  at 
present  but  imperfectly  understood.  It  is  therefore  desirable  to 
have  some  simple  instrument  by  means  of  which  the  composition 
of  the  air  may  be  determined  rapidly  and  yet  with  great  accuracy. 
The  following  analyses  show  that  the  apparatus  here  described 
is  well  adapted  to  this  purpose.  The  reagent  used  to  absorb  the 
oxygen  and  carbon  dioxide  was  an  alkaline  solution  of  pyrogallol, 
prepared  by  mixing  one  volume  of  a  25  per  cent,  solution  of 
pyrogallol  with  six  volumes  of  a  60  per  cent,  solution  of  potassic 
hydrate. 

Analysis  of  Air  taken  from  the  Laboratory. 

1. 

Per  cent. 

W  H  t  V  O+CO2. 

Air  taken  1738-53        743*37        15*8        116'435  c.c. 

Vol.  of  nitrogen  1377*62  743*37  15*8  92*264  20760 
1376-40  743-55  1575  92'255  20771 
Per  cent,  of  O  and  CO2,  20*765. 

II. 

Per  cent. 

W  H  t  V  O+CO2. 

Yol.  of  air  1708'01        748*08        15'0        115*546  c.c.       ... 

nitrogen  1356*04        747*33        15*2          91'564        20*755 
Per  cent,  of  O  and  CO2  found,  20*755. 

The  following  analyses  were  made  with  a  sample  of  atmospheric  air 
collected  on  a  subsequent  day : — 

Per  cent. 

W  H  t  V  O+CO2. 

Yol.  of  air  1704*81        754*92        12*2        117*814  c.c. 

„  nitrogen  1348*33  754*78  12*08  93*216  20'877 
1344*71  755*92  11*7  93*229  20*868 
Per  cent,  of  O  and  CO2,  20*872. 

II. 

Per  cent. 

W  H  t  V  O+CO2. 

Vol.  of  air  1669*39        756*30        10*15      116*584  c.c. 

nitrogen  1323*24  755*49  10*05  92*260  20*863 
1322*38  755*30  10*00  92*252  20*870 
Per  cent,  of  O  and  CO2,  20*866. 

The  apparatus  described  in  the  preceding  pages  was  made  for  the  author, 
in  most  excellent  manner,  by  Mr.  Emil  Griener,  79,  Nassau  Street,  New  York. 


SIMPLER    METHODS    OF    GAS    ANALYSIS. 

§  99.  ALL  the  sets  of  apparatus  previously  described  are  adapted 
to  secure  the  greatest  amount  of  accuracy,  regardless  of  speed  or  the 
time  occupied  in  carrying  out  the  various  intricate  processes  involved. 

For  industrial  and  technical  purposes  the  demand  for  something 


520  VOLUMETRIC  ANALYSIS.  §    99. 

requiring  less  time  and  care,  even  at  the  sacrifice  of  some  accuracy, 
has  been  met  by  a  large  number  of  designs  for  apparatus  of  a 
simpler  class,  among  which  may  be  mentioned  those  of  Or  sat, 
Bunte,  Winkel,  Hempel,  Stead,  Lunge,  etc.  Many  of  these 
are  arranged  to  suit  the  convenience  of  special  industries,  and  will 
not  be  described  here. 

The  most  useful  apparatus  for  general  purposes  is  either  that  of 
Hempel  or  Lunge,  both  of  which  will  be  shortly  described. 
Fuller  details  as  to  these  and  other  special  kinds  of  apparatus  are 
contained  in  Winkler's  Handbook  of  Technical  Gas  Analysis, 
translated  by  Lunge.* 

The  general  principles  upon  which  these  various  sets  of  apparatus 
are  based,  and  the  calculation  of  results,  are  the  same  as  have  been 
described  in  preceding  pages ;  and  of  course  due  regard  must  be 
had  to  tolerable  equality  of  temperature  and  pressure,  and  the  effects 
of  cold  or  warm  draughts  of  air  upon  the  apparatus  whilst  the 
manipulations  are  carried  on.  If  the  operator  is  not  already 
familiar  with  methods  of  gas  analysis,  a  study  of  the  foregoing 
sections  will  be  of  great  assistance  in  manipulating  the  apparatus 
now  to  be  described. 

Simple  Titration  of  Gases. — Many  instances  occur  in  which  an 
absorbable  gas  can  be  passed  through  a  solution  of  known  standard 
in  excess,  and  the  measure  of  the  gas  being  known  either  by 
emptying  an  aspirator  of  water  containing  a  known  volume,  or  by 
the  use  of  a  gas-meter.  The  amount  of  gas  absorbed  may  be  found 
by  titration  of  the  standard  absorbent  residually.  Such  instances 
occur  in  the  exit  gases  of  vitriol  and  chlorine  chambers.  In  the  case 
of  vitriol  exits  the  gases  are  drawn  through  a  standard  solution  of 
soda  or  other  alkali  contained  in  Todd's  absorption  tubes  or  some 
similar  arrangement,  to  which  is  attached  a  vessel  containing  a 
known  volume,  say  exactly  -^  of  a  cubic  foot  of  water.  A  tap  is 
fixed  at  the  bottom  of  this  vessel,  so  that  when  all  is  tightly  fitted 
and  the  tap  partially  opened,  a  small  flow  of  water  is  induced, 
which  draws  the  gases  through  the  absorbent.  When  the  aspirator 
is  empty  the  flow  of  gases  ceases,  and  of  course  the  volume  of 
water  so  run  out  represents  that  of  the  gases  passed. 

Another  way  of  measuring  the  gases  is  to  use  an  india-rubber 
vessel,  which  can  be  compressed  by  the  hand,  known  as  a  finger- 
pump.  The  volume  contents  being  known  by  measurement  with 
water  or  air,  the  aspirations  made  by  it  may  be  calculated;  the 
aspirated  gases  are  then  drawn  slowly  through  the  absorbent  liquid. 
In  the  case  of  chlorine  exits  the  gases  are  passed  through  a  solution 
of  potassic  iodide  in  excess,  and  the  amount  of  liberated  iodine 
subsequently  found  by  titration  with  standard  sodic  arsenite.  A 
most  convenient  vessel  is  the  revolving  double  glass  aspirator, 
known  as  Dancer's,  or  Muencke's. 

*  Van  Voorst,  1885. 


§    99.  NORMAL   SOLUTIONS   FOR   GAS   ANALYSIS.  521 

The  standard  solutions  used  in  these  cases  are  generally  so 
arranged  as  to  avoid  calculations,  and  the  result  found  for  legal 
purposes  in  England  is  given  in  grains  per  cubic  foot,  in  order  to 
comply  with  the  conditions  of  the  Noxious  Vapours  Act,  which 
enjoins  that  not  more  than  4  grains  of  SO3,  or  2J  grains  of  Cl,  in 
one  cubic  foot  shall  be  allowed  to  pass  into  the  atmosphere. 

Sometimes  a  gas  may  be  estimated  by  the  reaction  which  takes 
place  when  brought  in  contact  with  a  chemical  absorbent,  such  as 
the  formation  of  a  precipitate,  or  the  change  of  colour  which  it 
produces  in  an  indicator.  The  gas  in  this  case  can  be  measured 
by  a  graduated  aspirator,  the  flow  of  which  is  stopped  when  the 
peculiar  reaction  ceases  or  is  manifested. 

Normal  Solutions  for  Gas  Analysis. — In  the  titratioil  of  gases  by 
these  methods,  particularly  on  the  Continent,  the  custom  is  to  use 
special  normal  solutions,  1  c.c.  of  which  represents  1  c.c.  of  the 
absorbable  gas  in  a  dry  condition,  and  at  760  m.m.  pressure  and 
0°C.  temperature.  These  solutions  must  not  be  confounded  with 
the  usual  normal  solutions  used  in  volumetric  analysis  of  liquids  or 
solids.  For  instance,  a  normal  gas  solution  for  chlorine  would  be 
made  by  dissolving  4 '4288  gm.  of  As203,  with  a  few  grams  of  sodic 
bicarbonate  to  the  liter,  and  a  corresponding  solution  of  iodine 
containing  11*3396  gm.  per  liter,  in  order  that  1  c.c.  of  either 
should  correspond  to  1  c.c.  of  chlorine  gas.  1  c.c.  of  the  same 
iodine  solution  would  also  represent  1  c.c.  of  dry  SO2,  and  so  on. 

A  very  convenient  bottle  for  the  titration  of  certain  gases  is 
adopted  by  Hesse.  It  is  made  in  a  conical  form,  like  an 
Erlenmeyer's  flask,  and  has  a  mark  in  the  short  neck,  down  to 
which  is  exactly  fitted  a  caoutchouc  stopper  having  two  holes, 
which  will  either  admit  the  spit  of  a  burette  or  pipette,  or  may  be 
securely  closed  by  solid  glass  rods.  The  exact  contents  of  the  vessel 
up  to  the  stopper  is  ascertained,  and  a  convenient  size  is  about  500 
or  600  c.c.  The  exact  volume  is  marked  upon  the  vessel. 

In  the  case  of  gases  not  affected  by  water,  the  bottle  is  filled  with 
that  liquid  and  a  portion  displaced  by  the  gas,  and  the  stopper  with 
its  closed  holes  inserted.  If  water  cannot  be  used,  the  gas  is  drawn 
into  the  empty  bottle  by  means  of  tubes  with  an  elastic  pump. 
The  absorbable  contituent  of  the  gas  is  then  estimated  with  an 
excess  of  the  standard  solution  run  in  from  a  pipette  or  burette. 
During  this  a  volume  of  the  gas  escapes  equal  to  the  volume  of 
standard  solution  added,  which  must  of  course  be  deducted  from 
the  contents  of  the  absorbing  vessel.  The  gas  and  liquid  are  left  to 
react  with  gentle  shaking  until  complete.  The  excess  of  standard 
solution  is  then  found  residually  by  another  corresponding  standard 
solution;  and  in  the  case  of  using  gas  normal  solutions,  the  difference 
found  corresponds  to  the  volume  of  the  absorbed  constituent  of  the 
gas  in  c.c. ;  and  from  this,  and  from  the  total  volume  of  gas  employed, 
may  be  calculated  the  percentage,  allowing  for  the  correction  men- 


522 


VOLUMETRIC   ANALYSIS. 


99. 


tioned.  This  arrangement  may  be  used  for  CO2  in  air,  using  normal 
gas  baric  hydrate  and  a  corresponding  normal  gas  oxalic  acid  with 
phenolphthalein.  The  normal  oxalic  acid  should  contain  5 '63 14  gm. 
per  liter,  in  order  that  1  c.c.  may  represent  1  c.c.  of  CO2.  The  baryta 
solution  must  correspond,  or  its  relation  thereto  found  by  blank 
experiment  at  the  time.  The  arrangement  is  also  available  for  HC1 
in  gases,  using  a  normal  gas  silver  solution  containing  4 '8233  gm. 
Ag  per  liter,  as  absorbent,  with  a  corresponding  solution  of 
thiocyanate  (§  39)  and  ferric  indicator;  or  the  HC1  may  be  absorbed 
by  potash,  then  acidified  with  HIST03, 
and  the  titration  carried  out  by  the 
same  process ;  or  again,  an  alkaline- 
carbonate  may  be  used,  and  the  titration 
made  with  a  normal  gas  silver  solution 
using  the  chromate  indicator  .(§  37,  2/>). 

Hem  pel's  G-as  Burette. -This  consists 
of  two  tubes  of  glass  on  feet,  one  of  which 


is  graduated  to  100  c.c.  in 


(the 


burette  proper),  and  the  other  plain  (the 
level  tube).  They  are  connected  at  the 
feet  by  an  elastic  tube,  much  in  the 
same  way  as  Lunge's  nitrometer.  The 
arrangement  is  shown  in  fig.  90. 

The  illustration  shows  the  burette  with 
three-way  stop-cock  at  bottom,  which  is 
necessary  in  the  case  of  gases  soluble  in 
water,  or  where  any  of  the  constituents 
are  affected  thereby.  If  this  is  not  the 
case,  a  burette  without  such  stop-cock 
is  substituted  (fig.  91).  The  elastic  tube 
should  not  be  in  one  piece,  but  con- 
nected in  the  middle  by  a  short  length 
of  glass  tube  to  admit  of  ready  dis- 
connection. 

Fig.  91  will  illustrate  not  only  the  original  Hemp  el  burette 
with  level  tube,  but  also  the  method  of  connection  with  the  gas 
pipette,  and  also  the  way  in  which  the  elastic  tube  is  joined  by  the 
intervening  glass  tube.* 

Hemp  el,  with  great  ingenuity,  has  devised  special  pipettes  to 
be  used  in  connection  with  the  burette,  and  which  render  the 
instrument  very  serviceable  for  general  gas  analysis.  The  pipette 

*  The  same  chemist  has  since  designed  a  gas  burette  which  has  the  advantage  of 
"being  unaffected  by  the  fluctuating  temperature  and  pressure  of  the  atmosphere.  This 
is  effected  by  connecting  the  measuring  apparatus  with  a  space  free  from  air,  but 
saturated  with  aqueous  vapour.  A  figure  showing  the  arrangement  is  given  in 
C.  N.  Ivi.  254.  These  simpler  forms  of  gas  apparatus  in  great  variety,  including  various 
forms  of  the  nitrometer,  are  kept  in  stock  by  Messrs.  Townson  and  Mercer,  89  Bishops- 
gate  Street  Within,  London,  E.C.,  and  probably  by  most  of  the  dealers  in  apparatus  in 
the  kingdom. 


Tig.  90. 


§  99. 


HEMPELS   BURETTE  AND  PIPETTES. 


523 


shown  in  fig.  91  is  known  as  the  simple  absorption  pipette,  and 
serves  for  submitting  the  gas  originally  in  the  burette  to  the  action 
of  some  special  absorbent.  With  a  series  of  these  pipettes  the  gas 
is  submitted  to  the  action  of  special  absorbents,  one  after  another, 
until  the  entire  composition  is  ascertained.  The  connections  must 
in  all  cases  be  made  of  best  stout  rubber,  and  bound  with  wire. 


Kg.  91. 

Collection  and  measurement  of  the  Gas  over  "Water. — Both  tubes 
are  filled  completely  with  water  (preferably  already  saturated 
mechanically  with  the  gas),  care  being  taken  that  all  air  is  driven 
out  of  the  elastic  tube.  The  clip  is  then  closed  at  the  top  of  the 
burette,  and  the  bulk  of  the  water  poured  out  of  the  level  tube,  the 


524 


VOLUMETRIC   ANALYSIS. 


§    99. 


elastic  tube  being  pinched  meanwhile  with  the  finger  and  thumb  to 
prevent  air  entering  the  burette.  The  latter  is  then  connected  by 
a  small  glass  tube  with  the  source  of  the  gas  to  be  examined,  when, 
by  lowering  the  level  tube,  the  gas  flows  in  and  displaces  the  water 
from  the  burette  into  the  level  tube.  The  pressure  is  then  regulated 
by  raising  or  lowering  either  of  the  tubes  until  both  are  level,  when 
the  volume  of  gas  is  read  off.  It  is  convenient  of  course  to  take 
exactly  100  c.c.  of  gas  to  save  calculation. 

Collection  and  measurement  of  the  Gas  without  Water. — In  this 
case  the  three-way  tap  burette  (fig.  90)  is  dried  thoroughly  by  first 
washing  with  alcohol,  then  ether,  and  drawing  air  through  it.  The 
three-way  tap  is  then  closed,  the  upper  tube  connected  with  the  gas 
supply,  and  the  burette  filled  either  by  the  pressure  of  the  gas,  or 
by  using  a  small  pump  attached  to  the  three-way  cock  to  draw  out 
the  air  and  fill  the  burette  with  the  gas.  When  full  the  taps  are 
turned  off,  and  connection  made  with  the  level  tube,  which  is  then 
filled  with  water,  the  tap  opened  so  that  the  water  may  flow  into 
the  burette  and  absorb  the  soluble  gases  present.  As  the  burette 
holds  exactly  100  c.c.  between  the  three-way  tap  and  the  upper  clip, 
the  percentage  of  soluble  gas  is  shown  directly  on  the  graduation. 

The  method  of  Absorption. — In  the  case  of  the  simple  pipette 
fig.  91,  a  is  filled  with  the  absorbing  liquid,  which  reaches  into  the 
syphon,  bend  of  the  capillary  tube :  the  bulb  b  remains  nearly 
empty.  In  order  to  fill  the  instrument,  the  liquid  is  poured  into  b, 
and  the  air  sucked  out  of  a  by  the  capillary  tube.  It  is  convenient 
to  keep  a  number  of  these  pipettes  filled  with  various  absorbents, 
well  corked,  and  labelled. 

Another  pipette  of  similar  char- 
acter is  shown  in  fig.  92,  and  is 
adapted  for  solid  reagents,  such  as 
stick  phosphorus  in  water.  The 
instrument  has  an  opening  at  the 
bottom,  which  can  be  closed  with 
a  caoutchouc  stopper.  This  pipette 
is  also  used  for  absorbing  CO2  by 
filling  it  with  plugs  of  wire  gauze 
and  caustic  potash  solution,  so  as 
to  expose  a  large  active  surface 
when  the  liquid  is  displaced  by 
the  gas. 

To  make  an  absorption,  the 
capillary  U-tube  is  connected  with 
the  burette  containing  the  mea- 
sured gas  by  the  small  capillary 


Fig.  92. 


tube  E  (fig.  91),  the  pinchcock  of  course  being  open,  then  by  raising 
the  level  tube,  the  gas  is  driven  over  into  a,  where  it  displaces 
a  portion  of  the  liquid  into  b.  When  the  whole  of  the  gas  is 


§  99.  HEMPEL'S  PIPETTES.  525 

transferred,  the  pinchcock  is  closed,  and  the  absorption  promoted 
by  shaking  the  gas  with  the  reagent.  When  the  action  is  ended, 
communication  with  the  burette  is  restored,  and  the  gas  syphoned 
back  with  the  level  tube  into  the  burette  to  be  measured. 

The  Compound  Gas  Pipette  shown  in  fig.  93  is  of  great  utility  in 
preserving  absorbents  which  would  be  acted  on  by  the  air,  such  for 
instance  as  alkaline  pyrogallol,  cuprous  chloride,  etc.  The  bulb 
next  the  syphon  tube  is  filled  with  the  absorbent,  the  next  is  empty, 
the  third  contains  water,  and  the  fourth  is  empty.  When  the  gas 
is  passed  in,  the  intermediate  water  passes  on  to  the  last  bulb 
to  make  room  for  the  gas,  thus  shutting  off  all  contact  with  the 
atmosphere,  except  the  small  amount  in  the  second  bulb. 

Hydrogen  Pipette. — The  hydrogen  gas  necessary  for  explosions 
or  combustions  is  produced  from  a  hollow  rod  of  zinc  fixed  over 
a  glass  rod  passed  through  the  rubber  stopper  (fig.  92).  The  bulb 
being  filled  with  dilute  acid,  gas  is  generated,  and  as  it  accumulates 
the  acid  is  driven  into  the  next  bulb  and  the  action  ceases. 

Explosion  Pipette. — Another  arrangement  provides  for  explosions 
by  the  introduction  into  a  thicker  bulb,  measured  volumes  of  the 
gas,  of  air,  and  of  hydrogen.  The  bulb  being  shut  off  with 
a  stop-cock,  a  spark  is  passed  through  wires  sealed  into  the  upper 
portion  of  the  bulb. 

Pipette  with  Capillary  Combustion  Tube. — This  simple  arrange- 
ment consists  of  a  short  glass  capillary  tube  bent  at  each  end  in 
a  right  angle,  into  which  an  asbestos  fibre  impregnated  with  finely 
divided  palladium  is  placed,  so  as  to  allow  of  the  passage  of  the  gas.* 
The  gas  being  mixed  with  a  definite  volume  of  air  in  the  burette, 
and  the  measure  ascertained  (not  more  than  25  c.c.  of  gas  and  60 
or  70  c.c.  of  air),  the  asbestos  tube  is  heated  gently  with  a  small  gas 
flame  or  spirit  lamp,  and  the  pinchcocks  being  opened,  the  mixture 
is  slowly  passed  through  the  asbestos  and  back  again,  the  operation 
being  repeated  so  long  as  any  combustible  gas  remains.  No 

*  To  prepare  palladium  asbestos,  dissolve  about  1  gm.  palladium  in  a.qua  regia, 
evaporate  to  dryness  on  water  bath  to  expel  all  acid.  Dissolve  in  a  very  small  quantity 
of  water,  and  add  5  or  6  c.c.  of  saturated  solution  of  sodic  formate,  then  sodic  carbonate 
until  strongly  alkaline.  Introduce  into  the  liquid  about  1  gm.  soft,  long-fibred  asbestos, 
which  should  absorb  the  whole  liquid.  The  fibre  is  then  dried  at  a  gentle  heat,  and 
finally  in  the  water  bath  till  perfectly  dry ;  it  is  then  soaked  in  a  little  warm  water,  put 
into  a  glass  funnel,  and  all  adhering  salts  washed  out  carefully  without  disturbing  the 
palladium  deposit.  The  asbestos  so  prepared  contains  about  50  per  cent.  Pd,  and  in 
a  perfectly  dry  state  is  capable  of  causintr  the  combination  of  H  and  O  at  ordinary 
temperature,  but  when  used  in  the  capillary  tube  it  is  preferable  to  use  heat,  as  mentioned. 
The  capillary  combustion  tubes  are  about  1  m.m.  bore  and  5  m.m.  outside  diameter, 
with  a  length  of  about  15  c.m.  The  fibre  is  placed  into  them  before  bendintr  the  angles 
as  follows : — Lay  a  few  loose  fibres,  about  4  c.m.  long,  side  by  side  on  smooth  filter  paper, 
moisten  with  a  drop  or  two  of  water,  then  by  sliding  the  finger  over  them  t wished  into 
a  kind  of  thread  about  the  thickness  of  fiarning  cotton.  The  thread  is  taken  carefully 
up  with  pincers  and  dropped  into  the  tube  held  vertically,  then  by  id  of  water  a  <i  grentle 
shaking  moved  into  position  in  the  middle  of  the  tube.  The  tube  is  'hen  dried  in  a 
warm  place,  and  finally  the  ends  bent  at  right  angle  for  a  length  of  3;  to  4  c.m. 
Platinum  asbestos  may  be  prepared  in  the  same  way.  using,  however,  only  from  balf  to 
one-fourth  the  quantity  of  metal. 


526  VOLUMETRIC   ANALYSIS.  §    99. 

explosion  need  be  feared.  The  residue  of  gas  ultimately  obtained 
is  then  measured,  and  the  contraction  found ;  from  this  the  volume 
of  gas  burned  is  ascertained  either  directly,  or  by  the  previous 
removal  of  CO2  formed  by  the  combustion  with  the  potash  pipette. 
H  is  very  easily  burned,  CO  less  easily.  Ethylene,  benzine,  and 
acetylene  require  a  greater  heat  and  longer  time.  CH4  is  not 
affected  by  the  method,  even  though  mixed  with  a  large  excess  of 
combustible  gases. 


Fig.  93. 

In  order  to  illustrate  the  working  of  the  whole  set  of  apparatus,  the 
analysis  of  a  mixture  containing  most  or  all  of  the  gases  likely  to  be  met 
with  in  actual  testing  is  given  from  a  paper  contributed  by  Dr.  "W.  Bott 
(J.  8.  C.  I.  iv.  163).  The  mixture  of  gases  consists  of  CO2,  O,  CO,  C2H4, 
CH4,  H  and  N.  A  sample  of  this  gas — say  100  c.c. — is  collected  and 
measured  in  the  gas  burette.  The  CO'-'  is  next  absorbed  by  passing  the  gas 
into  a  pipette  (fig.  91)  containing  a  solution  of  1  part  of  KHO  in 
2  parts  of  water.  To  ensure  a  more  rapid  absorption,  the  bulb  shown 
in  fig.  92  containing  the  caustic  potash  may  be  partly  filled  with  plugs 
of  wire  gauze.  The  absorption  of  the  CO2  is  almost  instantaneous.  It  is 
only  necessary  to  pass  the  gas  into  the  apparatus  and  syphon  it  back  again 
to  be  measured.  The  contraction  produced  gives  directly  the  percentage 
of  CO2,  since  100  c.c.  were  used  at  starting.  The  remaining  gas  contains 
O,  CO,  H,  C2H4,  CH4,  N.  The  oxygen  is  next  absorbed.  This  may  be 
effected  in  two  ways—by  means  of  moist  phosphorus  or  by  an  alkaline 
solution  of  pyrogallic  acid.  The  former  method  is  by  far  the  more  elegant  of 
the  two,  but  not  universally  applicable.  The  absorption  is  done  in  a  pipette 
(fig.  92),  the  corked  bulb  of  which  is  filled  with  thin  sticks  of  yellow  phosphorus 
surrounded  by  water.  The  gas  to  be  tested  is  introduced  in  the  usual  manner, 
and  by  displacing  the  water  comes  into  contact  with  the  moist  surface  of  the 
phosphorus,  which  speedily  absorbs  all  the  oxygen  from  it.  The  absorption 
proceeds  best  at  about  15—20°  C.,  and  is  complete  in  ten  minutes.  The  small 
quantity  of  P2O3  formed  by  the  absorption  dissolves  in  the  water  present,  and 
thus  the  surface  of  the  phosphorus  always  remains  bright  and  active.  This 
neat  and  accurate  method  is  not  however  universally  applicable ;  the  following- 
are  the  conditions  under  which  it  can  be  used :— The  oxygen  in  the  gas  must 


HUBERT  DYER 

§  99.  HEMPEL'S  METHODS  OF  GAS  ANALYSIS.  527 

not  be  more  than  50  per  cent.,  and  the  gas  must  be  free  from  ammonia,  C2H4 
and  other  hydrocarbons,  vapour  of  alcohol,  ether  and  essential  oils.  In  the 
instance  chosen,  the  phosphorus  method  would  hence  not  be  applicable,  as  the 
mixture  contains  C2£L4 ;  therefore  pyrogallic  acid  must  be  used.  The  absorption 
is  carried  out  in  the  compound  absorption  pipette  (fig.  93),  the  bulb  of  which 
is  completely  filled  with  an  alkaline  solution  of  pyrogallol  made  by  dissolving' 
1  part  (by  volume)  of  a  25  per  cent,  pyrogallic  acid  solution  in  6  parts  of  a 
60  per  cent,  solution  of  caustic  potash.  The  absorption  is  complete  in  about 
five  minutes,  but  may  be  hastened  by  shaking.  The  remainder  of  the  gas 
now  contains  C2H4,  CO,  CH4,  H,  N,  and  the  next  step  is  to  absorb  the  C2H4  by 
means  of  fuming  SO3,  the  CH4  being  subsequently  determined  by  explosion. 
In  choosing  the  latter  method  a  portion,  say  half,  of  the  residual  gas  is  taken  for 
the  estimation  of  hydrogen.  The  absorption  of  the  hydrogen  is  based  on  the  fact 
that  palladium  black  is  capable  of  completely  burning  hydrogen  when  mixed 
with  excess  of  air,  and  slowly  passed  over  the  metal  at  the  ordinary  tempera- 
ture. About  H  gni.  of  palladium  black  are  placed  in  a  small  U-tube  plunged 
into  a  small  beaker  of  cold  water,  and  the  gas,  mixed  with  an  excess  of  air 
(which,  of  course,  must  be  accurately  measured),  is  passed  slowly  through  the 
tube  two  or  three  times,*  the  tube  at  the  time  being  connected  with  an 
ordinary  absorption  pipette  filled  with  water  or  else  with  the  KOH  pipette, 
which  in  this  case,  of  course,  simply  serves  as  a  kind  of  receiver.  Finally  the 
gas  is  syphoned  back  into  the  burette  and  measured — two-thirds  of  the  con- 
traction correspond  to  the  amount  of  H  originally  present  in  the  mixture  of 
gas  and  air.  The  CH4  is  not  attacked  by  ordinary  30  per  cent.  SO3  Nordhausen 
acid  during  the  absorption  of  the  C2H4.  The  acid  is  contained  in  an 
absorption  pipette  (fig.  92),  the  bulb  of  which  is  filled  with  pieces  of 
broken  glass  so  as  to  offer  a  larger  absorbing  surface  to  the  gas.  The 
absorption  is  complete  in  a  few  minutes,  but  the  remaining  gas  previous  to 
measuring  should  be  passed  into  the  KOH  pipette  and  back  again,  so  as  to 
free  it  from  fumes  of  SO3.  Residual  gas :  CO,  CH4,  H,  N.  The  CO  is  next 
absorbed  by  means  of  an  ammoniacal  solution  of  cuprous  chloride  in  a  com- 
pound absorption  pipette.  The  gas  has  to  be  shaken  with  the  absorbent  for 
about  three  minutes.  It  must  be  borne  in  mind  that  Cu2Cl2  solution  also 
absorbs  oxygen,  and,  according  to  Hempel,  considerable  quantities  of  C2H4, 
hence  these  gases  must  be  removed  previously.  Residue :  CH4,  H,  N.  Both 
CH4  and  H  may  now  be  estimated  either  by  exploding  with  an  excess  of  air 
in  the  explosion  pipette  and  measuring  (1)  the  contraction  produced,  and  (2) 
the  amount  of  CO2  formed  (by  means  of  the  KOH  pipette) ;  or,  according  to 
Hempel,  absorb  the  hydrogen  first  of  all  as  described  above— provided  the 
TJ-tube  be  kept  well  cooled  with  water,  inasmuch  as  that  at  about  200°  C.  a 
mixture  of  air  and  CH4  is  also  acted  upon  by  palladium.  The  presence  of 
CO,  vapours  of  alcohol,  benzine  and  hydrochloric  acid  also  interfere  with 
the  absorption  by  palladium. 

The  palladium  may  be  used  for  many  consecutive  experiments,  but  must 
be  kept  as  dry  as  possible.  After  it  has  been  used  for  several  absorptions  it 
may  be  regenerated  by  plunging  the  tube  into  hot  water  and  passing  a 
current  of  dry  air  through  it. 

Having  estimated  the  hydrogen,  the  CH4  in  the  remaining  portion  of  the 
gas  has  to  be  determined.  This  contains  CH4,  N  and  H,  the  amount  of  the 
latter  being  known  from  the  previous  experiment.  The  gas  is  mixed  with  the 
requisite  quantity  of  air  and  hydrogen,  introduced  into  the  explosion  pipette 
and  fired  by  means  of  a  spark.  The  water  resulting  from  the  combustion 
condenses  in  the  bulb  of  the  pipette,  whilst  the  CO2  formed  is  absorbed  by  the 
KOH  solution  present.  Hence  the  total  contraction  produced  corresponds  to : 

«.  The  hydrogen  present  in  the  original  gas  +  i  its  vol.  of  O  (the  quantity 
requisite  for  complete  combustion). 

*  Instead  of  this  the  H  may  be  burned  in  the  tube  containing  the  palladium  asbestos 
fibre  previously  described. 


528 


VOLUMETRIC  ANALYSIS. 


§  99. 


b.  The  known  quantity  of  hydrogen  added  +  \  its  vol.  of  O. 

c.  The  CH4  present  +  2  vols.  of  O  requisite  for  its  combustion. 

CH4  +  O4  =  (CO2  +  2H20) 

V*— ^— ^  V^v^  ^  r          ii»ii  ii      ^ 

2          4          disappears. 

Since  a  and  b  are  known,  or  can  be  readily  calculated  from  the  previous  data, 
by  subtracting  (a+b)  from  the  total  contraction  it  is  possible  to  obtain  C — 
(a+5)  =  c  contraction  due  to  CH4  alone,  and  one-third  of  this  is  equal  to  the 
volume  of  CH4  present,  as  will  be  readily  seen  from  the  above  equation. 
The  remaining  nitrogen  is  estimated  by  difference. 

Improved  arrangement  of  Hempel's  Pipettes  for  storing-  and 
using-  absorbents. — Professor  P.  P.  Beds  on  has  designed  an 
arrangement  of  pipettes  which  he  uses  in  connection  with  a 
Dittmar's  measuring  apparatus,  but  which  may  of  course  be 
used  with  other  forms  of  gas  apparatus  by  suitable  connections. 
The  pipettes  are  shown  in  fig.  94,  and  their  use  may  be  described 
as  follows  : — A  capillary  tube  with  a  three-way  cock  A  is  soldered 

to  the  Hemp  el  pipette — the- 
capillary  is  drawn  out  and  bent 
so  as  to  pass  into  the  mercury 
trough.  The  tap  A  can  be- 
placed  in  connection  with  C,  to- 
which  is  attached  a  movable 
mercury  reservoir  D.  In  work- 
ing, e.g.,  transferring  gas  to  E, 
the  absorbent  fills  E  and  the 
capillary  of  tap  A.  By  raising 
D  the  vessel  C  and  capillary  B 
are  entirely  filled  with  mercury. 
B,  of  course,  is  immersed  in 
the  mercury  trough.  Having^ 
filled  B  with  mercury,  the  test 
tube  containing  the  gas  to  be 
examined  is  brought  over  the 
end  of  B  and  some  gas  drawn 
into  C  by  depressing  D.  The 
tap  is  then  turned  to  put  the 

Fig.  94.  tube  in  connection  with  E,  and 

the    gas    forced    into    E    by 

depressing  the  tube  in  trough.  By  raising  and  lowering  the  tube 
the  gas  can  be  brought  into  intimate  contact  with  the  absorbent 
and  absorption  thus  promoted.  To  bring  all  the  gas  into  E,  D  is 
again  used  and  the  remainder  of  gas  drawn  into  C  by  depressing  D ; 
then  by  turning  the  tap  round  the  gas  from  C  can  be  forced 
into  E;  the  tap  is  then  turned  so  as  to  put  the  capillary  and 
E  in  connection,  and  the  gas  flows  into  E  with  a  small  portion 
in  capillary  B,  retained  by  the  column  of  mercury  filling  the 
bent  limb. 


§    100.  THE   NITROMETEK.  529 

The  gas  may  be  left  thus  for  some  hours ;  and  to  transfer  it  to 
the  tube,  C  and  E  are  placed  in  connection  by  suitably  turning  the 
tap ;  then  by  depressing  D  some  gas  is  drawn  into  C  and  the  tap 
turned  so  as  to  put  C  and  the  tube  in  connection. 

By  carefully  raising  I)  the  mercury  is  washed  out  of  B  and  some 
of  the  gas  passes  into  the  tube.  "With  B  clear  of  mercury  and 
filled  with  gas,  the  tube  and  E  are  placed  in  connection  and  the 
gas  flows  out  of  E  into  the  tube.  When  the  liquid  from  E  has 
risen  so  as  to  fill  the  vessel  up  to  the  tap  (the  capillary  of  the  tap 
being  also  filled),  the  tap  is  turned  to  put  C  and  B  in  connection ; 
then  by  raising  I)  all  gas  is  washed  out  of  C  and  capillary  into  the 
tube  used  for  its  collection  and  transferred  to  the  measuring  tube. 

Professor  Beds  on  also  attaches  to  the  measuring  apparatus  a 
vessel  containing  a  known  volume  of  air  at  known  temperature  and 
pressure,  as  recommended  by  Lunge,  so  as  to  dispense  with  the 
otherwise  necessary  corrections. 

THE    NITROMETER. 

§  100.  THIS  instrument  has  been  incidentally  alluded  to  in  §  67 
(page  247)  as  being  useful  for  the  estimation  of  nitric  acid  in  the 
form  of  nitric  oxide.  It  was  indeed  for  this  purpose  that  the 
instrument  was  originally  contrived,  more  especially  for  ascertaining 
the  proportion  of  nitrogen  acids  in  vitriol. 

The  instrument  has  been  found  extremely  useful  also  for  general 
technical  gas  analysis,  and  for  the  rapid  testing  of  such  substances 
as  manganese  peroxide,  hydrogen  peroxide,  bleaching  powder,  urea, 
etc.  The  apparatus  in  its  simplest  form  is  shown  in  fig.  95,  and 
consists  of  a  graduated  measuring  tube  fitted  at  the  top  with  a 
three-way  stop-cock,  and  a  glass  cup  or  funnel ;  the  graduation 
extends  from  the  tap  downwards  to  50  c.c.  usually,  and  is  divided 
into  TTF  c.c.  The  plain  tube,  known  as  the  pressure  or  level  tube, 
is  about  the  same  size  as  the  burette,  and  is  connected  with  the 
latter  by  means  of  stout  elastic  tubing  bound  securely  with  wire. 
Both  tubes  are  held  in  clamps  on  a  stand,  and  it  is  advisable  to  fix 
the  burette  itself  into  a  strong  spring  clamp,  so  that  it  may  be 
removed  and  replaced  quickly. 

One  great  advantage  over  many  other  kinds  of  technical  gas 
apparatus  which  pertains  to  this  instrument  is,  that  it  is  adapted 
for  the  use  of  mercury,  thus  insuring  more  accurate  measurements, 
and  enabling  gases  soluble  in  water,  etc.,  to  be  examined. 

Another  form  of  the  same  instrument  is  designed  by  Lunge 
for  the  estimation  of  the  nitric  acid  in  saltpetre  and  nitrate  of 
soda,  where  a  larger  volume  of  nitric  oxide  is  dealt  with  than 
occurs  in  many  other  cases.  In  this  instrument  a  bulb  is  blown 
on  the  burette  just  below  the  tap,  and  the  volume  contents  of  this 
bulb  being  found,  the  graduation  showing  its  contents  begins  on  the 
tube  at  the  point  where  the  bulb  ends,  and  thence  to  the  bottom ; 
the  level  tube  also  has  a  bulb  at  bottom  to  contain  the  mercury 

M  M 


530 


VOLUMETRIC  ANALYSIS. 


100. 


displaced  from  the  burette.     Illustrations  of  this  form  of  nitrometer 
will  be  found  further  on. 

The  following  description  of  the 
manipulation  required  for  the  estima- 
tion of  nitrogen  acids  in  vitriol  applies 
to  the  ordinary  nitrometer,  and  applies 
equally  to  the  estimation  of  nitrates 
in  water  residues  and  the  like  (see 
page  248)  :— 

The  burette  a  is  filled  with  mercury  in 
such  quantity  that,  on  raising  b  and  keeping 
the  tap  open  to  the  burette,  the  mercury 
stands  quite  in  the  taphole,  and  about  two 
inches  up  the  tube  b.  The  tap  is  now  closed 
completely,  and  from  0'5  to  5  c.c.  of  the 
nitrous  vitriol  (according  to  strength)  poured 
into  the  cup.  b  is  then  lowered  and  the  tap 
cautiously  opened  to  the  burette,  and  shut 
quickly  when  all  the  acid  except  a  mere 
drop  has  run  in,  carefully  avoiding  the 
passage  of  any  air.  3  c.c.  of  strong  pure 
H2SO4  are  then  placed  in  the  cup  and  drawn 
in  as  before,  then  a  further  2  or  3  c.c.  of 
acid  to  rinse  all  traces  of  the  sample  out  of 
the  cup.  a  is  then  taken  out  of  its  clamp, 
and  the  evolution  of  gas  started  by  inclining 
it  several  times  almost  to  a  horizontal  position 
and  suddenly  righting  it  again,  so  that  the 
mercury  and  acid  are  well  mixed  and  shaken 
for  a  minute  or  two,  until  no  further  gas  is 
evolved.  The  tubes  are  so  placed  that  the 
mercury  in  b  is  as  much  higher  than  that  in 
a  as  is  required  to  balance  the  acid  in  a; 
this  takes  about  one  measure  of  mercury  for 
6' 5  measures  of  acid.  When  the  gas  has 
assumed  the  temperature  of  the  room,  and 
all  froth  subsided,  the  volume  is  read  off, 
and  also  the  temperature  and  pressure  from 
a  thermometer  and  barometer  near  the  place 
of  operation.  The  level  should  be  checked 
by  opening  the  tap,  when  the  mercury  level 
ought  not  to  change.  If  it  rises,  too  much 
pressure  has  been  given,  and  the  reading 
must  be  increased  a  trifle.  If  it  sinks,  the 
reverse.  A  good  plan  is  to  put  a  little  acid 
into  the  cup  before  opening  the  tap :  this 
will  be  drawn  in  if  pressure  is  too  low,  or 
blown  up  if  too  high.  These  indications  will  serve  for  a  correct  repetition 
of  the  experiment. 

To  empty  the  apparatus  ready  for  another  trial,  lower  a  and  open  the  tap, 
then  raise  b  so  as  to  force  both  gas  and  acid  into  the  cup ;  by  opening  the  tap 
then  outwards,  the  bulk  of  the  acid  can  be  collected  in  a  beaker,  the  last 
drops  being  wiped  out  with  blotting-paper.  It  is  hardly  necessary  to  say  that 
the  tap  must  be  thoroughly  tight,  and  kept  so  by  the  use  of  a  little  vaseline, 
taking  care  that  none  gets  into  the  bore-hole. 

The  calculations  for  nitrogen  are  given  on  page  248. 


Fig.  95. 


§  100. 


THE   NITROMETER. 


531 


It  is  evident  that  the  nitrometer  can  be  made  to  replace  Hemp  el's 
burette  if  so  required,  by  attaching  to  the  side  opening  of  the  ^  three- 
way  tap  the  various  pipettes  previously  described,  or  smaller  pipettes 
of  the  same  kind  to  be  used  with  mercury,  as  described  by  Lunge 
(Berichte,  xiv.  14,  92). 

The  instrument  may  also  be  very  well  employed  for  collecting, 
measuring,  and  analyzing  the  gases  dissolved  in  water  or  other 
liquids.  An  illustration  of  this  method  is  given  by  Lunge  and 
Schmidt  (Z.  a.  C.  xxv.  309)  in  the  examination  of  a  sample  of 
water  from  the  hot  spring  at  Leuk  in  Switzerland. 


\ 


\J 


Pig.  96. 


Pig.  97. 


The  determination  of  the  dissolved  gases  was  made  in  the  nitro- 
meter, arranged  as  shown  in  figs.  96  and  97  : — 

The  flask  A  is  completely  filled  with  the  water ;  an  indiarubber  plug  with 
a  capillary  tube  (a)  passing  through  it  is  then  inserted  in  the  flask,  and  the 
tube  is  thereby  completely  filled  with  water.  The  whole  is  then  weighed, 
and  the  difference  between  this  and  the  weight  of  the  empty  flask  and  tube 
gives  the  amount  of  water  taken.  The  end  of  the  capillary  tube  is  then 
connected  to  the  side  tube  of  the  nitrometer  by  the  tube  b.  The  nitrometer 
is  then  completely  filled  with  mercury,  and  when  the  tubes  are  quiet,  the  flask 
and  measuring  tube  of  the  nitrometer  are  quickly  placed  in  connection,  with- 
out the  introduction  of  the  slightest  trace  of  air.  The  water  in  the  flask  is 
then  slowly  heated  to  boiling.  Some  water  as  well  as  the  dissolved  gases 
collect  in  the  measuring  tube  of  the  nitrometer.  The  tube  N  of  the  nitro- 
meter should  be  lowered  in  order  that  the  boiling  may  take  place  under 
reduced  pressure.  .After  boiling  for  five  to  ten  minutes,  the  stop-cock  is 

M   M    2 


532 


VOLUMETRIC   ANALYSIS. 


§  100. 


quickly  turned  through  180°,  so  that  the  flask  is  placed  in  combination  with 
the  cup  B  containing  mercury,  and  the  flame  removed.  Since  the  mercury 
stands  lower  in  N  than  in  M,  it  is  not  possible  for  any  loss  of  gas  to  take 
place  at  the  moment  of  turning  the  tap.  It  is  also  impossible  for  any  gas  or 
steam  to  escape  through  the  mercury  cup,  since  the  pressure  is  inward.  A 
small  bubble  of  gas  always  remains  under  the  stopper ;  this  is  brought  into  M 


50 


Fig.  98. 


Fig.  100. 


by  lowering  the  tube  N  as  much  as  possible,  and  then  turning  the  stop-cock 
so  that  the  flask  and  measuring  tube  are  again  placed  in  connection,  and  when 
the  bubble  has  passed  over,  quickly  reversing  the  tap  again. 

When  the  whole  of  the  gas  is  collected  in  the  nitrometer,  it  is  connected 
with  a  second  instrument  O  P,  quite  full  of  mercury.     The  gas  is  then 


§  100.  LUNGE'S  IMPROVED  NITROMETER.  533 

transferred  by  placing  the  tap  in  such  a  position  that  it  is  closed  in  all 
directions,  and  the  tube  M  is  heated  by  passing  steam  through  the  tube  R. 
When  it  is  quite  hot  the  tube  N  is  lowered,  causing  the  water  in  M  to  boil, 
in  order  to  expel  every  trace  of  dissolved  gas.  The  taps  are  then  placed  in 
connection  and  the  gas  passes  over.  It  can  then  be  cooled,  measured,  and 
submitted  to  analysis,  Two  experiments  gave  505  gm.  water  taken,  gas 
evolved  5'06  c.c.,  =  10'02  per  1000  gm. ;  502  gm.  water  taken,  gas  evolved 
4'94  c.c.,=9'84  per  1000  gm. 

Lunge's  Improved  Nitrometer  for  the  Gas- Volumetric  Analyses 
of  Permanganate,  Chloride  of  Lime,  Manganese  Peroxide,  etc.— 
Professor  Lunge  in  describing  this  instrument  (J.  C.  S.  I.  ix.  21) 

says : — 

"  In  a  paper  published  in  the  ChemiscJie  Industrie,  1885,  161, 1  described 
the  manifold  uses  to  which  the  nitrometer  can  be  put  as  an  apparatus  for 
gas  analysis  proper,  as  an  absorptiometer,  and  especially  for  gas-volumetric 
analyses.  To  fit  it  for  the  last-mentioned  object,  I  added  to  it  a  flask, 
provided  with  an  inner  tube  fused  on  to  its  bottom,  and  suspended  from 
the  side  tube  of  the  nitrometer,  as  shown  in  fig.  98,  which  at  the  same 
time  exhibits  the  Greiner  and  Friedrich's  patent  tap.  This  shows 
how  any  ordinary  nitrometer,  such  as  are  now  found  in  most  chemical 
laboratories,  can  be  applied  to  the  before-mentioned  uses.  "Where,  however, 
the  methods  concerned  are  to  be  employed  not  merely  occasionally,  but 
regularly,  it  will  be  preferable  to  get  a  nitrometer  specially  adapted  to  this 
use,  of  which  figs.  99  and  100  show  various  forms.  They  have  no  cup  at  the 
top,  which  is  quite  unnecessary  for  this  purpose,  but  merely  a  short  outlet 
tube  for  air.  Fig.  99  shows  an  instrument  provided  with  one  of  the  new 
patent  taps,  which  are  certainly  very  handy,  and  cause  a  much  smaller 
number  of  spoiled  tests  than  the  ordinary  three-way  tap,  as  shown  in  fig.  100, 
which  at  the  same  time  exhibits  the  form  of  nitrometer  intended  for  large 
quantities  of  gas,  the  upper  part  being  widened  into  a  bulb,  below  which  the 
graduation  begins  with  either  60  or  100  c.c.,  ending  at  100  or  140  c.c. 
respectively.  There  are  also  various  shapes  of  flasks  shown  in  these 
instruments,  but  it  is  unnecessary  to  say  that  these,  as  well  as  the  bulb 
arrangements,  can  be  applied  to  any  other  form  of  the  instrument.  The 
nitrometers  used  for  gas-volumetric  analyses  are  best  graduated  in  such 
manner  that  the  zero  point  is  about  a  centimeter  below  the  tap,  whilst 
ordinary  nitrometers  have  their  zero  point  at  the  tap  itself.  I  will  say  at 
once  that  for  all  estimations  of  oxygen  in  permanganate,  bleach  or  manganese 
(see  pages  108, 153),*  it  is  quite  unnecessary  to  employ  mercury  for  filling  the 
instruments,  since  identical  results  are  obtained  with  ordinary  tap  water; 
but  it  is  decidedly  advisable  to  place  this  instrument,  like  any  ordinary 
nitrometer  or  any  other  apparatus  in  which  gases  are  to  be  measured,  in 
a  room  where  there  are  as  few  changes  of  temperature  by  cold  draughts  or 
gas-burners  and  so  forth  as  possible. 

"It  may  be  as  well  to  give  here  a  general  description  of  the  mode  of 
procedure  for  manipulating  gas-volumetric  analysis  with  the  nitrometer, 
common  to  all  analyses  according  to  this  method.  Fill  the  nitrometer  with 
water  or  mercury  by  raising  the  level  tube  till  the  level  of  the  liquid  in  the 
graduated  tube  is  at  zero  (in  the  case  of  instruments  bearing  the  zero-mark 
a  little  below  the  tap,  as  in  figs.  99  and  100),  or  at  TO  c.c.  (in  the  case  of 
ordinary  nitrometers,  beginning  their  graduation  at  the  tap  itself).  It  is 
unnecessary  to  say  that  in  the  latter  case  all  readings  must  be  diminished  by 
1  c.c.  Close  the  glass  tap.  Put  the  substance  to  be  tested  into  the  outer 
.space  of  the  flask,  together  with  any  other  reagent  apart  from  the  H2O2  (in  the 

*  An  error  occurs  there  in  describing  the  apparatus  as  the  new  gasvolumeter,  whereas 
it  should  have  been  the  improved  nitrometer. 


534  VOLUMETRIC  ANALYSIS.  §    100. 

case  of  bleaching-powder  nothing  but  the  bleach  liquor,  in  that  of  perman- 
ganate the  30  c.c.  of  sulphuric  acid,  etc.).  Now  put  the  H2O2  into  the  inner 
tube  of  the  flask,  after  having,  in  the  case  of  testing  for  chlorine,  made  it 
alkaline  in  the  previously  described  way.  Put  the  india-rubber  cork,  still 
hanging  from  the  tap,  on  to  the  flask,  without  warming  the  latter  as  above 
described.  As  this  produces  a  compression  of  the  air  within  the  flask, 
remove  this  by  taking  out  the  key  of  the  tap  in  figs.  98  or  99,  or,  in  fig.  100, 
turning  it  for  a  moment  so  as  to  communicate  with  the  short  outlet  tube. 
Now  turn  the  tap  back,  mix  the  liquids  by  inclining  the  flask,  shake  up  and 
allow  the  action  to  proceed.  As  the  gas  passes  over  into  the  graduated  tube, 
lower  the  level  tube,  so  as  to  produce  no  undue  pressure ;  at  last  bring  the 
liquid  in  both  tubes  to  an  exact  level  and  read  off. 

"  In  the  case  of  bleach  analysis  all  the  oxygen  of  the  chloride  of  lime  is 
given  off,  together  with  exactly  as  much  oxygen  of  the  H2O2.  The  total  is 
just  equal  to  the  volume  of  chlorine  gas  which  would  be  given  off  by  the 
chloride  of  lime,  and  thus  immediately  represents  the  French  or  Gay-Lussac 
chlorometric  degrees,  of  course  after  reducing  the  volume  to  0°  and  760  mm. 
pressure.  (The  reading  of  the  barometer  must  be  corrected  by  deducting 
the  tension  of  aqueous  vapour  for  the  temperature  observed  as  well  as  the 
expansion  of  mercury,  according  to  the  tables  found  everywhere).  These 
reductions  can  be  easily  performed  by  the  tables  contained  in  the  "  Alkali- 
Makers'  Pocket-book"  (pages  28  to  39),  which  I  had  calculated  a  number  of 
years  ago,  just  in  order  to  facilitate  the  use  of  the  nitrometer." 

Lunge's  O-asvolumeter  is  an  apparatus  for  dispensing  with 
reduction  calculations  in  measuring  gas  volumes  (described  by 
Professor  Lunge  in  Zeitslirift  f.  anc/eic.  Cliem.  1890,  139 — 144, 
and  here  quoted  from  /.  S.  0.  I.  ix.  547). 

In  technical  gas  analysis  a  considerable  amount  of  time  is  taken 
up  by  calculations  for  reducing  gas  volumes  to  standard  temperature 
and  pressure.  In  pure  gas  analysis  the  inconvenience  is  not  so 
great ;  for  technical  purposes  the  initial  and  end  temperature  and 
pressure  may  be  taken  as  the  same,  owing  to  the  short  duration  of 
the  experiment,  and  for  more  accurate  purposes  "compensators" 
have  been  devised.  Where,  however,  the  gas  to  be  measured  is 
evolved  from  a  weighed  quantity  of  a  liquid  or  solid  (so  that; 
volume  and  weight  have  finally  to  be  connected)  the  matter  is 
different,  and  readings  of  thermometer  and  barometer  have  to  be 
made,  and  then  the  necessary  calculations  are  to  be  gone  through. 
Tables  of  reduction  have  certainly  been  compiled  for  reduction  of 
gases  at  various  temperatures  and  pressures,  but  still  readings  of 
thermometer  and  barometer  have  to  be  made,  and  part  of  the  time 
only  is  sa*ved.  To  further  reduce  the  time  occupied  and  to  render 
*the  technical  chemist  in  this  department  to  a  great  extent 
independent  of  temperature  and  atmospheric  pressure  the  present 
apparatus  has  been  constructed. 

By  means  of  a  f-tube,  D  (fig.  101),  and  thick-walled  rubber  tubing, 
are.  connected  vthe  three  tubes  A,  B,  C.  A  is  for  measuring  the  gas;  it 
may  be  any  form  of  nitrometer,  a  Bunte's  burette  or  other,  convenient 
burette.  B  is  the  "  reduction  tube,"  which  has  at  its  upper  end  a  spherical 
or  cylindrical  bulb.  The  volume  to  the  first  mark  is  100  c.c.,  the  remaining 
narrow  portion  of  the  tube  being  calibrated  up  to  130 — 140  c.c.  in  divisions 
representing  1TV  c.c.  This  "reduction  tube"  is  set  once  for  all  at  the 


§  100, 


LUNGE'S  GASVOLUMETER. 


535 


beginning  of  work  by  observing  thermometer  and  barometer,  calculating  the 
volume  which  100  c.c.  of  perfectly  dry  air,  measured  at  0°  C.  and  760  m.m., 
would  occupy  under  the  existing  conditions.  This  quantity  of  air  is  then 
introduced,  and  the  tube  closed  by  means  of  the  stop-cock  shown,  or  by 
fusing  up  the  inlet  (having  in  place  of  the  inlet  tube  shown  in  the  figure 
a  tube  of  capillary  bore).  If  it  be  necessary  to  measure  the  gas  moist  a  drop 
of  water  is  introduced  into  this  tube,  and  of  course  in  the  calculation 
necessary  the  barometric  pressure  must  be  reduced  by  the  vapour  tension  of 
water ;  if  the  gases  are  to  be  measured  perfectly  dry  (as,  for  instance,  when 
using  the  nitrometer  with  sulphuric  acid),  a  drop  of  sulphuric  acid  takes  the 
place  of  the  water. 

C  is  the  pressure  or  levelling  tube. 

If  necessary  for  the  purpose  of 
regulating  the  temperature  A  and  B 
may  be  surrounded  with  water-jackets. 
A,  B,  and  C  are  supported  by  spring 
clamps.  It  is  easily  seen  that  when  by 
raising  C  the  level  of  the  mercury  in 
B  has  been  forced  up  to  the  mark 
100,  exactly  the  amount  of  pressure  is 
exerted  by  C  as  will  compress  the  gas 
in  B  to  its  volume  under  standard 
conditions. 

In  taking  a  reading  A  and  B  must  be 
levelled  and  the  mercury  level  in  B  must 
have  been  brought  up  to  100.  The 
volume  shown  on  A  is  then  the  volume 
reduced  to  standard  temperature  and 
pressure.  In  cases  where  the  gas  is 
generated  in  A  itself,  or  where  the  gas 
is  transferred  to  A,  this  is  all  that 
need  be  done.  If,  however,  the  gas  is 
generated  in  a  side  apparatus,  as  shown 
in  fig.  101,  A  and  C  must  first  be 
levelled  and  the  stop-cock  of  A  then' 
closed  so  that  the  gas  in  A  is  collected 
at  atmospheric  pressure.  After  this 
reduction  may  be  effected  as  already 
explained. 

In  nitrogen  determinations  by 
Dumas'  method,  A  contains  caustic 
potash  as  well  as  mercury;  this  is 
compensated  by  having  on  the  reduc- 
tion tube,  B,  a  mark  at  a  distance 
below  the  100  mark  equal  to  one-tenth 
of  the  height  of  the  caustic  potash 
column  (sp.  gr.  of  the  caustic  potash 
equals  one-tenth  sp.  gr.  of  mercury) ; 
when  taking  a  reading  the  mercury  in 
B  must  be  at  100,  and  that  in  A  must 
be  on  a  level  with  this  new  lower  mark 
of  B.  Similar  allowance  may  be  made 
in  nitrometric  determinations,  but  the 
case  is  here  more  difficult,  owing  to 
the  variations"  in  the  quality  and  specific 
gravity  of  the  sulphuric  acid  used.  It 


Fig.  101. 


is  better  in  such  cases  to  liberate  the  gas  in  a  separate  vessel  and  transfer 
subsequently  to  the  burette  for  reduction  and  measurement.  Fig.  101 
shows  a  convenient  form  of  apparatus.  Of  course  the  working  part  E,  i1 


536 


VOLUMETRIC  ANALYSIS. 


§    100. 


need  not  be  graduated.  Before  beginning  the  operation  the  mercury  is 
made  to  fill  E  with  the  side  tube  a,  which  side  tube  is  then  capped  with 
a  caoutchouc  stopper  to  prevent  escape  of  the  mercury  during  subsequent 
shaking.  A,  with  its  side  tube  e,  is  also  completely  filled  with  mercury. 
The  substance  under  examination,  and  subsequently  the  acid,  are  added 
through  C  as  usual.  To  transfer  the  gas  from  E  to  A,  the  cap  b  is  removed 
and  a  is  fitted  to  e  by  means  of  the  rubber  connection  d.  F  is  then  raised 
and  C  lowered,  the  taps  are  carefully  opened,  and  transference  effected  until 
the  acid  in  E  just  fills  e. 


Fig.  102. 

A  further  saving  of  time  may  be  effected  in  works,  where  the 
instrument  is  to  be  used  for  always  one  and  the  same  object,  by 
marking  on  the  gas  burette  or  nitrometer  the  weight  in  milligrams 
corresponding  to  certain  volumes ;  this  may  be  done  either  instead 


§  100. 


LUNGE'S  GAS  VOLUMETER. 


537 


of  or  alongside  the  c.c.  divisions ;  or  by  using  a  fixed  quantity  of 
substance,  percentages  may  be  marked  off  directly.  For  nitrogen 
determinations  by  Dumas'  method  1  c.c.  of  nitrogen  under  normal 
conditions  weighs  1*254  m.gm.  In  the  case  of  azotometric  deter- 
minations of  ammoniacal  nitrogen  (by  sodic  hypobromite)  the 
graduations  may  be  made  to  represent  ammonia.  Correction  must 
be  made  in  graduating,  however,  for  the  incompleteness  of  the 
reaction.  Tables  giving  the  corrections  have  been  introduced,  but 
the  author  has  shown  (Cliem.  Ind.  1885,  165)  that  these  may  be 
dispensed  with,  and  that  it  is  sufficient  to  make  a  correction  of  2*5 
per  cent.  For  urea,  however,  the  correction  is  9  per  cent. 

The   following   table   shows    substances   for   which   gasometric 
methods  are  used : — 


Substance. 

Basis  to  which 
Percentages  are 
Calculated. 

Method 
Employed. 

Gas 
Evolved. 

1  c.c.  of  Gas 
=m.gm.  of  Basis, 
(Col.  II.) 

Organic  substances 
Ammonia  salts   .  .  . 

Urine  

Nitrogen 

Ammonia 
Urea 

Dumas' 
Hypobrmte. 

N 
N 
N 

N 

1-254 
1-285* 
1-561* 

2"952* 

Bone-charcoal,  etc. 

55                          55 

Pyrolusite  

Carbon  dioxide 

Calcic  carbonate 
Manganese  dioxide 

Decomposed 
with  HC1 

By  H2O2 

CO2 
CO2 

o 

1-966 

4-468 
3'882 

Bleaching  powder 
Potassic    perman- 
ganate ... 

Chlorine 
Oxygen 

5> 
59 

o 

o 

1-5835 
0-715 

Chili  saltpetre    ... 
Nitrous  bodies    ... 

55                        )»' 
55                          55 

55                          39 

Nitroglycerol,  dy- 
namite, etc  

Nitrocellulose,  py- 
roxylin      

Sodic  nitrate 
N203 
HNO3 
Nitric  acid  36°  B. 
Sodic  nitrate 

Trinitroglycerol 
Nitrogen 

55 

Nitrometer 

35 

35 
33 
53 

NO 
NO 
NO 
NO 
NO 

NO 
NO 
NO 

3-805 
1-701 
2-820 
5-330 
3-805 

3-387 
0-6267 
0-6267 

*  The  corrections  above  referred  to  have  here  already  been  made. 


HUBERT  DYER. 


538 


VOLUMETRIC  ANALYSIS. 


§    100. 


TABLE  for  Correction  of  Volumes  of  Gases  for  Temperature, 
according  to  the  Formula  V1^ 

1  +  5  t  from  0°  to  30°.     8  -  0'003665. 


t 

1-f  5t 

Log.  (1  +  S  1) 

t 

1  +  St 

Log.  (1  +  5*) 

t 

l  +  5t 

Log.  (1  +  S  t) 

6-0 

i-ooooooo 

o-ooo  oooo 

5-0 

1-0183250 

0-007  8864 

16-0 

1-0366500 

0-015  6321 

•i 

1-0003665 

1591 

•1 

1-0186915 

0-008  0427 

•1 

1-0370165 

7857 

•2 

1-0007330 

3182 

•2 

1-0190580 

1989 

•9 

2 

T0373830 

9391 

•3 

1-0010995 

4772 

•3 

1-0194245 

4551 

.r 

1-0377495 

0-016  0925 

•4 

1-0014660 

6362 

•4 

1-0197910 

5112 

'4 

1-0381160 

2459 

0-5 

1-0018325 

7951 

5'5 

1-0201575 

6672 

10-5 

1-0384825 

3992 

•6 

1-0021990 

9540 

•6 

1-0205240 

8232 

•6 

1-0388490 

5524 

•7 

1-0025655 

0-001  1128 

•7 

1-0208905 

9791 

4l 

"•4 

1-0392155 

7056 

•8 

1-0029320 

2715 

•8 

1-0212570 

0'009  1350 

•8 

1-0395820 

8588 

•9 

1-0032985 

4302 

5-9 

1-0216235 

2909 

10-9 

1-0399485 

0-017  0118 

1-0 

1-0036650 

0-001  5888 

6-0 

1-0219900 

0-009  4466 

ll'O 

1-0403150 

0-017  1648 

•1 

1-0040315 

7473 

•1 

1-0223565 

6024 

•1 

1-0406815 

3178 

•2 

1-0043980 

9058 

'2 

1-0227230 

7580 

•2 

1-0410480 

4708 

•3 

1-0047645 

0-002  0643 

•3 

1-0230895 

9136 

•^ 

1-0414145 

6236 

•4 

1-0051310 

2227 

•4 

1-0234560 

0-010  0692 

•4 

1-0417810 

7764 

T5 

1-0054975 

3810 

6-5 

1-0238225 

2247 

11-5 

1-0421475 

9292 

•6 

1-0058640 

5393 

•6 

1-0241890 

3801 

•6 

1-0425140 

0-018  0819 

•7 

1-0062305 

6974 

•7 

1-0245555 

5355 

*7 

T0428805 

2346 

•8 

1-0065970 

8556 

•8 

1-0249220 

6908 

•8 

1-0432470 

3871 

1-9 

1-0069635 

0-003  0137 

6-9 

1-0252885 

8461 

11-9 

1-0436135 

5397 

2-0 

1-0073300 

0-003  1718 

7*0 

L-0256550 

0-011  0013 

12'0 

1-0439800 

0-018  6922 

•1 

1-0076965 

3298 

•1 

1-0260215 

1565 

•1 

1-0443465 

8446 

•2 

1-0080630 

4877 

•2 

1-0263880 

3116 

"2 

1-0447130 

9970 

•3 

1-0084295 

6455 

•3 

1-0267545 

4666 

'3 

1-0450795 

0-019  1493 

•4 

1-0087960 

8033 

•4 

1-0271210 

6216 

•4 

1-0454460 

3016 

2'5 

1-0091625 

9611 

7'5 

1-0274875 

7765 

12-5 

1-0458125 

4538 

•6 

1-0095290 

0-004  1188 

•6 

1-0278540 

9314 

•6 

1-0461790 

6060 

•7 

1-0098955 

2764 

•7 

1-0282205 

0-012  0863 

•7 

1-0465455 

7581 

•8 

1-0102620 

4340 

•8 

1-0285870 

2410 

•8 

1-0469120 

9102 

2-9 

1-0106285 

5916 

7-9 

1-0289535 

3957 

12-9 

1-0472785 

0-020  0622 

3-0 

1-0109950 

0-004  7490 

8-0 

1-0293200 

0-012  5504 

13-0 

1-0476450 

0-020  2141 

•1 

1-0113615 

9064 

•1 

1-0296865 

7050 

•1 

1-0480115 

3660 

•2 

1-0117280 

0-005  0638 

•2 

1-0300530 

8596 

•2 

1-0483780 

5179 

•3 

1-0120945 

2211 

•3 

1-0304195 

0-013  0141 

•3 

1-0487445 

6697 

•4 

1-0124610 

3783 

•4 

1-0307860 

1685 

•4 

1-0491110 

8214 

3'5 

1-0128275 

5355 

8-5 

1-0311525 

3229 

13-5 

1-0494775 

9731 

•6 

1-0131940 

6926 

•6 

1-0315190 

4772 

•6 

1-0498440 

0'021  1248 

•7 

1-0135605 

8497 

•7 

1-0318855 

6315 

•7 

1-0502105 

2764 

•8 

1-0139270 

0-006  0067 

•8 

1-0322520 

7857 

•8 

1-0505770 

4279 

3-9 

1-0142935 

1636 

8-9 

1-0326185 

9399 

13-9 

1-0509435 

5794 

4-0 

1-0146600 

0-006  3205 

9-0 

1-0329850 

0-014  0940 

14-0 

1-0513100 

0-021  7308 

•1 

1-0150265 

4774 

•1 

1-0333515 

2481 

•1 

1-0516765 

8822 

•2 

1-0153930 

6342 

•2 

1-0337180 

4021 

•2 

1-0520430 

0-022  0335 

•3 

1-0157595 

7909 

•3 

1-0340845 

5560 

•3 

1-0524095 

1848 

•4 

1-0161260 

9476 

•4 

1-0344510 

7099 

•4 

1-0527760 

3360 

4'5 

1-0164925 

0-007  1042 

9'5 

1-0348175 

8638 

14-5 

1-0531425 

4873 

•6 

1-0168590 

2607 

•6 

1-0351840 

0-015  0175 

•6 

1-0535090 

6382 

•7 

1-0172255 

417? 

•7 

1-0355505 

1713 

•7 

1-0538755 

7893 

•8 

1-0175920 

5737 

•8 

1-0359170 

3250 

•8 

1-0542420 

9403 

4-9 

1-0179585 

7301 

9-9 

1-0362835 

4786 

14-9 

1-0546085 

0-023  0193 

§    100;  TABLES.  539 

TABLE  for  Correction  of  Volumes  of  Gases— continued. 


t 

1+  5t 

Log.  (1  +  5  t) 

t 

l+5t 

Log.  (1  +  5  1) 

t 

l+5t 

Log.  (1  +  5  1) 

15-0 

1-0549750 

0-023  2422 

20-0 

1-0730000 

0-030  7211 

25-0 

1-0916250 

0-038  0734 

•1 

1-0553415 

3930 

•1 

1-0736665 

8694 

•1 

1-0919915 

2192 

•2 

1-0557080 

5438 

•2 

1-0740330 

0-031  0176 

•2 

1-0923580 

3650 

•3 

1-0560745 

6946 

•3 

1-0743995 

1658 

•  Q 
«J 

1-0927245 

5107 

•4 

1-0564410 

8452 

•4 

1-0747660 

3139 

•4 

1-0930910 

6563 

15-51-0568075 

9959 

20-5 

1-0751325 

4620 

25-5 

1-0934575 

8020 

•6  1-0571740 

0-024  1465 

•6 

1-0754990 

6100 

•6 

1-0938240 

9474 

•71-0575405 

2970 

•7 

1-0758655 

7580 

"7 

1-0941905 

0-039  0929 

•8:1-0579070 

4475 

•8 

1-0762320 

9059 

•8 

1-0945570 

2384 

15-91-0582735 

5979 

20-9 

1-0765985 

0-032  0538 

•9 

1-0949235 

3838 

1 

16-0  1-0586400 

0-024  7483 

21-0 

1-0769650 

0-032  2016 

26-0 

1-0952900 

0-039  5291 

-ljl-0590065 

8986 

•1 

1-0773315 

3493 

•1 

1-0956565 

6745 

•2 

1-0593730 

0'025  0489 

•2 

1-0776980 

4971 

'2 

1-0960230 

8197 

•3 

1-0597395 

1991 

•3 

1-0780645 

6447 

"3 

1-0963895 

9649 

•4 

1-0601060 

3493 

•4 

1-0784310 

7924 

'4 

1-0967560 

0-040  1101 

16'5 

1-0604725 

4994 

21-5 

1-0787975 

9399 

26-5 

1-0971225 

2551 

•6 

1-0608390 

6495 

•6 

1-0791640 

0-033  0874 

•6 

T0974890 

4002 

•7 

1-0612055 

7995 

•7 

1-0795305 

2349 

'  i 

1-0978555 

5452 

•8 

1-0615720 

9495 

•8 

1-0798970 

3823 

•8 

1-0982220 

6901 

16-9 

1-0619385 

0-026  0994 

21-9 

1-0802635 

5298 

•c 

1-0985885 

8351 

17'0 

1-0623050 

0-026  2492 

22-0 

1-0806300 

0-033  6771 

27-0 

1-0989550 

0'04a  9800 

•1 

1-0626715 

3990 

•1 

1-0809965 

8243 

•1 

1-0993215 

0-041  1247 

•2 

1-0630380 

5488 

'2 

1-0813630 

9715 

.<• 

1-0996880 

2695 

•3 

1-0634045 

6985 

•3 

1-0817295 

0-034  1186 

.c 

1-1000545 

4143 

•4 

1-0637710 

8482 

•4 

1-0820960 

2658 

'4 

1-1004210 

5589 

17-5 

1-0641375 

9978 

22-5 

1-0824625 

4129 

27-5 

1-1007875 

7036 

•6 

1-0645040 

0-027  1473 

•6 

1-0828290 

5598 

•6 

1-1011540 

8481 

•7 

1-0648705 

2968 

'7 

1-0831955 

7069 

"7 

1-1015205 

9926 

•8 

1-0652370 

4462 

•8 

1-0835620 

8538 

•8 

1-1018870 

0*042  1371 

17-9 

1-0656035 

5956 

22-9 

1-0839285 

0-035  0006 

•c 

1-1022535 

2815 

18'0 

1-0659700 

0-027  7450 

23-0 

1-0842950 

0-035  1475 

28-0 

1-1026200 

0-042  4259 

•1 

1-0663365 

8943 

•1 

1-0846615 

2942 

•] 

1-1029865 

5703 

•2 

1-0667030 

0-028  0435 

•2 

1-0850280 

4409 

.«• 

1-1033530 

7145 

•3 

1-0670695 

1927 

.0 

C 

1-0853945 

5876 

-J 

1-1037195 

8587 

•4 

1-0674360 

3418 

*4 

1-0857610 

7342 

1-1040860 

0-043  0029 

18.5 

1-0678025 

4909 

23-5 

1-0861275 

8808 

28-5 

1-1044525 

1471 

•6 

1.0681690 

6400 

•6 

1-0864940 

0-036  0273 

•6 

1-1048190 

2911 

•7 

1-0685355 

7889 

'7 

1-0868605 

1738 

'7 

1-1051855 

4352 

•8 

1-0689020 

9379 

•8 

1-0872270 

3202 

•8 

1-1055520 

5792 

18-91-0692685 

0-029  0868 

23-9 

1-0875935 

4666 

•c 

1-1059185 

7231 

19-01-0696350 

0-029  2356 

24-0 

1-0879600 

0-036  6129 

29-0 

1-1062850 

0-043  8671 

•11-0700015 

3844 

•1 

1-0883265 

7592 

•] 

1-1066515 

0-044  0109 

•2 

1-0703680 

5331 

•c 

1-0886930 

9054 

.( 

1*1070180 

1546 

•3 

1-0707345 

6818 

•3 

1-0890595 

0-037  0517 

"t 

1-1073845 

2985 

•4 

1-0711010 

8304 

'4 

1-0894260 

1978 

1-1077510 

4422 

19'5 

1-0714675 

9790 

24-5 

1-0897925 

3438 

29'5 

1-1081175 

5858 

•6 

1-0718340 

0-030  1275 

•6 

1-0901590 

4899 

'6 

1-1084840 

7295 

•7 

1-0722005 

2760 

,H 

1-0905255 

6359 

.t 

1-1088505 

8730 

•8 

1-0725670 

4244 

•8 

1-0908920 

7817 

•8 

1-1092170 

0-045  0165 

19-9 

1-0729335 

5728 

•( 

1-0912585 

9277 

•{ 

1-1095835 

1600 

30-0 

1-1099500 

0-045  3035 

540 


VOLUMETRIC   ANALYSIS. 


§  100. 


TABLE  for  Correction  of  Volumes  of  Gases  for 
Temperature,  giving  the   Divisor   for   the   Formula 


V  x 


'760  x  (1  +  S«). 


t 

760  x 
(l  +  5t). 

Log.  [760  x 
(l  +  5t)]. 

t 

760  x 
(1  +  St). 

Log.  [760  x 
(1  +«*)]. 

t 

760  x 
(l+5t). 

Log.  [760  x 
(l+8t)]. 

o-o 

760-0000 

2-880  8136 

4-0 

771-1416 

2-887  1341 

8-0 

782-2832 

2-893  3640 

•1 

760-2785 

9727 

•1 

771-4201 

2910 

•1 

782-5617 

5186 

•2 

760-5571 

2-881  1319 

•2 

771-6987 

4478 

•2 

782-8403 

6732 

•3 

760-8356 

2908 

•3 

771-9772 

6044 

•3 

783-1188 

8276 

•4 

761-1142 

4498 

•4 

772-2558 

7611 

•4 

783-3974 

9821 

0'5 

761-3927 

6087 

4-5 

772-5343 

9178 

8-5 

783-6759 

2-894  1365 

•6 

761-6712 

7676 

•6 

772-8128 

2-888  0743 

•6 

783-9544 

2908 

•7 

761-9498 

9264 

•7 

773-0914 

2309 

•7 

784-2330 

4452 

•8 

762-2283 

2-882  0851 

•8 

773-3699 

3872 

•8 

784-5115 

5994 

•9 

762-5069 

2437 

•9 

773-6485 

5437 

•9 

784-7901 

7536 

i-o 

762-7854 

2-882  4024 

5-0 

773-9270 

2-888  7000 

9-0 

785-0686 

2-894  9076 

•1 

763-0639 

5610 

•1 

774-2055 

8563 

•1 

785-3471 

2-895  0617 

•2 

763-3425 

7194 

•2 

774-4841 

2-8890125 

MB 

it 

785-6257 

2157 

•3 

763-6210 

8779 

•3 

774-7626 

1686 

*2 

785-9042 

3696 

•4 

763-8996 

2-883  0362 

•4 

775-0412 

3248 

•4 

786-1828 

5235 

T5 

764-1781 

1947 

5-5 

775-3197 

4808 

9-5 

786-4613 

6774 

•6 

764-4566 

3528 

•6 

775-5982 

6368 

•6 

786-7398 

8311 

•7 

764-7352 

5111 

•7 

775-8768 

7927 

•7 

787-0184 

9849 

•8 

765-0137 

6692 

•8 

776-1553 

9487 

•8 

787-2969 

2-896  1385 

"9 

765-2923 

8273 

•c 

776-4339 

2-890  1044 

•9 

787-5755 

2923 

2-0 

765-5708 

2-883  9854 

6-0 

776-7124 

2-890  2602 

10-0 

787-8540 

2-896  4457 

•1 

765-8493 

2-884  1433 

•1 

776-9909 

4159 

•1 

788-1325 

5993 

•2 

766-1279 

3013 

•2 

777*2695 

5716 

•  o 

2 

788-4111 

7528 

•3 

766-4064 

4591 

•fl 
c 

777-5480 

7272 

.0 

788-6896 

9061 

•4 

766-6850 

6170 

'4 

777-8266 

8828 

•4 

788-9682 

2-8970595 

2-5 

766-9635 

7747 

6-5 

778-1051 

2-891  0383 

10-5 

789-2467 

2128 

•6 

767-2420 

9323 

•6 

778-3836 

1937 

•6 

789-5252 

3660 

•7 

767-5206 

2-885  0900 

•7 

778-6622 

3491 

*7 

789-8038 

5192 

•8 

767-7991 

2476 

•8 

778-9407 

5044 

•8 

790-0823 

6724 

•9 

768-0777 

4052 

•c 

779-2193 

6597 

•c 

790-3609 

8255 

3-0 

768*3562 

2-885  5626 

7-0 

779-4978 

2-891  8149 

ll'O 

790-6394 

2-897  9785 

•1 

768-6347 

7200 

•l 

779-7763 

9701 

•1 

790-9179 

2-898  1315 

•2 

768-9133 

8772 

*c 

780-0549 

2-892  1251 

.£• 

791-1965 

2844 

•3 

769-1918 

2-886  0347 

•J 

780-3334 

2802 

.r 

791-4750 

4373 

•4 

769-4704 

1919 

'4 

780*6120 

4352 

'^ 

791-7536 

5901 

3-5 

769-7489 

3491 

7-5 

780-8905 

5901 

11-5 

792-0321 

7428 

•6 

770-0274 

5061 

•6 

781-1690 

7450 

•6 

792-3106 

8954 

•^7 

770-3060 

6633 

*7 

781-4476 

8998 

"7 

792-5892 

2-899  0482 

•8 

770-5845 

8203 

•8 

781-7261 

2-893  0547 

•8 

792-8677 

2008 

•c 

770-8631 

9773 

.c 

782-0047 

2094 

•9793-1463 

3534 

1 

§    100.  TABLES.  541 

TABLE  for  Correction  of  Volumes  of  Gases— continued. 


t 

760  x 
(1+St). 

Log.  [760  x 
(1  +  8t)J. 

t 

760  X 
d+5t). 

Log.  [760  x 
(1  +  »*)]. 

t 

760  x 

a+8y. 

Log.  [760  x 
(1  +  St)]. 

12-0 
•1 
•2 
•3 

•4 

793-4248 
793-7033 
793-9819 
794-2604 
794-5390 

2-899  5057 
6583 
8106 
9629 
2-900  1153 

16-5 
•6 

•7 
•8 
•9 

805-9591 
806-2376 
806-5162 
806-7947 
807-0733 

2-906  3131 
4630 
6131 
7631 
9130 

21-0 
•1 
•2 
•3 
•4 

818-4934 
818-7719 
819-0505 
819-3290 
819-6076 

2'913  0152 
1629 
3107 
4584 
6059 

12-5 

•6 
•7 
•8 
•9 

794-8175 
795-0960 
795-3746 
795-6531 
795-9317 

2674 
4196 
5717 
7238 
8758 

17-0 
•1 
•2 
•3 
•4 

807-3518 
807*6303 
807-9089 
808-1874 
808-4660 

2-907  0627 
2126 
3624 
5121 
6617 

21-5 
•6 

•7 
•8 
21-9 

819*8861 
820-1646 
820-4432 
820-7217 
821-0003 

7535 
9010 
2-914  0485 
1959 
3434 

13-0 
•1 
•2 
•3 

•4 

796-2102 
796-4887 
796-7673 
797-0458 
797-3244 

2-901  0277 
1796 
3316 
4833 
6351 

17-5 
•6 

•7 
•8 
•9 

808-7445 
809-0230 
809*3016 
809-5801 
809-8587 

8114 
9609 
2-908  1103 
2599 
4092 

22-0 
•1 
•2 
•3 

•4 

821-2788 
821-5573 
821-8359 
822-1144 
822-3930 

2-914  4906 
6379 
7852 
9322 
2-915  0794 

13'5 

•6 
•7 
•8 
•9 

797-6029 
797-8814 
798-1600 
798-4385 
798-7171 

7867 
9383 
2-902  0900 
2415 
3931 

18-0 
•1 
•2 
•3 

•4 

810-1372 
810-4157 
810-6943 
810*9728 
811-2514 

2-908  5586 
7079 
8572 
2-909  0063 
1554 

22-5 
•6 

"7 
•8 
•9 

822-6715 
822-9500 
823-2286 
823-5071 
823-7857 

2265 
3734 
5204 
6674 
8143 

14-0 
•1 
•2 
"3 
•4 

798-9956 
799-2741 
799-5527 
799-8312 
800-1098 

2-902  5444 
6958 
8471 
9983 
2-903  1496 

18'5 
•6 

•7 
•8 
"9 

811-5299 
811-8084 
812-0870 
812-3655 
812-6441 

3046 
4535 
6026 
7515 
9004 

23-0 
•1 
•2 
•3 
•4 

824-0642 
824-3427 
824-6213 
824-8998 
825-1784 

2-915  9610 
2-916  1078 
2546 
4012 
5478 

14-5 
•6 
*7 
•8 
•9 

800-3883 
800-6668 
800-9454 
801-2239 
801-5025 

3008 
4518 
6029 
7539 
9049 

19-0 
•1 
•2 

•4 

812-9226 
813-2011 
813-4797 
813-7582 
814-0368 

2-910  0492 
1980 
3468 
4953 

6440 

23-5 
•6 

•7 
•8 
•9 

825-4569 
825-7354 
826-0140 
826-2925 
826-5711 

6944 
8409 
9874 
2-917  1339 
2802 

15-0 
•1 
•2 

•q 

•4 

801-7810 
802-0595 
802-3381 
802-6166 
802-8952 

2-904  0557 
2067 
3574 
5081 
6589 

19-5 
•6 

•7 
•8 
•c 

814-3153 
814-5938 
814-8724 
815-1500 
815-4295 

7927 
9411 
2-911  0896 
2380 
3865 

24-0 
•1 
•2 
•3 
•4 

826-8496 
827-1281 
827-4067 
827-6852 
827-9638 

2-917  4265 
5728 
7191 
8652 
2-918  0114 

15-5 

•6 
•7 
•8 
•c 

803-1737 
803-4522 
803-7308 
804-0093 
804-2879 

8095 
9601 
2-905  1106 
2612 
4116 

20-0 
•1 
*2 

"3 
•4 

815-7080 
815-9865 
816-2651 
816-5436 
816-8222 

2-911  5347 
6830 
8313 
9794 
2-912  1276 

24*5 
•6 

•7 
•8 
24-9 

828-2423 
828-5208 
828-7994 
829-0779 
829-3565 

1574 
3034 
4495 
5953 
7413 

16-0 
•1 
•2 

•  € 

€ 

•4 

804-5664 
804-8449 
805-1235 
8-5-4020 
805-6806 

2-905  5618 
7122 
8625 
2-906  0127 
1629 

20-5 
•6 

"7 
•8 
•c 

817'1007 
817-3792 

817-6578 
817-9363 
818-2149 

2756 
4236 
5716 
7195 

8674 

25-0 
•1 
'2 

•4 

829-6350 
829-9135 
830-1921 
830-4706 
830-7492 

2-918  8871 
2-919  0329 
1786 
3242 
4699 

542  VOLUMETRIC   ANALYSIS.  §    100. 

TABLE  for  Correction  of  Volumes  of  Gases— continued. 


t 

760  x 

a  +  &>. 

Log.  [760  x 
(1  +  5*)]. 

t 

760  x 

(1-T-St) 

Log.  [760  x 
(1  +  «t]. 

t 

760  x 
(1+St). 

! 
Log.  [760  x 
(1  +  5t)]. 

25-5831-0277 
•6831-3062 
•7831-5848 
•8831-8633 
25-9832-1419 

2-9196155 
7610 
9065 
2-920  0520 
1974 

27-0 
•1 
•2 
•3 
•4 

835-20582-9217935 
835-4843;           9384 
835-7629  2-922  0831 
836-0414J           2279 
836-3200           3725 

28-5839-3839 
•6839-6624 
'7839-9410 
•8840-2195 
28-9840-4981 

2-923  9607 
2-924  1047 
2488 
3928 
5368 

] 

832-4204 
832-6989 
832-9775 
833-2560 
833-5346 

2-920  3427 
4880 
6333 
7784 
9236 

27-5 
•6 

•7 
•8 
27-9 

836-5985 
836-8770 
837-1556 
837-4341 
837-7127 

5172 
6616 
8062 
9507 
2-923  0951 

29-0  840*7766  2-924  6806 
•1841-0551           8245 
•2841-3337           9683 
•3841-61222-9251120 
•4841-8908           2558 

26-5 
26-9 

833-8131 
834-0916 
834-3702 
834-6487 
834-9273 

2-921  0688 
2137 
3588 
5038 
6487 

28-0 
•1 
'2 
•3 
*4 

837-9912 
838-2697 
838-5483 
838-8268 
839-1054 

2-923  2394 
3838 
5281 
6723 
8165 

29-5842-1693 
•6842-4478 
'7,842-7264 
•8843-0049 
29-9843-2835 

3995 
5431 
6866 
8301 
9737 

30-0 

843-5620|2-926  1170 

§  100. 


TABLES. 


543 


Pressure  of  Aqueous  Vapour  in  Millimeters  of  Mercury, 
from  -  9' 9°  to  +  35°  C. 


m.m. 

m.m. 

m.m. 

m.m. 

m.m. 

m.m. 

-9-9 

2-096 

-5-4 

3-034 

-6-9 

4-299 

3-5 

5-889 

8'0 

8-017 

12-5 

10-804 

•8 

•114 

•3 

•058 

•8 

•331 

•6 

•930 

•1 

•072 

•6 

•875 

7 

•132 

•2 

•082 

•7 

•364 

•7 

•972 

•2 

•126 

,tj 

4 

•947 

•6 

•150 

•1 

•106 

•6 

•397 

•8 

6-014 

•3 

•181 

'     -8 

11-019 

'0 

•168 

-5-0 

•131 

'5 

•430 

3-9 

•055 

•4 

•236 

12-9 

•090 

-9-4 

•186 

-4-9 

3-156 

-0-4 

•463 

4-0 

6-097 

8-5 

•291 

13-0 

11-162 

•3 

•204 

•8 

•181 

•3 

•497 

•1 

•140 

•6 

•347 

•1 

•235 

•2 

•223 

•7 

•206 

•2 

•531 

•2 

•183 

7 

•404 

"£ 

•309 

•1 

•242 

•6 

•231 

•1 

•565 

•3 

•226 

•8 

•461 

'c 

•383 

-9-0 

•261 

•5 

•257 

-o-o 

4-600 

•4 

•270 

8-9 

•517 

•4 

•456 

-8-9 

2-280 

-4'4 

•283 

+  o-o 

4-600 

4.5 

•313 

9-0 

8-574 

13-5 

•530 

•8 

•299 

•3 

•309 

•1 

•633 

•6 

•357 

•1 

•632 

•6 

•605 

7 

•318 

•2 

•335 

•2 

•667 

•* 
/ 

•401 

•2 

•690 

7 

•681 

•6 

•337 

•1 

•361 

•3 

•700 

•8 

•445 

•3 

748 

•8 

757 

•5 

•356 

-4-0 

•387 

•4 

•733 

4-9 

•490 

•4 

•807 

13-9 

•832 

-8-4 

•376 

-3-9 

3-414 

0-5 

•767 

5-0 

6-534 

9-5 

•865 

14-0 

11-908 

•3 

•396 

•8 

•441 

•6 

•801 

•1 

•580 

•6 

•925 

•1 

•986 

•2 

•416 

"7 

•468 

•7 

•836 

•  O 

Z 

•625 

7 

•985 

.<• 

12-064 

•1 

•436 

•6 

•495 

•8 

•871 

•  ^ 
t 

•671 

•8 

9*045 

1 

•142 

-8-0 

•456 

'5 

•522 

0-9 

•905 

•4 

717 

9-9 

•105 

•4 

•220 

-7'9 

2-477 

-3-4 

•550 

1-0 

4-940 

5-5 

763 

10-0 

9'165 

14-5 

•298 

•8 

•498 

•3 

•578 

•1 

•975 

•6 

•810 

•1 

•227 

•6 

•378 

7 

•519 

•2 

•606 

•2 

5*011 

•7 

•857 

•2 

•288 

"/ 

•458 

•6 

•540 

•1 

•634 

•3 

•047 

•8 

•904 

•3 

•350 

•8 

•538 

•5 

•561 

-3'0 

•662 

•4 

•082 

5-9 

•951 

•4 

•412 

14-9 

•619 

-7'4 

•582 

-2-9 

3-691 

T5 

•118 

6-0 

6-998 

10-5 

•474 

15-0 

12-699 

•3 

•603 

•8 

•720 

•6 

•155 

•1 

7-047 

•6 

•537 

•1 

•781 

•2 

•624 

"7 

•749 

•7 

•191 

•2 

•095 

7 

•601 

•9 

j| 

•864 

•1 

•645 

•6 

•778 

•8 

•228 

•3 

•144 

•8 

•665 

•3 

•947 

-7-0 

•666 

'5 

•807 

1-9 

•265 

•4 

•193 

10-9 

728 

'4 

13-029 

-6'9 

2-688 

-2-4 

•836 

2-0 

5-302 

6-5 

•242 

11-0 

9-792 

15-5 

•112 

•8 

•710 

•3 

•865 

•] 

•340 

•6 

•292 

•1 

•857 

•6 

•197 

•7 

•732 

•2 

•895 

•2 

•378 

•7 

•342 

•2 

•923 

7 

•281 

•6 

•754 

•1 

•925 

•3 

•416 

•8 

•392 

•3 

•989 

•8 

•366 

•5 

•776 

-2-0 

•955 

•4 

•454 

6-9 

•442 

•4 

10-054 

15-9 

•451 

-6-4 

•798 

-1-9 

3-985 

2-5 

•491 

7-0 

7-492 

11-5 

•120 

16-0 

13-536 

•3 

•821 

•8 

4-016 

•6 

•530 

•1 

•544 

•6 

•187 

•1 

•623 

•2 

•844 

"7 

•047 

•7 

•569 

•2 

•595 

7 

•255 

•2 

710 

•1 

•867 

•6 

•078 

•8 

•608 

•3 

•647 

•8 

•322 

•3 

797 

-6-0 

•890 

'5 

•109 

2.9 

•647 

•4 

•699 

11-9 

•389 

•4 

•885 

-5'9 

2-914 

-1-4 

•140 

3-0 

5-687 

7-5 

•751 

12-0 

10-457 

16-5 

•972 

'8 

•938 

•3 

•171 

•1 

•727 

•6 

•804 

•1 

•526 

•6 

14-062 

•7 

•962 

•2 

•203 

•2 

•767 

•7 

•857 

•2 

•596 

7 

•151 

•6 

•986 

•1 

•235 

•3 

•807 

•8 

•910 

•3 

•665 

•8 

•241 

•5 

3-010 

i-o 

•267 

•4 

•848 

7-9 

•964 

•4 

734 

16-9 

•331 

544  VOLUMETRIC  ANALYSIS. 

Pressure  of  Aqueous  Vapour — continued. 


§  ioo. 


in.m. 

in.ru. 

m.m. 

m.m. 

m.m. 

m.m. 

17-0 

14-421 

20-0 

17*391 

2°3'0 

20*888 

26-0 

24-988 

29*0 

29-782 

32-0 

35-359 

•1 

•513 

•1 

•500 

•1 

21-016 

•1 

25-138 

•1 

•956 

•1 

•559 

•2 

•605 

»C 

2 

•608 

*2 

•144 

•2 

•288 

•2 

30-131 

•2 

•760 

•3 

•697 

•  C 

tJ 

•717 

•3 

•272 

•3 

•438 

•3 

•305 

•3 

•962 

'4 

•790 

'4 

•826 

'4 

•400 

•4 

•588 

•4 

•479 

•4 

36-165 

17-5 

•882 

20-5 

•935 

23-5 

•528 

26-5 

'738 

29-5 

•654 

32-5 

•370 

•6 

•977 

•6 

18-047 

•6 

•659 

•6 

•891 

•6 

•833 

•6 

•576 

•7 

15-072 

•7 

•159 

•7 

•790 

•7 

26-045 

•7 

31-011 

•7 

•783 

•8 

•167 

•8 

•271 

•8 

•921 

•8 

•198 

•8 

•190 

•8 

•991 

17-9 

•262 

20-9 

•383 

23-9 

22-053 

26-9 

•351 

29-9 

•369 

32-9 

37-200 

18-0 

15-357 

21-0 

18-495 

24-0 

22-184 

27-0 

26-505 

30-0 

31-548 

33-0 

37-410 

•1 

•454 

•1 

•610 

•1 

•319 

•1 

•663 

•1 

•729 

•1 

•621 

•2 

•552 

"2 

•724 

•2 

•453 

•2 

•820 

•2 

•911 

•2 

•832 

•3 

•650 

•3 

•839 

•3 

•588 

•3 

•978 

•3 

32-094 

•3 

38-045 

•4 

•747 

•4 

•954 

•4 

•723 

•4 

27-136 

•4 

•278 

•4 

•258 

18-5 

•845 

21-5 

19-069 

24-5 

•858 

27-5 

•294 

30'5 

•463 

33-5 

•473 

•6 

•945 

•6 

•187 

•6 

•996 

•6 

•455 

•6 

•650 

•6 

•689 

•7 

16-045 

•7 

•305 

•7 

23-135 

•7 

•617 

•7 

•837 

"7 

•906 

•8 

•145 

•8 

•423 

•8 

•273 

•8 

•778 

•8 

33-026 

•8 

39-124 

18-9 

•246 

21'9 

•541 

24-9 

•411 

27'9 

•939 

30-9 

•215 

33-9 

•344 

19-0 

16-346 

22-0 

19-659 

25-0 

23-550 

28-0 

28-101 

31-0 

33-405 

34-0 

39-565 

•1 

•449 

•1 

•780 

•1 

•692 

•1 

•267 

•1 

•596 

•1 

•786 

•2 

•552 

•2 

•901 

•2 

•834 

•2 

•433 

•2 

•787 

•2 

40-007 

•3 

•655 

•3 

20-022 

•3 

•976 

•3 

•599 

•3 

•980 

•3 

•230 

•4 

•758 

•4 

•143 

•4 

24-119 

•4 

•765 

•4 

34-174 

•4 

•455 

19'5 

•861 

22-5 

•265 

25-5 

•261 

28-5 

•931 

31-5 

•368 

34-5 

•680 

•6 

•967 

•6 

•389 

•6 

•406 

•6 

29-101 

•6 

•564 

•6 

•907 

•7 

17-073 

•7 

•514 

•7 

•552 

•7 

•271 

•7 

•761 

•7 

41-135 

•8 

•179 

•8 

•639 

•8 

•697 

•8 

•441 

•8 

•959 

•8 

•364 

19'9 

•285 

22-9 

•763 

25-9 

•842 

28-9 

•612 

31-9 

35-159 

34-9 

•595 

35-0 

•827 

INDEX. 


Absorption  apparatus,  Mohr's,  118 
Absorption  apparatus,  Fresenius',117 
Absorption  equivalents  shown  by  oils 

and  fats  for  bromine,  342 
Acetates,  alkaline  and  earthy,  titration 

of,  83 

Acetate  of  lime,  analysis  of,  83 
Acetates,  metallic,  83 
Acidimetry,  80 
Acidimetry,  delicate  end-reaction  for, 

81 

Acid,  acetic,  titration  of,  82 
Acid,  arsenic,  titration  of,  87 
Acid,  carbolic,  titration  of,  348 
Acid,  carbonic,  estimation  of,  91 
Acid,  chromic,  titration  of  iron  -with, 

111 

Acid,  citric,  titration  of,  85 
Acid  liquors,  tartaric,  90 
Acid,  nitric,  pure  for  titrations,  128 
Acid,  oxalic,  titration  of,  86 
Acid,  phosphoric,  titration  of,  86,  2G9 
Acid,  tannic,  titration  of,  316 
Acid,  tartaric,  titration  of,  88 
Acid,  uric,  estimation  of,  368 
Acids,  combined  in  neutral  salts,  101 
Acids,  mineral,  in  vinegar,  82 
Acids,  titration  of,  80 
Acids,  titration  of  by  iodine  and  thio- 

sulphate,  81 
Aerated  distilled  water,  preparation  of, 

259 

Air  and  carbonic  anhydride  gas,  analy- 
sis of,  469 

Air,  carbonic  acid  in,  titration  of,  95 
Air,  estimation  of  oxygen  in,  469 
Air,  examination  of,  by  Hal  dan  e  and 

Pembrey's  method,  96 
Air,  examination  of  by  A  n  g  u  s  S  m  i  t  h '  s 

minimetric  method,  96 
Air,  expired,  examination  of,  95 
Albumen  in  urine,  estimation  of,  372 
Albuminoid  ammonia  process,  442 
Alkalies,  caustic  and  carbonated,  titra- 
tion of,  51—53 
Alkalies  caustic,  titration  of,  by  potas- 

sic  bichromate,  55 
Alkalies,  indirect  estimation  of,  125 
Alkalies    in    presence    of     sulphites, 

titration  of,  54 
Alkaliraeter,  Schuster's,  6 
Alkalimetric  estimation  of  various  me- 
tallic salts,  101 


Alkalimetric    methods,   extension    of, 

102 

Alkalimetry,  30 

Alkalimetry,  Gay  Lussac's,  30 
Alkaline  carbonates,  titration  of,  50 
Alkaline  compounds,  commercial,  59 
Alkaline  earths,  indirect  estimation  of, 

125 

Alkaline  earths,  titration  of,  65 
Alkaline    earths,   titration    of    mixed 

hydrates  and  carbonates,  65 
Alkaline  tartrate  solution,  for  sugar 

estimation,  295 

Alkaline  permanganate,  for  water  ana- 
lysis, 437 

Alkaline  salts,  titration  of,  50 
Alkaline  silicates,  titratiou  of,  63 
Alkaline  sulphides,  titration  of,  59,  60 
Alloys  of  silver,  assay  of,  285 
Alumina,  estimation  of,  204 
Alumina  in  caustic  soda,  etc.,  estima- 
tion of,  205 
Aluminic  sulphates,  estimation  of  free 

acid  in,  205 

Ammonia,  albumenoid  process,  442 
Ammonia,  combined,  estimation  of,  68 
Ammonia,  estimation  of,  68 
Ammonia,  indirect  titration  of,  70 
Ammonia  in  urine,  estimation  of,  370 
Ammonia  in  water,  estimation  of,  382 
Ammonia,  semi-normal,  44 
Ammonia,    sulphate    of,     estimation, 

71,  75 

Ammonia,  technical  estimation  of,  71 
Ammoniacal  liquor,  table  showing  the 
amount    of    sulphate    obtainable 
from,  75 
Ammonic   molybdate,   standard,   282, 

351 

Ammonio-cupric  solution,  normal,  45 
Analyses,  saturation,  30 
Analysis  by  oxidation  or  reduction,  105 
Analysis  by  precipitation,  123 
Analysis,  factors  for  calculation,  26 
Analysis,  gas,  simple  methods  of,  470 
Analysis  of  substances  by  distillation 

with  hydrochloric  acid,  117 
Analysis,  volumetric  and  gravimetric, 

distinction  between,  2 
Analysis,  volumetric  and  gravimetric^ 
fundamental  distinction  between,  2 
Analysis,    volumetric,    general    prin- 
ciples, 1 

N    N 


546 


INDEX. 


Analysis,  volumetric,  methods  of  classi- 
fication, 3 

Analysis,  volumetric,  systematic,  23, 
24 

Analysis,  volumetric,  without  burettes,  6 

Analysis,  volumetric,  without  weights,  5 

Analysis,  water,  reagents  for,  374 

Antimony,  estimation  of,  as  sulphide, 
136 

Antimony,  estimation  of,  by  bichro- 
mate, 135 

Antimony,  estimation  of,  by  iodine, 
334 

Antimony,  estimation  of,  by  perman- 
ganate, 135 

Antimony  in  presence  of  tin,  estimation 
of,  134 

Antimony,  titration  of,  by  stannous 
chloride,  165 

Apparatus,    absorption,   Fresenius', 

Apparatus,  absorption,  Mohr's,  118 

Apparatus,  Bischof's,  for  evapora- 
tion, 386 

Apparatus  for  iodine  distillation, 
Stortenbeker's,  180 

Apparatus  for  chlorine  distillation,  117, 
118,  180 

Apparatus  for  CO2,  Scheibler's,  98 

Apparat  us  for  gas  analysis  ( B  u  n  s  e  n '  s 
method),  452-465 

Argol,  titration  of.  90 

Arseniates,  estimation  of,  by  iodine, 

Arseniates,  estimation  of,  by  silver,  139 
Arseniates,  estimation  of,  by  uranium, 

138 

Arsenic  acid,  titration  of,  87,  137 
Arsenic,  estimation  of,  by  bichromate, 

138 
Arsenic,  estimation  of,  by  distillation, 

Arsenic,  estimation  of,  by  iodine,  136 
Arsenic,  estimation  of,  by  silver,  139 
Arsenic,  estimation  of,  by  uranium,  138 
Arsenical  ores,  analysis  of,  139 
Arsenic  us  acid  and  iodine  analyses,  121 
Asbestos,  palladium,  476 
Ash,  black,  titration  of,  60 
Aspirator  for  gases,  471 

Backward  titration,  29,  50 

Balance,  the,  5 

Baric  chloride,  preparation  of  normal, 

Barium  in  neutral  salts,  66 

Barium,  estimation  of,  as  chromate,  141 

Barium,  titration  of,  by  permanganate, 

Baryta  solution  for  removing  phos- 
phates and  sulphates  from  urine. 

Baryta  solution,  standard,  44 
Base,  Millon's,  use  of,  44 
Beale's  filter,  18 
Beverages,  carbonic  acid  in,  94 


Bicarbonates  in  presence  of  carbonates, 

titration  of,  53 

Bichromate,  standard  solution  of,  112 
Bischof's  apparatus  for  evaporation, 

386 

Bismuth,  estimation  of,  as  oxalate,  142 
Bismuth,  estimation  of,  as  phosphate, 

143 

Bleaching  compounds,  titration  of,  151 
Bleaching  powder,  gasometric  estima- 
tion of,  152 
Bleaching    powder,    titration    of,    by 

arsenious  solution,  152 
Bleaching    powder,    titration    of,    by 

iodine,  152 
Blue,  Porrier's,  35 
Boric  acid  and  borates,  titration   of, 

334 

Bottle  for  digestion  in  iodine  estima- 
tions, 120 

Bromates,  titration  of,  by  iodine,  154 
Bromine,   absorption   of,  by  oils  and 

fats,  340 
Bromine,  colour  method  of  estimation, 

144 
Bromine,  estimation  of,  by  digestion, 

144 
Bromine,  estimation  of,  by  distillation, 

144,  145 
Bromine,  estimation  of,  by  Cavazzi's 

method,  145 
Bromine,   estimation  of,    by  McCul- 

loch's  method,  145 
Bromine,  indirect  estimation  of,  144 
Bromine,  iodine,  and  chlorine  together, 

181 

Bullets  for  gas  analysis,  how  made,  467 
Burette,  Bin ks',  8,  13 
Burette,  Binks',  or  Gay  Lussac's, 

objections  to,  8 
Burette  clips,  13 
Burette  for  hot  titrations,  11 
Burette,  Gay  Lussac's,  8,  10,  12 
Burette,  Mohr's,  7,  8 
Burette,  Mohr's,  advantages  of,  8 
Burette,  the,  6 
Burette,  the  blowing,  10 
Burette,  the  foot,  10 
Burette,  the  tap,  8,  9 
Burette,  without  pinchcock,  14 
Burette    with    enclosed    thermometer 

float,  figure  of,  8 
Burette,  with  reservoir,  11,  12 
Burette,  with  thermometer  float,  9 
Burette,  with  oblique  tap,  8 
Burettes    and    pipettes,     verification 

of,  22 

Butter,  titration  of,  337 
Butylic    hydride    gas,   estimation    of, 
466 

Cadmium,   estimation   of,  as   oxalate. 

147 
Cadmium,  estimation  of,  as  sulphide, 

Calcium,  estimation  of,  as  oxalate,  147 


INDEX. 


547 


Calcium,   estimation    of,  by    perman- 
ganate, 148 
Calcium,  estimation  of,  in  slags  and 

mixtures,  149 

Calcium  in  neutral  salts,  66 
Calibration  of  gas  apparatus  for  water 

analysis,  395 

Carbolic  acid,  titration  of,  348 
Carbon  disulphide,  titration  of,  349 
Carbon  in  iron  and  steel,  estimation 

of,  200 

Carbon  tetrachloride,  use  of,  for  titra- 
tion of  fats,  341 
Carbonates,   Pettenkofer's    method 

for,  93 

Carbonates  alkaline,  titration  of,  51 — 53 
Carbonates,  analysis  of,  91 
Carbonates,  indirect  estimation  of,  125 
Carbonates  soluble  in  acids,  92 
Carbonates  soluble  in  water,  91 
Carbonates,  titration  of,  in  presence  of 

bicarbonates,  53 

Carbonic  acid  in  air,  titration  of,  95 
Carbonic  acid  in  beverages.  94 
Carbonic  acid  in  waters,  93 
Carbonic  anhydride  gas,  estimation  of, 

in  gas  apparatus,  469 
Carbonic  oxide  gas,  estimation  of,  472 
Cathetometer,  the,  16 
Caustic  alkalies,  titration  of,  by  potassic 

bichromate,  55 

Caustic  and  carbonated  alkalies,  titra- 
tion of,  50—57 

Caustic  soda  or  potash,  titration  of,  50 
Centimeter,  cubic,  the,  18 
Cerium,  estimation  of,  149 
Chlorates,  indirect  estimation  of,  125 
Chlorates,  titration  of,  by  iodine,  154 
Chloride  of  lime,  titration  of,  152 
Chlorine  and  silver  analyses,  123 
Chlorine,  bromine,  and  iodine  together, 

estimation  of,  181 

Chlorine,  direct  precipitation  with  sil- 
ver, 150 
Chlorine,  estimation  of,  by  distillation, 

151 

Chlorine  estimations,  indirect,  125 
Chlorine,  estimation  of,  by  silver  and 

chromate  indicator,  150 
Chlorine  gas,  titration  of,  151 
Chlorine,  indirect  estimation    of,    by 

silver  and  sulphocyanogen,  150 
Chlorine  in  waters,  estimation  of,  413, 

439 

Chlorine  water,  titration  of,  151 
Chromate  indicator  for  silver,  124 
Chromates,   estimation  of  by  distilla- 
tion, 155 

Chrome  iron  ore,  analysis  of,  155 
Chromic  acid  in  iron  titration,  111 
Chromium,  titration  by  iron,  154 
Citrates,  titration  of,  85 
Citro-magnesic  solution  for  phosphates, 

271 

Clark's  process  for  softening  water, 
428 


Clips  for  burettes,  7,  13 

Coal  gas,  analysis  of,  508 

Coal  gas,  estimation  of  sulphuretted 

hydrogen  in,  315 

Coal  gas,  estimation  of  sulphur  in,  306 
Cobalt,  estimation  of,  by  permanganate, 

157 

Cobalt,  estimation  of,  as  cyanide,  158 
Cochineal  indicator,  31 
Colorimeter,  directions  for  using,  129 
Colorimeter,  the  Mills',  130 
Colour   reactions,   device    for   seeing, 

124,  128 

Colour  reactions,  precision  in,  128 
Commercial  alkaline  compounds,  59 
Condenser  for  Kjeldahl  method,  78 
Congo  red,  35,  38 
Constants  used  in  the  analysis  of  oils 

and  fats,  344 
Copper  and  iron,  titration  of,  in  same 

liquid,  165 
Copper,  iron,  and  antimony,  estimation 

of,  in  same  liquid,  166 
Copper,  extraction  from  ores,  168 
Copper,  estimation  of,  as  iodide,  161 
Copper,  estimation  of,  as  sulphide,  164 
Copper,     estimation     of,     by     colour 

titration,  171 
Copper,    indirect    estimation    of,    by 

silver,  167 

Copper  ores,  technical  analysis  of,  167 
Copper,  separation  of,  by  electrolysis, 

Copper  in  presence  of  iron,  titration  of, 
163,  172  _ 

Copper  solution  for  sugar,  Fehling's, 
295 

Copper  solution,  Pavy's,  for  sugar, 
303 

Copper,  titration  of,  by  cyanide,  162 

Copper,  titration  of,  by  permanganate, 
160,  161 

Copper,  titration  of,  by  stannous 
chloride,  165 

Correct  reading  of  graduated  instru- 
ments, 16 

Corrections  for  temperature  of  solu- 
tions, 20,  21 

Cubic  centimeter,  the,  18,  19 

Cupric  oxide  for  combustions,  376 

Cuprous  chloride  for  water  analysis, 
377 

Cyanides,  alkaline,  titration  of,  by 
silver,  173,  175 

Cyanogen,  titration  of,  by  iodine,  174 

Cyanogen,  titration  of,  by  mercury, 
174 

Cyanogen,  titration  of,  by  silver,  173 

Decem,  the,  22 
Decimal  system,  origin  of,  18 
Decimillem,  the,  23 
Decinormal  bichromate  solution,  112 
Decinormal  iodine,  preparation  of,  114 
Decinormal  permanganate  solution,  106 
Decinormal  salt  solution,  124 
N   X    2 


548 


INDEX. 


Decinormal  silver  solution,  123 
Decinormal  potassic  arsenite,  121 
Decinormal  sodic  chloride,  124 
Decinormal  sulphocyanate,  127 
Decinormal  thiocyanate,  127 
Dextrine,  inversion  of,  294 
Dextrose,  298 
Digesting  bottle  for  iodine  estimation, 

120 

Direct  and  indirect  processes,  28 
Dissolved  oxygen  in  waters,  446 
Dropping  apparatus  for  silver  assay, 

Earths,  alkaline,  titration  of,  65 

Erdmann's  float,  16 

Estimations,    indirect,    by    means    of 

silver  and  chromate,  125 
Ethyl  gas,  estimation  of,  466 
Ethylic  hydride  gas,  estimation  of,  466 
Eudiometer,  B  u  n  s  e  n '  s ,  calibration  of, 

459 

Explosion  of  gases,  474,  504 
Extension  of  alkalimetric  methods,  102 

Factors  for  calculation  of  analyses,  26 
Fats  and  oils,  titration  equivalents  of, 

with  potash,  336 
Fats  and  oils,  titration  of,  with  bromine 

or  iodine,  336 

Fehling's  copper  solution,  295 
Ferric  compounds,  reduction  of,  189 
Ferric  indicator  for  analyses  by  sulpho- 

cyanogen,  127 
Ferric  iron,  titration  of  by  stannous 

chloride,  190 

Ferric  standard,  to  prepare,  191 
Ferricyanides,  titration  of,  176 
Ferrocyanides  in  alkali  waste,  176 
Ferrocyanides  in  gas  liquor,  176 
Ferrocyanides,  titration  of,  175 
Ferro-Manganese,  estimation  of  man- 
ganese in,  209 
Ferrous  iron,  how  obtained  for  titration, 

189 

Filter,  Beale's,  18 
Filter,  Porter-Clark,  429 
Filter  for   baric    sulphate,   Wilde  n- 

stein's,  313 
Flasks,  measuring,  15 
Float,  Erdmann's,  16 
Float,  with  thermometer,  9 
Fluorescin,  35 
Frankland's      and      Ward's      gas 

apparatus,  493 
Frankland's  joint  for  gas  apparatus, 

394 

Free  acid  in  urine,  estimation  of,  371 
Free  ammonia  in  water,  382,  441 
Fresenius'  absorption  apparatus,  117 
Fruit  juices,  titration  of,  85 

Galactose,  298 

Gas  analysis,  Bunsen's  apparatus  for 

452-489 
Gas  analysis,  calculations  for,  482—489 


Gas  analysis,  normal  solutions  for,  521 
Gas  analysis,  simple  methods  of,  520 
Gas  apparatus,  etching  of,  456 
Gas    apparatus,    Frankland's,     for 

water  analysis,  392 

Gas  apparatus,  Reiser's  portable,  516 
Gas  burette,  Hempel's,  522 
Gas  liquor,  analysis  of,  71 — 75 
Gas  liquor,  spent,  analysis  of,  74 
Gas  liquor,  table  showing  the  amount 
of  sulphate  of  ammonia  to  be  ob 
tained  from,  75 

Gas  pipettes,  Bedson's  modified,  528 
Gas  pipettes,  Hempel's,  524—526 
Gasvolumeter,  Lunge's,  534 
Gases,  analysis  of,  452 
Gases,  explosion  of,  474,  504 
Gases,  indirect  estimation  of,  474 
Gases,  simple  titration  of,  520 
Gases  soluble  in  water,  estimation  ofr 

by  the  nitrometer,  531 
Glucose  or  grape  sugar,  293 
Glycerin,  titration  of,  345 
Glycerin,   estimation   of,   by  perman- 
ganate, 345 

Glycerin,   estimation    of,    by    bichro- 
mate, 346 
Glycerin,  estimation  of,  by  the  acetin. 

method,  347 

Glycerol,  titration  of,  345 
Gold,  estimation  of,  178 
Graduated  instruments,  correct  reading 

of,  16 

Grain  measures,  22 
Grains,  fluid,  22 

Haematites,  analysis  of,  197 

Hardness  of  water  estimated  without 

soap  solution,  66 
Hardness  of  water,  soap  solution  for, 

380 
Hardness  in  waters,  estimation  of,  66, 

413 

Hardness  in  waters,  table  of,  41 5 
Hardness    in    waters,    Frankland's 

table  for,  415 

Hempel's  gas  burette,  512 
Hempel's  gas  pipettes,  524—526 
Hot  titrations,  burette  for,  11 
Hydrobromic  acid  gas,  estimation  of, 

466 
Hydrocarbon  gases,  estimation  of,  466, 

473 

Hydrochloric    acid,    analysis    of    sub- 
stances by  distillation  with,  117 
Hydrochloric  acid,  normal,  43 
Hydrocyanic    acid,    titratioa    of,    by 

silver,  173 

Hydriodic  acid  gas,  estimation  of,  466 
Hydrochloric  acid  gas,  estimation  of, 

466 
Hydrosulphuric   acid    gas,    estimation 

of,  466 
Hydrogen  apparatus,  Bunsen's,  475,. 

476 
Hydrogen  peroxide,  titration  of,  268 


INDEX. 


549 


H 


n  sulphuretted,   titration  of, 


Hypobromite  solution  for  urea,  361 
Hyposulphite  of  soda,  Schiitzenber- 
ger's  solution  of,  258 

Improved  gas  apparatus,  489 
Indicator,    ferric,    for    analyses     by 

sulphocyanogen,  127 
Indicator,  starch,  preparation  of,  116 
Indicator,  chromate,  for  silver,  124 
Indicator    for    mercuric    solutions    in 

sugar  analysis,  296 
Indicators,  30 
Indicators,  azo,  32 
Indicators,  combination  of,  39 
Indicators,  external  and  internal,  29 
Indicators,  various  effects  of  heat  and 

cold  on,  36 
Indicators,  Thompson's  results  with, 

36 
Indicators,  general  characteristics  of, 

37 

Indicators,  table  of  results  with,  39 
Indigo  solution,  standard,  240 
Instruments  graduated,  correct  reading 

of,  16 
Instruments  graduated,  verification  of, 

lodate,  how  to  remove  from  alkaline 

iodides,  114 

lodates,  titration  of,  154 
Iodine,  absorption  of,  by  oils  and  fats, 

340 
Iodine,  estimation  of,  by  distillation, 

179 
Iodine,  estimation  of,  by  Gooch  and 

Browning's  method,  182 
Iodine,  bromine,  and  chlorine,  mixed, 

estimation  of,  181 

Iodine,  estimation  of,  by  chlorine,  183 
Iodine,  estimation  of,  by  nitrous  acid 

and  carbon  bisulphide,  185 
Iodine,  estimation  of,  by  permanganate 

and  thiosulphate,  184 
Iodine  solution,  decinormal,  verification 

of,  115 
Iodine,  titration  of,  by  sulphocyanate 

and  silver,  183 
Iodine,  titration  of,  by  silver  and  starch 

iodide,  186 

Iodine  solution,  decinormal,  prepara- 
tion of,  114 
Iodine  and  thiosulphate,  titrations  by, 

113 
Iodine   and   arsenious   acid    analyses, 

121 

Iodized  starch-paper,  121 
Iron    compounds,    reduction    of,    for 

titration^lll 
Iron,  estimation  of,  with  bichromate, 

186 
Iron,  estimation  of,  by  colour  titration, 

194 

Iron  ore,  magnetic,  analysis  of,  198 
Iron  ore,  spathose,  analysis  of,  198 


Iron  ores,  analysis  of,  195 
Iron  ores,  to  render  soluble,  196 
Iron  in  silicates,  estimation  of,  199 
Iron,    titration   of,    by    thiosulphate, 

192,  193 
Iron,  titration  in  ferrous  state,  186 

Keiser's  gas  apparatus,  516 

Kjeldahl's  method  for  nitrogen,  76 — 
80 

Kjeldahl  method,  substances  in  which 
their  nitrogen  may  be  estimated 
by,  80 

Kjeldahl  method,  modification  of  for 
nitrates,  80 

Kjeldahl  method,  apparatus  and  solu- 
tions for,  77 

Knapp's  standard  mercuric  cyanide, 
296,  368 

Lacmoid  paper,  35 
Lacmoid,  preparation  of,  35 
Lacmoid  solution,  35 
Lead  acetates,  titration  of,  201 
Lead,  as  carbonate,  estimation  of,  203 
Lead,  as  sulphide,  estimation  of,  203 
Lead,  estimated  as  oxalate,  201 
Lead,  estimation  of,  as  chromate,  202 
Lead,  estimation  of  as  molybdate,  351 
Lead,  red,  titration  of,  201 
Lees,  tartaric,  titration  of,  90 
Lemon  juice,  titration  of,  85 
Levulose,  298 

Lime  acetate,  analysis  of,  83 
Lime  and  magnesia  in  urine,  369 
Lime  and  magnesia  in  waters,  66 
Lime,  chloride  of,  gasometric  estima- 
tion, 153 

Lime,  estimation  of  (see  Calcium),  148 
Lime  juice,  titration  of,  85 
Liquid  for.  suspending  precipitates,  132 
Liquors,  red,  examination  of,  60 
Litmus  indicator,  30 
Litmus,  interference  in,    by  carbonic 

acid,  31 

Litmus  paper,  31 
Litmus,  pure  extract  of,  30 
Litmus,  preparation  of,  30 
Litmus,  preservation  of,  30 
Litmus,  use  of,  by  artificial  light,  31 
Logarithms    for    use    in    volumetric 

analysis,  448 
Lunge's  nitrometer,  529 
Lyes,  soda,  examination  of,  60 

Magnesia  and  lime  in  urine,  369 
Magnesia  and  lime  in  waters,  66 
Magnesia,  estimation  of,  204 
Magnesia  mixture,  272 
Magnesia,  titration  of,  87,  204 
Magnesic -citrate    solution    for    phos- 
phates, 271 

Magnesite,  use  of,  for  preventing  re- 
gurgitation  in  distilling  chlorine, 
118 
Magnetic  iron  ore,  analysis  of,  198 


550 


INDEX. 


Magnesium  as  reducing  agent  for  ferric 

salts,  111 

Maltose  or  malt  sugar,  292,  293,  299 
Manganese,  estimation  of,  by  distilla- 
tion with  hydrochloric  acid,  215 
Manganese,  estimation  of,  by  gas  appa- 
ratus, 213 

Manganese,  estimation  of,  by  iron,  217 
Manganese,   estimation  of,   by  oxalic 

acid,  216 
Manganese,estimationby  Pattinson's 

method,  207 
Manganese  in  small  quantities,  estima- . 

tion  of,  212 

Manganese  ores,  analysis  of,  214 
Manganese,  ores  and  alloys  of,  208 
Manganese  ores,  moisture  in,  214 
Manganese  oxides,  nature  of,  206 
Manganese,  precipitation  as  dioxide,  207 
Manganese,  precipitation  of,  by  per- 
manganate, 210 

Manganese,  technical  method  of  esti- 
mating, 211 

Marsh  gas,  estimation  of,  466 
Me  Leod's  gas  apparatus,  495 
Measuring  flasks,  15 
Mercurial  trough,  394 
Mercuric  cyanide,  standard  for  sugar, 

296 

Mercuric  iodide  for  sugar,  296 
Mercury,  estimation,  as  chloride,  219 
Mercury,  estimation  of,  as  iodide,  221 
Mercury,  estimation  of,  by  cyanogen, 

222 

Mercury,  preservation  of,  for  gas  appa- 
ratus, 462 

Mercury  solution  for  urea,  357 
Mercury,  titration  of,  by  iodine,  220 
Mercury,  titration  of,  by  thiosulphate, 

220 
Metallic  salts  of  all  kinds,  alkalimetric 

titration  of,  102 

Metals  and  minerals  in  waters,  estima- 
tion of,  416 

Method  for  percentages,  26 
Method,  minimetric  for  examination  of 

air,  96 

Methyl  gas,  estimation  of,  466 
Methyl  orange,  33 

Methyl  orange,  the  proper  use  of,  33 
Methyl  orange,  commercial,  the  defects 

of,  33 

Millon's  base,  use  of,  44 
Mills'  colorimeter,  130 
Milk  sugar,  inversion  of,  293 
Milk  sugar,  inverted,  300 
Mineral  acids  in  vinegar,  82 
Mirror  for  detecting  precipitates,  313 
Mixer,  test,  17 

Mixtures  of  sugars,  titration  of,  304 
Mohr  Dr.  F.,  father  of  the  volumetric 

system,  23 

Mohr' s  burette,  advantages  of,  8 
Molybdenum,  titration  of,  350 
Molybdenum  solution  for  precipitating 
phosphoric  acid,  272,  436 


Napthol  j8,  for  titrating  bromine,  340 
Nessler's    solution,    preparation    of, 

374,  437 

Nickel,  estimation  of,  223 
Nitrate  baths  for  photography,  assay 

of,  290 
Nitrates,    colorimetric    estimation   of, 

248 
Nitrates,  estimation  of,  by  ferrous  salts, 

228 
Nitrates,  estimation  of,  by  nitrometer, 

247 

Nitrates,  indirect  estimation  of,  125 
Nitrates  in  water,  aluminium  proce?s 

for,  408 
Nitrates  in   water,   estimation  of,  in 

nitrometer,  440 

Nitrates  by  Kjeldahl  method,  80  ^ 
Nitrates,  technical  method  of  titration, 

238 

Nitric  acid,  estimation  of,  by  distilla- 
tion, 225 
Nitric  acid,  estimation  of,  by  indigo, 

239 
Nitric  acid,  estimation  of,  in  absence  of 

organic  matter,  228 
Nitric  acid,  estimation  of,  in  presence 

of  organic  matter,  232-238 
Nitric  acid,  normal,  43 
Nitric  acid,  pure,  for  titrations,  128 
Nitric  oxide  gas,  estimation  of,  466, 

473 
Nitrite,  standard  solution  of,  for  water 

analysis,  379 

Nitrites  alkaline,  titration  of,  250,  252 
Nitrites,  colorimetric  titration  of,  228 
Nitrites,  estimation  by  iodometric 

method,  250 

Nitrites,  estimated  gasometrically,  253 
Nitrites,  sulphites  and  thiosulphates, 

analysis  of  mixtures  thereof,  254 
Nitrites,  titration  of,  250 
Nitrogen  as  nitrates  and  nitrites,  224 
Nitrogen  as  nitrate,  estimation  of,  by 

copper-zinc  couple,  228,  408 
Nitrogen    combined    in    organic   sub- 
stances, 76 
Nitrogen,  estimation  of,  as  nitric  oxide, 

,    247 

Nitrogen  gas,  estimation  of,  466 
Nitrogen  in  alkaline  nitrates,  225 
Nitrogen,  indirect  estimation  of,  125 
Nitrogen,    Kjeldahl's    method    for, 

76—80 
Nitrogen,  total  in  urine,  estimation  of, 

373 

Nitrometer,  general  uses  of,  533 
Nitrometer,  Lunge's,  529 — 537 
Normal  acid  and  alkaline  solutions, 

preparation  of,  40 
Normal  acid  solutions,  verification  of, 

41 

Normal  ammonio-cupric  solution,  45 
Normal  baric  chloride,  preparation  of, 

310 
Normal  hydrochloric  acid,  43 


INDEX. 


551 


Normal  nitric  acid,  43 

Normal  oxalic  acid,  42 

Normal  potash  solution,  43 

Normal  potassic  carbonate,  42 

Normal  soda  solution,  43 

Normal  sodic  carbonate,  41 

Normal  solutions,  23 

Normal  solutions,  definition  of,  23 

Normal  solutions,  based  on  molecular 

weights,  24 

Normal  solutions  for  gases,  521 
Normal  sulphuric  acid,  42 

Oils  and  fats,  titration  equivalents  of, 

with  potash,  340 
Oils  and  fats,  titration  of,  with  bromine 

or  iodine,  340—343 
Oils  and  fats,  titration  of,  336 
Olefiant  gas,  estimation  of,  473 
Orange,  methyl,  the  proper  use  of,  33 
Orange,  methyl,  33 
Ore,  tin,  titration  of,  323 
Ores,  arsenical,  analysis  of,  139 
Ores,  copper,  technical  analysis  of,  167 
Ores,  iron,  analysis  of,  195 
Ores,  iron,  to  render  soluble,  196 
Organic  carbon  and  nitrogen  in  waters, 

384—400  > 
Organic  impurities  in  water,  estimation 

of,  without  gas  apparatus,  429 
Organic  nitrogen  and  carbon  in  waters, 

384—400 

Oxalates,  titration  of,  86 
Oxalic  acid,  normal,  42 
Oxidation  and  reduction  analyses,  105 
Oxidizing  agents,  105 
Oxygen  dissolved  in  waters,  254,  446 
Oxygen  dissolved  in  water  at  various 

temperatures,  260 
Oxygen  gag,  estimation  of,  466 
Oxygen  in  water,  estimation  of,  254—268 
Oxygen  in  waters,  Mohr's  method  of 

estimating,  255 
Oxygen  in  waters,  Winkler's  method 

of  estimating,  255 
Oxygen  in  waters,  Schutzenberger's 

method  of  estimating,  255 
Oxygen  in  waters,  Eoscoe  and  Lunt's 

method  of  estimating,  258 
Oxygen  in  waters,  iodometric  method 

of  estimating,  262 
Oxygen  process  for  water,  comparison 

with  combustion  methods,  431 
Oxygen  process  for  water,  430 

Palladium  asbestos  for  gases,  525 

Paper,  iodized  starch,  121 

Paper,  lacmoid,  35 

Paper,  litmus,  31 

Paper,  turmeric,  32 

Paper,  turmeric,  alkaline,  32 

Pavy's    copper  solution    for   sugars, 

303 

Percentages,  method  for,  26 
Permanganate,    alkaline,    for    water 

analysis,  437 


Permanganate  analyses,  calculation  of, 

109 
Permanganate  for  oxygen  process  in 

water  analysis,  438 
Permanganate  of   potash,  gasometric 

titration  of,  108 

Permanganate,  precautions  inusing,  108 
Permanganate,    preparation    of   stan- 
dard solution,  106 
Permanganate,  titration  with  double 

iron  salt,  106    . 

Permanganate,  titration  with  iron,  106 
Permanganate,  titration  of  ferric  salts 

by,  109 
Permanganate,  titration  of,  with  lead 

oxalate,  107 
Permanganate,  titration  of,  with  oxalic 

acid,  107 
Permanganate,     titration     of,      with 

hydrogen  peroxide,  108 
Permanganate,  verification  of  standard 

solution,  106 
Permanganate,  verificatioti  of  standard 

solution  by  hydrogen  peroxide,  108 
Phenacetolin,  34 
Phenacetplin,  preparation  of,  34 
Phenol,  titration  of,  348 
Phenolphthalein,  34 
Phenolphthalein,  preparation  of,  34 
Phenolphthalein,      disadvantages      in 

using,  34 

Phosphates,  earthy,  in  urine,  366 
Phosphates  in  urine,  366 
Phosphates  of  lime,  titration  of,  276 
Phosphoric  acid,  alkalimetric  titration 

of,  280 
Phosphoric  acid  in  combination  with 

alkaline  bases,  estimation  of,  274 
Phosphoric  acid  in  minerals,  estimation 

of,  279 
Phosphoric    acid,    separation    of,    for 

titration,  270 
Phosphoric  acid,  titration  of  by  molyb- 

date,  281 
Phosphoric  acid,  uranium  method  for, 

273 

Pinchcocks  for  burettes,  13 
Pipette,  the,  14 
Plate,  silver,  assay  of,  285 
Porrier's  blue,  35 
Porter-Clark  process  for  softening 

water,  429 
Potash  and  soda,  caustic,  titration  of, 

50 
Potash  and  soda,  indirect  estimation 

of,  126 

Potash  and  soda,  mixed,  57 
Potash  and  soda  in  urine,  373 
Potash,  estimation  of,  50—58 
Potash,  estimation  of  in  neutral  salts, 

free  from  soda,  55 
Potash,  estimation  of  in  presence  of 

soda,  56 

Potash  solution,  normal,  43 
Potash  in  waters,  estimation  of,  417 
Potassic  carbonate,  normal,  42 


552 


INDEX. 


Potassic  ferricyanide  as  indicator,  111 
Potassic    iodide,    how    to    free    from 

iodate,  114 
Potassic  permanganate,  preparation  of 

standard  solution,  106 
Potassic    permanganate,    titration    of 

standard  solution,  106 
Precipitates,  liquid,  for  suspending,  132 
Preservation  of  solutions,  27 
Pressure    and     temperature    in    gas 

analysis,  464 

Processes,  direct  and  indirect,  28 
Processes,  titration,  termination  of,  28 
Propylic  hydride  gas,   estimation  of, 

466 
Pump,  Sprengel,  for  water  analysis, 

390 

Pyrites,  burnt,  analysis  of,  305 
Pyrites,  estimation  of  sulphur  in,  305 

Red  liquors,  examination  of,  60 
Reduction  and  oxidation  analyses,  105 
Reduction  agents,  105 
Regnault  and  Reiset's  gas  appara- 
tus, 492 

Residual  titration,  29,  50 
Residues,  water,  combustion  of,  388 
Rosolic  acid,  35 

Sachsse's  mercuric  iodide  for  sugar, 

296 

Sal  ammoniac,  analysis  of,  71,  75 
Salt  cake,  61 
Salt  raw,  analysis  of,  63 
Salt  solution,  decinormal,  124 
Salt,  standard,  for  silver  assay,  288 
Salts,  alkaline,  titration  of,  50 
Salts,   metallic,   various,   titration  of, 

alkalimetrically,  101 
Samples  of  water,  collection  of,  381 
Saturation  analyses,  30 
Scheibler's  apparatus  for  CO2,  97 
S  chiitzenb  erg  er's  method  of  estima- 
ting oxygen  in  waters,  256 
Septem,  the,  23 

Silicates,  iron  estimated  in,  199 
Silicates  of  potash  and  soda,  titration 

of,  63 

Silver  and  chlorine  analyses,  123 
Silver  and  sulphocyanic  acid,  127 
Silver  and  thiocyanic  acid,  127 
Silver     assay,     Mulder's    improved 

method,  285 
Silver,   assay  of,  by  Gay  Lussac's 

method,  285 

Silver,  alloys,  assay  of,  286 
Silver  chromate,  solubility  of,  124 
Silver,  estimation  of,  by  standard  sodic 

chloride,  285 

Silver  plate,  assay  of,  285 
Silver  solution,  decinormal,  123 
Silver  solutions  used  in  photography, 

assay  of,  290 
Silver,  titration  of,  by  starch  iodide, 

Silver,  titration  of,  by  thiocyanate,  284 


Slags,  manganese  in,  209 

Soap,  analysis  of,  64 

Soap  solution  for  water  hardness,  380, 

438 
Soda  and  potash,  indirect  estimation 

of,  125 

Soda  and  potash  in  urine,  373 
Soda  and  potash,  mixed,  57 
Soda  and  potash  solutions,  purification 

of,  44 

Soda  ash,  titration  of,  59 
Soda  lyes,  examination  of,  60 
Soda  solution,  normal,  43 
Sodic  carbonate,  normal,  41 
Sodic  chloride,  decinormal,  124 
Sodic    hyposulphite,    Schxitzenber- 

ger's,  255,  258 
Sodic  sulphide,  titration  of,  60 
Sodic  thiosulphate  solution,  decinormal, 

preparation  of,  115 
Soldaini's  copper  solution  for  sugar, 

302 
Solids,  total  in  water,  estimation  of, 

405 

Solutions,  alkaline  and  acid,  prepara- 
tion of  normal,  40 
Solutions,   correction    of    volume    for 

temperature,  20,  21 
Solutions,  metallic  acid,  titration  of,  by 

copper,  45 

Solutions,  normal,  23,  40 
Solutions,  normal,  definition  of,  23 
Solutions,  normal,  based  on  molecular 

weights,  24 

Solutions,  preservation  of,  27 
Solutions,  standard,  correction  of,  46 
Solutions,  standard,  factors  for,  47 
Solutions,  standard,  used  by  weight, 

Soxh let's    critical    experiments    on 

sugar  titration,  297 
Spiegeleisen,  estimation  of  manganese 

in,  208 
Sprengel   pump  for  water  analysis, 

390 
Standard    alkaline    nitrite    for    water 

analysis,  379 

Standard  ammonic  molybdate,  282 
Standard  ammonic  phosphate,  275 
Standard  baryta  solution,  44 
Standard  calcic  phosphate,  277 
Standard   copper   solution   for  sugar, 

Standard  indigo  solution,  240 
Standard  potassic  phosphate,  275 
Standard  salt  solution  for  silver  assay, 

288 

Standard  silver  solution  for  water,  380 
Standard  soap  solution  for  hardness, 

380,  438 

Standard  solutions,  correction  of,  46 
Standard  solutions,  factors  for,  26,  47 
Standard  solutions  used  by  weight,  6, 

22 
Standard  water  for  hardness  (Clark's), 

414,  438 


INDEX. 


553 


Stannous  chloride  solution,  preparation 

of,  112 
Starch  and  potassic  iodide,  permanent 

solution  of,  116 

Starch,  concentrated  solution  of,  116 
Starch  indicator,  preparation  of,  116 
Starch,  inversion  of,  294 
Starch  solution,  preparation  of,  116 
Starch  paper  indicator,  121 
Starch  paste,  116 

Steel,  estimation  of  manganese  in,  209 
Strontium  in  neutral  salts,  66 
Sugar,  grape  or  glucose,  291 — 294 
Sugar  in  urine,  estimation  of,  367 
Sugar,  malt  or  maltose,  293 
Sugar,  modifications  of,  291 
Sugar  of  milk,  inversion  of,  293 
Sugar  solutions,  classification   of,   for 

analysis,  293 
Sugar  test  for  water,  445 
Sugars,  titration  of,  by  S id er sky's 

method,  301 
Sugar,  varieties  of,  291 
Sugars,    critical    experiments  on    the 

analysis  of,  297 
Sugars,  inverted  by  acid,  293 
Sugars,  mixed,  titration  of,  304 
Sugars,   various    ratios   of    reduction, 

with  Fehling's  solution,  298 
Sulphates  in  urine,  366 
Sulphides,   alkaline,   titration    of,   60, 

307—309 

Sulphides  in  alkali,  detection  of,  59 
Sulphides,  sulphites,  and  thiosulphates 

in  same  solution,  estimation  of,  309 
Sulphides,   estimation    of   sulphur  in, 

307 

Sulphites,  alkaline  titration  of,  60 
Sulphites    in    presence    of     alkalies, 

destruction  of,  54 
Sulphites,  titration  of,  308 
Sulphocarbonates,  titration  of,  349 
Sulphocyanate,  decinormal,  127 
Sulphocyanic  acid  and  silver,  127 
Sulphocyanides,  alkaline  and   earthy, 

titration  of,  177 

Sulphur  in  coal  gas,  estimation  of,  306 
Sulphur  in  pyrites,  estimation  of,  305 
Sulphur  in  sulphides,  estimation  of,  307 
Sulphuric  acid,  normal,  42 
Sulphuric  acid,  combined,  titration  of, 

310 

Sulphuric  anhydride,  titration  of,  87 
Sulphurous  acid,  ratio  of,  in  solution, 

to  specific  gravity,  309 
Sulphurous  acid,  titration  of,  308 
Sulphurous  anhydride  gas,  estimation 

of,  466 
Sulphuretted    hydrogen  in   coal    gas, 

estimation  of,  315 

Sulphuretted  hydrogen  in  water,  esti- 
mation of,  316 
Sulphuretted  hydrogen,   titration  of, 

314 

Superphosphates,  titration  of,  278 
Syringe  for  cleaning  gas  apparatus,  513 


System,  decimal,  origin  of,  18 
System  of  weights  and  measures  for 
volumetry,  18 

Tannic  acid,  titration  of,  316 

Tannin,  estimation  of,  by  antimony, 

321 
Tannin,    estimation   of,    by    gelatine, 

320 

Tannin,  titration  of,  316 
Tanning  materials,  percentage  of  tannin 

in,  320 
Tanning  materials,  preparation  of  for 

titration,  317 

Tartar  emetic,  titration  of,  134 
Tartrate  solution,  alkaline,  for  sugar, 

295 

Tartrates,  titration  of,  88 
Temperature    and    pressure    in    gas 

analysis,  464 
Temperature,   variations,  influence  of 

on  solutions,  20,  21 
Test  mixer,  17 

Thiocarbonates,  titration  of,  349 
Thiocyanate,  decinormal,  127 
Thiocyanic  acid  and  silver,  127 
Thiosulphate  and  iodine,  titration  by, 

113 
Thiosulphate  solution,  preparation  of, 

115 
Thiosulphates,  sulphides,  and  sulphites, 

mixtures  of,  309 
Thomas's  gas  apparatus,  511 
Tin,  titration  of,  321 
Tin  ore,  titration  of,  323 
Titrated  solutions,  preservation  of,  27 
Titration,  backward,  29,  50 
Titration,  residual,  29,  50 
Tourmaline,   estimation  of  boric  acid 

in,  335 

Tungsten,  titration  of,  350 
Turbidities,  estimation   of,  by  colori- 
meter, 131 

Turmeric  paper,  alkaline,  32 
Turmeric  paper,  32 
Two-foot  tube  for  water  examination, 

439 

Uranium  method  for  phosphoric  acid, 

273,  366 

Uranium  method,  Joulie's.  279 
Uranium,  standard  solution  of,  274 
Uranium,  titration  of,  323 
Urea,  titration  of,  by  hypobromite  and 

sodic  arsenite,  365 
Urea  estimation,  apparatus  for,  361 
Urea  estimations,  corrections  for,  359 
Urea,  estimation  of,  by  hypobromite, 

360 

Urea,  estimation  of,  by  mercury,  357 
Urea  estimations,  experiments  on,  363 
Urea,   Liebig's  method  of  titration. 

357 

Uric  acid,  estimation  of,  368 
Urine,  albumen  in,  estimation  of,  372 
Urine,  analysis  of,  352 


554, 


INDEX. 


Urine,  baryta  solution,  for  removing 
lates  and    sulphates    from, 


Urine,     estimation    of    chlorides    in, 

353-356 

Urine,  free  acid  in,  371 
Urine,  potash  and  soda  in,  373 
Urine,  estimation  of  total  nitrogen  in, 

373 

Vanadium,  titration  of,  332 
Variations  of  temperature,  influence 

of,  on  solutions,  20 
Vinegar,  estimation  of  mineral  acids 

in,  82 
Vinegar,     titration     of,     by     copper 

solution,  45 

Volumetric    analysis,    general    prin- 
ciples, 1 
Volumetric  and  gravimetric  analysis, 

distinction  between,  2 
Volumetric  analysis  without  weights, 

5,  6 

Volumetric  methods,  classification  of,  3 
Volumetric  methods,  various,  reasons 

for,  4 

Water  analysis,  calculation  of  results, 

448 
Water  analysis,  interpretation  of  results 

of,  419 

Water  analysis,  reagents  for,  374,  435 
Water  analysis,  table  of  results,  420 
Water  free  from  ammonia,  preparation 

Water,  hardness  of,  estimated  without 
soap  solution,  66 


Water  deposits,  microscopical  examina- 
tion of,  444 

Water  residues,  combustion  of,  388 

Water,  softening  by  Clark's  process, 
428 

Water,  sugar  test  for,  445 

Water,  estimation  of,  total  solids  in, 
405,  444 

Waters,  carbonic  acid  in,  93 

Waters  potable,  analysis  of,  373 

Weighing  standard  solutions  instead  of 
measuring,  6 

Weights  and  measures,  systematic,  for 
volumetry,  18 

Wildenstein's  filter,  313 

Williamson  and  Eussell's  gas 
apparatus,  489 

Zinc,  ammoniacal  solution,  preparation 
of,  325 

Zinc  containing  iron,  analysis  of,  330 

Zinc  dust,  analysis  of,  331 

Zinc  dust  for  reducing  ferric  com- 
pounds, 190 

Zinc  dust,  purification  of,  for  reducing 
purposes,  190 

Zinc  dust,  titration  of,  831 

Zinc,  as  ferrocyanide,  estimation  of, 
328 

Zinc  ores,  analysis  of  by  Vieille 
Montagne  method,  326 

Zinc,  as  oxalate,  estimation  of,  331 

Zinc,  as  sulphide,  titration  of,  324—327 

Zinc  oxide  and  carbonate,  analysis  of, 
332 

Zinc,  titration  of,  323—331 


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Allen.     Commercial     Organic 
Analysis.  2d  Ed.  Volume  I.  4.50 

Volume  II.  -        -          5.00 

Volume  III.     Part  I.    4.50 

Bartley.     Medical.          -          2.50 
Bloxam's  Text- Book.  7th  Ed.  4.50 
Bowman's  Practical.      -         2.00 
Groves  and  Thorp.     Chemi- 
cal Technology.  Vol.  I.  Fuels  7.50 

Holland's  Urine,  Poisons  and  • 

Milk.          ....        LOO 

Leffmann's  New  Compend.      i.oo 

,  Progressive  Exercises,  i.oo 

Muter.     Pract.  and  Anal.         2.00 

Richter's  Inorganic.    3d  Ed.   2.00 

Organic.         -         -          3.00 

Smith.     Electro-Chem.  Anal,  i.oo 
Stammer.     Problems.     -  .75 

Sutton.     Volumetric  Anal.        5.00 
Symonds.     Manual  of.  2.00 

Tidy.     Modern  Chem.  2d  Ed.  5.50 
Trimble.    Analytical.      -          1.50 
Valentin.  Qualt.  Anal.  7th  Ed.  3.00 
Watts.     (Fowne's)  Inorg.         2.25 

(Fowne's)  Organ.  2.25 

Wolff.    Applied  Medical. 
Woody.     Essentials  of. 

CHILDREN. 

Chavasse.  Mental  Culture  of.  i.oo 
Day.  Diseases  of.  -  -  3.00 
Dillnberger.  Women  and.  1.50 
Goodhart  and  Starr.  3.00;  Sh.  3.50 
Hale.  Care  of.  -  .75 

Hatfield.    Compend  of.  i.oo 

Meigs.      Infant  Feeding    and 

Milk  Analysis.  -          i.oo 

Meigs  and  Pepper's  Treatise. 5.00 
Money.  Treatment  of.  -  3  oo 
Osier.  Cerebral  Palsies  of.  2.00 
Smith.  Wasting  Diseases  of.  3.00 

Clinical  Studies.  -          2.50 

Starr.  Digestive  Organs  of.  2.50 
-Hygiene  of  the  Nursery,  i.oo 


i.oo 
1.25 


CLINICAL  CHARTS. 
Davis.     Obstetrical.     Pads,    $  .50 
Griffiths.     Graphic.  .50 

Temperature  Charts.    "          .50 

COM  PEN  DS 
And  The  Quiz-Compends. 
Ballou.  Veterinary  Anat.  i.oo 
Brubaker's  Physiol.  sth  Ed.  i.oo 
Fox  and  Gould.  The  Eye.  i.oo 
Hatfield.  Children.  -  i.oo 
Horwitz.  Surgery.  3d  Ed.  i.oo 
Hughes.  Practice.  2  Pts.  Ea.  i.oo 
L-andis.  Obstetrics.  4th  Ed.  i.oo 
Leffmann's  Chemistry.  3d  Ed.  i.oo 
Mason.  Electricity.  -  i.oo 
Morris.  Gynaecology.  -  i.oo 
Potter's  Anatomy,  4th  Ed.  i.oo 

Materia  Medica.  sth  Ed.  i.oo 

Roberts.  Mat.  Med.  and  Phar.  2.00 
Stewart,  Pharmacy.  2d  Ed.  i.oo 
Warren.  Dentistry.  -  i.oo 

DEFORMITIES. 
Churc.hill.     Face  and  Foot.      3.50 
Coles.    Of  Mouth.  -         4.50 

Prince.  Orthopaedics.  -  4.50 
Reeves.  -  2.25 

Roberts.    Club-foot.       -  .50 

DENTISTRY. 

Barrett.  Dental  Surg.  -  1.25 
Blodgett.  Dental  Pathology.  1.75 
Flagg.  Plastic  Filling.  -  4.00 
Fillebrown.  Op.  Dent.  lllus.  2.50 
Gorgas.  Dental  Medicine.  3.50 
Harris.  Principles  and  Prac.  7.00 

Dictionary  of.       -          6.50 

Heath.     Dis.  of  Jaws.     -         4.50 

Lectures  on  Jaws.  Bds.  i.oo 

Leber    and    Rottenstein. 
Caries.      Paper  75  ;  Cloth 
Richardson.     Mech.  Dent. 
Sewell.     Dental  Surg. 
Stocken.     Materia  Medica. 


1-25 
4-5o 
3.00 
2.50 
4-25 

2.OO 

Talbot.  Irregularity  of  Teeth.  3.00 


Taft.    Operative  Dentistry. 
-,  Index  of  Dental  Lit. 


5-00 

4.00 

i.oo 

.50 


Tomes.     Dental  Surgery. 

Dental  Anatomy. 

Warren's  Compend  of.     - 
White.    Mouth  and  Teeth. 
DICTIONARIES. 
Cleveland's  Pocket  Medical.     .75 
Gould's  New  Medl.    ft  Lea.,      ' 

3.25;  y2  M.  Thumb  Index.  4.25 
Harris' Dental.  Clo.  6. 50;  Shp.  7.50 
Longley's  Pronouncing  -  i.oo 
Maxwell.  Terminologia  Med- 
ica Polyglotta.  -  -  4.00 
Treves.  German  English.  3-75 

DIRECTORY. 
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EAR. 

Burnett.     Hearing,  etc.  .50 

Jones.  Aural  Surgeiy.  -  2.75 
Pritchard.  Diseases  of.  1.50 

ELECTRICITY. 
Althaus'  Text  Book.         -        6.00 
Mason's  Compend.  -        i.oo 

EYE. 

/rlt.  Diseases  of.  -  -  2.50 
Fox  and  Gould.  Compend.  i.oo 
Gower's  Ophthalmoscopy.  5.50 
Harlan.  Eyesight.  .50 

Hartridge.  Refraction.  4thEd.  2.00 
Higgins.  Practical  Manual.  1.75 
— — ^  Handbook,  -  .50 

Liebreich.    Atlas  of  Ophth.    15.00 


.50 

I.OO 

•50 
•50 
•50 
-50 

•75 

•5° 
•50 


Macnamara.     Diseases  of.     $ 

Meyer  and    Fergus.      Com- 
plete Text-Book,  with  Colored 
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Monthly.  -          3.00 

Swanzy's  Handbook,  sd  Ed.  3.00 

FEVERS. 

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HEADACHES. 

Day.     Their  Treatment,  etc.     1.25 
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Bulkley.    The  Skin.        -  .50 

Burnett.     Hearing.          -  .50 

Cohen.  Throat  and  Voice.  .50 
Dulles.  Emergencies.  3d  Ed.  .75 
Harlan.  Eyesight.  -  .50 

Hartshorne.    Our  Homes. 
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Lincoln.     Hygiene. 
Osgood.     Dangers  of  Winter. 
Packard.    Sea  Air,  etc. 
Richardson's  Long  Life. 
Tanner.     On  Poisons. 
White.     Mouth  and  Teeth. 
"Wilson.     Summer  and  its  Dis 
Wilson's  Domestic  Hygiene,  i.oo 
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HEART. 

Fothergill.  Diseases  of.  3.50 
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HISTOLOGY. 
See  Microscope  and  Pathology. 

HYGIENE. 

Frankland.  Water  Analysis,  i.oo 
Fox.  Water,  Air,  Food.  4.00 

Lincoln.  School  Hygiene.  .50 
Parke's  (E.)  Hygiene.  7th  Ed.  4.50 

(L.  C.),  Manual.  2.50 

Starr.  H  yidene  of  the  Nursery,  i.oo 
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JOURNALS,  ETC. 
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Ophthalmic  Review.  "  '  3.00 
New  Sydenham  Society's 

Publications     -  9.00 

KIDNEY  DISEASES. 
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Edwards.     How  to  Live  with 

Bright's  Disease.    -         -  .50 

Ralfe.  Dis.  of  Kidney,  etc.  2.75 
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Tyson.  Bright's  Disease 

and  Diabetes,  lllus.          -        3.50 

LIVER. 

Habershon.  Diseases  of.  1.50 
Harley.  Diseases  of.  -  3.00 

LUNGS  AND  CHEST. 

See  Phy.  Diagnosis  and  Throat. 

Hare.     Mtdiastinal  Disease.     2.00 

Harris.     On  the  Chest.   -          2.50 

Williams.     Consumption.        5.00 

MASSAGE. 

Murrell.  Massage.  5th  Ed.  1.50 
Ostrom.  Massage,  lllus.  .75 

MATERIA  MEDICA. 
Biddle.     nth  Ed.  Clo.  4.25 

Gorgas.  Dental.  3d  Ed.  3.50 
Merrell's  Digest.  -  4.00 

Potter's  Compend  of.  5th  Ed.  i.oo 


CLASSIFIED  LIST  OF  P.  BLAK1STON,  SON  &  CO.'S  PUBLICATIONS. 


Potter's  Handbook  of.  Second 

Ed.    Clo.  4.00 ;  Sheep,     -      $5.00 
Roberts'  Compend  of.  z.co 

MEDICAL  JURISPRUDENCE. 
Reese.  Medical  Jurisprudence 

&Toxicology,  2d  Ed.  3.oc;Sh  3.50 

MICROSCOPE. 
Beale.     How  to  Work  with.     7.50 

In  Medicine.         -          7.50 

Carpenter.     The  Microscope. 

Lee  Vade  Mecum  of.  2<l  Ed.  4.00 
MacDonald.  Examination  of 

Water  by.        -        -         -  2.75 

Wythe.     The  Microscopist.     3.00 

MISCELLANEOUS. 
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Beale.      Slight  Ailments.  1.25 

Black.  Micro-organisms.  1.50 
Crookshank.  Vaccination.  8.50 
Davis.  Text-book  of  Biology.  4.00 
Duckworth.  On  Gout.  -  700 
Edwards.  Vaccination.  .50 

Garrod.  Rheumatism,  etc.  6.00 
Gross.  Life  of  John  Hunter.  1.25 
Had  don.  Embryology.  -  6.00 
Henry.  Anaemia.  -  .75 

Keating.  Life  Insurance.  Net,  2.00 
MacMunn.  The  Spectroscope  3.00 
Madden.  Health  Resorts.  2  50 

.NERVOUS  DISEASES,  Etc. 
Flower.    Atlas  of  Nerves.         3.50 
Bowlby.     Injuries  of.        -        4.50 
Gowers.    Manual  of.     i  vol. 

341  Illustrations. 
Dis.  of  Spinal  Cord.      

Diseases  of  Brain.          2.00 

Syphilis  and  the  Ner- 
vous System.          -        -          

Oberstemer.   Central  Nervous 

System.    -  6.00 

Osier.     Cerebral  Palsies.  2.00 

Page.     Injuries  of  Spine.          

Radcliffe.  Epilepsy,  Pain,  etc.  1.25 
Thorburn.  Surgery  of  the 

bpinal  Cord    -  4'5° 

Watson.     Concussions.  i.oo 

NURSING. 
Cullingworth.    Manual  of. 

Monthly    Nursing. 

Domville's  Manual.     6th  Ed 
Fullerton.     Obst.  Nursing. 
Humphrey.     Manual  of 


.75 
.50 
.75 
1.25 
1.25 
i.oo 
.75 


Luckes.  Hospital  Sisters. 
Parvin.     Obstetric  Nursing. 
Starr.  Hygiene  ot  the  Nursery,  i.oo 
Temperature  Charts.    -  .50 

OBSTETRICS. 

Bar.     Antiseptic  Obstet.  1.75 

Barnes.  Obstetric  Operations.  3.75 
Cazeaux  and  Tarnier.  Stu- 

dents'   Ed.     Colored  Plates.  5.00 
Davis.     Obstetrical  Chart.  .50 

'Galabin's  Manual  of.  3.00 

Glisan's  Text-book.  2d  Ed.  4.00 
Landis.  Compend.  4  h  Ed.  i.oo 
Meadows.  Manual.  -  2.00 
Rigby.  Obstetric  Mem.  .50 

Strahan.  Extra-Uterine  Preg.  1.50 
Tyler  Smith's  Treatise.  4.00 

Sway  ne's  Aphorisms  gth  Ed.  1.25 
Winckel's  Text-book.  6.00 

PATHOLOGY  &  HISTOLOGY. 
Blodgett.  Dental  Pathology  1.75 
Bowlby.  Surgical  Path.  2.00 

Gibbes.    Practical.  -          1.75 

Gilliam.  Essentials  of.  -  2.00 
Stirling's  Practical.  -  4.00 
Virchow.  Post-mortems.  i.oo 
-  Cellular  Pathology.  4.00 
Wynter&  Wethered.  Path.  4.00 

PHARMACY. 

Beasley's  Druggists'  Rec'ts.  2.25 
--  Formulary.  -  -  2.25 

Fliickiger.  Cinchona  Barks.  1.50 
Kirby.  Pharm.  ot  Remedies.  2.25 
Mackenzie.  Phar.  of  Throat.  1.25 


Merrell's  Digest.  -  -  $\.oo 
Proctor.  Practical  Pharm.  4.50 
Robinson.  Latin  Grammar  of.  2.00 
Stewart's  Compend.  2d  Ed.  i.oo 
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PHYSIOLOGY. 
Brubaker's  Compend.     Illus- 
trated.    4th  Ed.      -        -          i.oo 
Kirkes'   i2th   Ed.     (Author's 

Ed.)          Cloth,  4.00;   Sheep,  5.00 
Landois'  Text-book.  583  Illus- 
trations.    2d  Ed.      -        -        6.50 
Sanderson's  Laboratory  B'k.  5.00 
Sterling.    Practical  Phys.        2.25 
Tyson's  Cell  Doctrine.    -          2.00 
Yeo's  Manual.  321  Illustrations 
4th  Ed     Cloth,  3.00;  Sheep,  3.50 

POISONS. 

Aitken.  The  Ptomaines,  etc.  1.25 
Black.  '  Formation  of.  -  i  50 

Reese.  Toxicology.  2d  Ed.  3.00 
Tanner.  Memoranda  of.  .7^ 

PRACTICE. 

Beale.     Slight  Ailments.  1.25 

Fagge's  Practice.     2  Vols.       8.00 
Fenwick's  Outlines  of.    -          1.25 
Fowler's  bict'onary  of. 
Hughes.  Compend  of.   2  Pts.  2.00 

Physicians'  Edition. 

i  Vol.  Morocco,  Gilt  edge.  2.50 
Roberts.  Text-book,  bth  Ed.  5.50 
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Taylor's  Manual  of.  -  4  oo 

PRESCRIPTION  BOOKS. 
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Bulkley.    The  Skin.         -  .50 

Crocker.    Dis,  of  Skin.   Illus.  5.50 
Van   Harlingen.      Diagnosis 
;md  Treatment  of  Skin  Dis. 
Col.  Plates  &  Engravings.       2.50 
STIMULANTS  &  NARCOTICS. 
Lizars.     On  Tobacco.      -  .50 

Miller.     On  Alcohol  .50 

Parrish.     Inebriety.         -         1.25 
SURGERY  AND  SURGICAL 

DISEASES. 

Caird  and  Cathcart.     Surgi- 
cal Handbook.  Leather,  2.50 
Dulles.     Emergencies.         -        .75 
Heath's  Operative.  -        12.00 
Minor.    9th  Ed.      -          2.00 

Diseases  of  Jaws.  4.50 

Lectures  on  Jaws.  i.oo 


Field.  Cathartics  and  Emetics  $1.75 
Headland.  Action  of  Med.  3.00 
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.  Theine  -  -  -  50 
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Potter's  Compend.  5th  Ed.  i.oo 
.Handbook  of.  4.00  ;  Sh.  5.00 


Horwitz.  Compend.  3d  Ed.  i.oo 
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Porter's  Surgeon's  Pocket- 

book.  -         -    Leather.  2.25 

Roberts.     (A.  S.)  Club-Foot.     .50 
(A.  S.)    Bow-  Legs.  .50 


Smith.     Abdominal  Surg.  7.00 

Swain.     Surg.  Emergencies.  1.50 

Walsham.     Practical  Surg.  3  oo 

Watson's  Amputations.  5.50 

TECHNOLOGICAL  BOOKS. 

See  also  Chemistry. 
Cameron.     Oils  &  Varnishes.  2.50 

-  Soap  and  Candles.          2.25 
Gardner.     Brewing,  etc.  1.75 
Gardner.     Acetic  Acid,  etc.      1.75 

-  Bleaching  &  Dyeing.     1.75 
Groves  and  Thorp.    Chemi- 

cal   Technology.       Vol.     I. 

Mills  on  Fuels.  Cl.  7.50;  J^M.  9.00 
Overman.     Mineralogy.  i.oo 

Piggott.     On  Copper.      -          i.oo 

THERAPEUTICS. 
Biddle.  nth  Ed.  Cl.  4.25;  Sh.    5.00 
Cohen.     Inhalations.        -          1.25 


Starr,  Walker  and  Powell. 

Phys.  Action  ot  Medicines.        .75 
Waring's  Practical.    4th  Ed.  3.00 

THROAT  AND  NOSE. 
Cohen.     Throat  and  Voice.         .50 

Inhalations.  -  1.25 

Greenhow.     Bronchitis.  I-25 

James.     Sore  Throat        -  1.25 

Journal  of  Laryngology.        3.00 
Mackenzie.  The  Oesophagus, 

Naso-Pharynx,  etc.          -          3.00 

Pharmacopoeia.    -          1.25 

Murrell.  Bronchitis.  -  i  50 
Potter.  Stammering,  etc.  i.oo 
Woakes.  Post-Nasal  Catarrh.  1.50 

Nasal  Polypus,  etc.  1.25 

Deafness,  Giddiness,  etc. 

TRANSACTIONS   AND 

REPORTS. 

Penna.  Hospital  Reports.  1.25 
Power  and  Holmes'  Reports.  1.25 
Trans.  College  of  Physicians.  3.50 
Amer.  Surg.  Assoc.  3.00 

Assoc.  Amer.  Phys.   3.50 

URINE  &  URINARY  ORGANS. 
Acton.     Repro.  Organs.  2.00 

Beale.     Urin.  &  Renal  Dis.      1.75 

Urin.  Deposits.    Plates.  2.00 


Holland.  The  Urine  and  Com- 
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L-egg.     On  Urine.     -         -  .75 

MacMunn.  Chem.  of  Urine,  3.00 
Marshall  and  Smith.  Urine,  i.oo 
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Schnee.  Diabetes.  -  2.00 

Thompson.  Urinary  Organs.    3.50 

Surg.  of  Urin.  Organs.    1.25 

Calculous  Dis.  3d.  Ed.    i.oo 

Lithotomy.     -        -          3-50 
Prostate.     6th  Ed.  2.00 


Thornton.  Surg.  of  Kidney.  1.75 
Tyson.  Exam,  of  Urine.  1.50 
Van  Niiys.  Urine  Analysis.  2.00 

VENEREAL  DISEASES. 
Cooper.    Syphilis.  -        -         3.50 
Durkee.     Gonorrhoea.     -          3.50 
Hill  and  Cooper's  Manual,    i.oo 
Lewin.     Syphilis.  Pa  75;  Clo.  1.25 

VETERINARY. 
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VISITING  LISTS. 
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Frankland.  Analysis  of.  i.oo 
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WOMEN,  DISEASES  OF. 
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Uterus.  -        -         -          1.25 

Dillnberger.  and  Children.  1.50 
Doran.  Gynaec.  Operations.  4.50 
Edis.  Sterility.  -  -  1.75 
Lewers.  Dis.  of  Women.  2.25 
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FROM  PROF.  J.  M.  DACOSTA. 

"  I  find  it  an  excellent  -work,  doing  credit  to  tlie  learning  and  discrimination  of  the  author. 

A  NEW  MEDICAL  DICTIONARY 


A  compact,  concise  Vocabulary,  including 
all  the  Words  and  Phrases  used  in  medicine, 
with  their  proper  Pronunciation  and  Defini- 
tions. 

BASED  ON  RECENT  MEDICAL 
LITERATURE. 


GEORGE  M.  GOULD,  A.B.,  M.D., 

Ophthalmic  Surgeon  to  the  Philadelphia  Hospital,  Clinical 
Chief  Ophthalmolo    ' 


pital, 


Dept.   German  Hos- 
^hiladelphia. 


Small   8vo,  Half  Morocco,  as  above, 
Thumb  Inde> 


$4.25 


It  is  not  a  mere  compilation  from  other 
dictionaries.  The  definitions  have  been 
made  by  the  aid  of  the  most  recent  stan- 
dard text-books  in  the  various  branches  of 

Plain  Dark  Leather,  without  Thumb  Index,    3.25    medicine.       It  includes 

SEVERAL  THOUSAND  NEW  WORDS  NOT  CONTAINED  IN 
ANY   SIMILAR  WORK. 

IT  CONTAINS  TABLES  of  the  ABBREVIATIONS  used  in  Medicine,  of  the 
ARTERIES,  of  the  BACILLI,  giving  the  Name,  Habitat,  Character  sties,  etc.;  of  GAN- 
GLIA/LEUCOMAINES,  MICROCOCCI,  MUSCLES,  NERVES,  PLEXUSES, 
PTOMAINES,  with  the  Name,  Formula,  Physiological  Action,  etc.;  and  the  COMPARI- 
SON OF  THERMOMETERS,  of  all  the  most  used  WEIGHTS  AND  MEASURES 
of  the  world,  of  the  MINERAL  SPRINGS  OF  THE  U.  S.,  VITAL  STATISTICS, 
etc.  Much  of  the  material  thus  classified  is  not  obtainable  by  English  readers  in  any  other  work. 

OPINIONS  OF  PROMINENT  MEDICAL  TEACHERS. 


<;  The  compact  size  of  this  dictionary,  its 
clear  type,  and  its  accuracy  are  unfailing 
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S.  Marine  Hospital  Service,  Washington. 

•'  It  is  certainly  as  convenient  and  as  useful  a 
volume  as  can  be  found,  regarding  contents  as 
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—E.  H.  Bartlev,  Prof,  of  Chemistry,  Long 
Island  College  Hospital,  Brooklyn. 

"  I  consider  this  the  dictionary  of  all  others 
for  the  medical  student,  and  shall  see  that  it  is 
placed  on  our  list  of  text-books." — A.  R. 
Thomas,  M.D.,  Dean  Hahnemann  Medl.  Col., 
Philadelphia. 


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books in  our  new  catalogue.'' — S.  E.  Chaille, 
M.D.,  Dean  Medl.  Dept.,  Tulane  Univ.,  New 
Orleans. 

"  Compact,  exact,  up  to  date,  and  the  tables 
are  most  excellent  and  instructive.  I  prefer  it 
to  the  larger  and  older  books." — Prof.  C.  B. 
Parker,  Medl.  Dept.,  Western  Reserve  Univ., 
Cleveland. 

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hensive as  to  the  number  of  words,  including 
those  of  the  latest  coinage,  and  concise  in  its 
definitions.  The  etymology  and  accentuation 
materially  enhance  its  value,  and  help  to  make 
it  worthy  a  place  with  the  classical  books  of 
reference  for  medical  students." — J.  W.  Hol- 
land, M.D  ,  Dean  Jefferson  Medl.  Col.,  Phila. 


May  be  obtained  through  all  Booksellers.     Sample  pages  free. 


P.  BLAKISTON,  SON  &  CO.'S 

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ACTON.  The  Functions  and  Disorders  of  the  Reproductive  Organs  in  Childhood, 
Youth,  Adult  Age  and  Advanced  Life,  considered  in  their  Physiological,  Social 
and  Moral  Relations.  By  WM.  ACTON,  M.D.,  M.R.C.S.  ;th  Edition.  Cloth,  $2.00 

AITKEN.  Animal  Alkaloids,  the  Ptomaines,  Leucomaines  and  Extractives  in 
their  Pathological  Relations.  A  short  summary  of  recent  researches  as  to  the 
origin  of  some  diseases  by  or  through  the  physiological  processes  going  on 
during  life.  By  WILLIAM  AITKEN,  M.D.,  F.R.S.,  Professor  of  Pathology  in  the 
Army  Medical  School,  Netley,  England.  2nd  Ed.  Enlarged.  .Cloth,  $1.25 

ALLEN.    Commercial  Organic  Analysis.    A  Treatise  on  the  Modes  of  Assaying 
the  Various  Organic  Chemicals  and  Products  employed  in  the  Arts,  Manufactures, 
Medicine,  etc.,  with  Concise  Methods  for  the  Detection  of  Impurities,  Adultera- 
tions, etc.     Second  Edition.    Revised  and  Enlarged.    By  ALFRED  ALLEN,  F.C.S. 
Vol.    I.    Alcohols,    Ethers,   Vegetable    Acids,    Starch   and    its   Isomers.   etc. 

Out  of  Print. 

Vol.  II.  Fixed  Oils  and   Fats,  Hydrocarbons  and  Mineral  Oils,  Phenols  and 

their  Derivatives,  Coloring  Matters,  etc.  Out  of  Print. 

Vol.  III.— Part  I.    Acid   Derivatives   of  Phenols,  Aromatic   Acids,  Tannins, 

Dyes,  and  Coloring  Matters.     8vo.  Cloth,  $4.50 

ANDERSON.  A  Treatise  on  Skin  Diseases.  With  special  reference  to  Diagnosis 
and  Treatment,  and  including  an  Analysis  of  11,000  consecutive  cases.  By  T. 
McCALL  ANDERSON,  M.D.,  Professor  of  Clinical  Medicine,  University  of  Glasgow. 
With  several  Full-page  Plates,  two  of  which  are  Colored  Lithographs,  and  nu- 
merous Wood  Engravings.  Octavo.  650  pages.  Cloth,  $4.50;  Leather,  $5.50 

ARCHIVES  OF  SURGERY.  Edited  by  JONATHAN  HUTCHINSON,  F.R!S.  Colored 
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ARLT.  Diseases  of  the  Eye.  Clinical  Studies  on  Diseases  of  the  Eye.  Including  the 
Conjunctiva,  Cornea  and  Sclerotic,  Iris  and  Ciliary  Body.  By  Dr.  FERD.  RITTER 
VON  ARLT,  University  of  Vienna.  Authorized  Translation  by  LYMAN  WARE, 
M.D.,  Surgeon  to  the  Illinois  Charitable  Eye  and  Ear  Infirmary,  Chicago. 
Illustrated.  8vo.  Cloth,  $2.50 

ARMATAGE.  The  Veterinarian's  Pocket  Remembrancer :  being  Concise 
Directions  for  the  Treatment  of  Urgent  or  Rare  Cases,  embracing  Semeiology, 
Diagnosis,  Prognosis,  Surgery,  Therapeutics,  Toxicology,  Detection  of  Poisons 
by  their  appropriate  tests,  Hygiene,  etc.  By  GEORGE  ARMATAGE,  M.R.C.V.S. 
Second  Edition,  321110.  Boards,  $1.25 

BALLOT!.  Veterinary  Anatomy  and  Physiology.  By  WM.  R.  BALLOU,  M.D., 
Prof,  of  Equine  Anatomy,  New  York  College  of  Veterinary  Surgeons,  Physician 
to  Bellevue  Dispensary,  and  Lecturer  on  Genito-Urinary  Surgery,  New  York 
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BAR.  Antiseptic  Midwifery.  The  Principles  of  Antiseptic  Methods  Applied  to 
Obstetric  Practice.  By  Dr.  PAUL  BAR,  Obstetrician  to,  formerly  Interne  in,  the 
Maternity  Hospital,  Paris.  Authorized  Translation  by  HENRY  D.  FRY,  M.D. 
with  an  Appendix  by  the  author.  Octavo.  Cloth,  $1.75 

BARNES.  Lectures  on  Obstetric  Operations,  including  the  Treatment  of  Hemor- 
rhage, and  forming  a  Guide  to  Difficult  Labor.  By  ROBERT  BARNES,  M.D. 
F.R.C.P.  Fourth  Edition.  Illustrated.  8vo.  Cloth,  $3.75 

BARRETT.  Dental  Surgery  for  General  Practitioners  and  Students  of  Medicine 
and  Dentistry.  Extraction  of  Teeth,  etc.  By  A.  W.  BARRETT,  M.D.  Second 
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5 


P.  BLAKISTON,  SON  6-  CO:S 


HARTLEY.  Medical  Chemistry.  Second  Edition.  A  Text-book  for  Medical  and 
Pharmaceutical  Students.  By  E.  H.  BARTLEY,  M.D.,  Professor  of  Chemistry  and 
Toxicology  at  the  Long  Island  College  Hospital ;  President  of  the  American 
Society  of  Public  Analysts;  Chief  Chemist,  Board  of  Health,  of  Brooklyn.  N.Y. 
Revised  arid  enlarged.  With  62  Illustrations.  Glossary  and  Complete. Index. 
423  pages.  I2mo.  Cloth,  $2.50 

BEALE.  On  Slight  Ailments ;  their  Nature  and  Treatment.  By  LIONEL  S.  BEALE, 
M.D.,  F.R.S.,  Professor  of  Practice,  King's  Medical  College,  London.  Second 
Edition.  Enlarged  and  Illustrated.  8vo.  Cloth,  $1.25 

Urinary  and  Renal  Diseases  and  Calculous  Disorders.    Hints  on  Diagnosis 
and  Treatment.     Demi-8vo.     356  pages.  Cloth,  $1.75 

The  Use  of  the  Microscope  in  Practical  Medicine.    For  Students  and 
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in   the  Microscope.     Fourth  Edition.     500  Illustrations.     8vo.     Cloth,  $7.50 
Howto  Work  with  the  Microscope.    A  Complete  Manual  of  Microscopical 
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investigation,   with    directions    for    examining   objects   under  the    highest 
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Containing  over  400  Illustrations,  many  of  them  colored.     8vo.    Cloth,  $7.50 
One  Hundred  Urinary  Deposits,  on  eight  sheets,  for  the  Hospital,  Labora- 
tory, or  Surgery.     New  Edition.     410.  Paper,  $2.00 
BEASLEY'S  Book  of  Prescriptions.    Containing  over  3100  Prescriptions,  collected 
from  the   Practice   of  the   most  Eminent  Physicians  and   Surgeons — English, 
French  and  American;  a  Compendious  History  of  the  Materia  Medica,  Lists  of 
the  Doses  of  all  Officinal  and  Established  Preparations,  and  an  Index  of  Diseases 
and  their  Remedies.     By  HENRY  BEASLEY.     Sixth  Edition.  Cloth,  #2.25 
Druggists'  General  Receipt  Book.     Comprising  a  copious  Veterinary  Formu- 
lary ;  Recipes  in   Patent  and   Proprietary  Medicines,  Druggists'  Nostrums, 
etc.;    Perfumery  and  Cosmetics  ;  Beverages,   Dietetic  Articles  and  Condi- 
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Tables.     Ninth  Edition.     Revised.  Cloth,  $2.25 
Pocket  Formulary  and  Synopsis  of  the  British  and  Foreign  Pharmacopoeias. 
Comprising  Standard  and  Approved  Formulae  for   the    Preparations   and 
Compounds  Employed  in  Medical  Practice.    Eleventh  Edition.    Cloth,  $2.25 
BIDDLE'S  Materia  Medica  and  Therapeutics.    Eleventh  Edition.    For  the  Use  of 
Students  and  Physicians.     By  Prof.  JOHN  B.  BIDDLE,  M.D..  Professor  of  Materia 
Medica  in  Jefferson  Medical  College,  Philadelphia.     The  Eleventh  Edition,  thor- 
oughly revised,  and  in  many  parts  rewritten,  by  his  son,  CLEMENT  BIDDLE,  M.D., 
Assistant  Surgeon,  U.   S.  Navy,  and  HENRY  MORRIS,  M.D.,  Demonstrator  of 
Obstetrics  in  Jefferson  Medical  College,  Fellow  of  the  College  of  Physicians,  of 
Philadelphia,  etc.                                                                Cloth,  $4.25;  Sheep,  #5.00 
BLACK.     Micro-Organisms.     The  Formation  of  Poisons  by  Micro-Organisms.     A 
Biological  study  of  the  Germ  Theory  of  Disease.     By  G.  V.  BLACK,  M.D.,  D.D.S. 

Cloth,  $1.50 

BLODGETT'S  Dental  Pathology.  By  ALBERT  N.  BLODGETT,  M.D.,  Late  Profes- 
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"mo.  Cloth,  $1.75 

BLOXAM.  Chemistry,  Inorganic  and  Organic.  With  Experiments.  By 
CHARLES  L.  BLOXAM.  Edited  by  J.  M.  THOMPSON,  Professor  of  Chemistry  in 
King's  College,  London,  and  A.  G.  BLOXAM,  Dem.  of  Chem.,  Royal  Agricultural 
College,  Cirencester.  Seventh  Edition.  Revised  and  Enlarged.  With  330 
Engravings.  8vo.  Cloth,  $4.50;  Leather,  $5.50 

BOWLBY.    Injuries  and  Diseases  of  the  Nerves,  and  their  surgical  treatment. 
•  By  ANTHONY  A.  BOWLBY,  F.R.C.S.,  Surgical  Registrar  and   Demonstrator   of 
Practical  Surgery  at  St.  Bartholomew's  Hospital.     Illustrated  by  4  Colored  and 
20  other  full-page  plates.     8vo.  Cloth,  $4.50 

Surgical  Pathology  and  Morbid  Anatomy.     135  Illustrations.   Cloth,  $2.00 


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BOWMAN.  Practical  Chemistry,  including  analysis,  with  about  ioo  Illustrations. 
By  Prof.  JOHN  E.  BOWMAN.  Eighth  English  Edition.  Revised  by  Prof.  BLOXAM, 
Professor  of  Chemistry,  King's  College,  London.  Cloth,  $2.00 

BRUBAKER.  Physiology.  A  Compend  of  Physiology,  specially  adapted  for  the 
use  of  Students  and  Physicians.  By  A.  P.  BRUBAKER,  M.D.,  Demonstrator  of 
Physiology  at  Jefferson  Medical  College,  Prof,  of  Physiology,  Penn'a  College  of 
Dental  Surgery,  Philadelphia.  Fifth  Edition.  Revised,  Enlarged  and  Illus- 
trated. No.  4,? 'Quiz- Compend  Series?  I2ino.  Cloth,  $1.00 

Interleaved  for  the  addition  of  notes,  $1.25 

BUCKNILL  AND  TTJKE'S  Manual  of  Psychological  Medicine :  containing 
the  Lunacy  Laws,  the  Nosology,  ^Etiology,  Statistics,  Description,  Diagnosis, 
Pathology  (including  morbid  Histology)  and  Treatment  of  Insanity.  By  JOHN 
CHARLES  BUCKNILL,  M.D.,  F.R.S.,  and  DANIEL  HACK  TUKE,  M.D.,  F.R.C.I-. 
Fourth  Edition.  Numerous  illustrations.  8vo.  Cloth,  $8.00 

BTILKLEY.  The  Skin  in  Health  and  Disease.  By  L.  DUNCAN  BULKLEY,  M.D., 
Attending  Physician  at  the  New  York  Hospital.  Illustrated.  Cloth,  .50 

BTJXTON.  On  Anaesthetics.  A  Manual.  By  DUDLEY  WILMOT  BUXTON,  M.R.C.S., 
M.R.C.P.,  Asst.  to  Prof,  of  Med.,  and  Administrator  of  Anaesthetics,  University 
College  Hospital,  London.  Practical  Series.  {Seepage  igJ]  Cloth,  $1.25 

BURNETT.  Hearing,  and  How  to  Keep  It.  By  CHAS.  H.  BURNETT,  M.D.,  Prof, 
of  Diseases  of  the  Ear,  at  the  Philadelphia  Polyclinic.  Illustrated.  Cloth.  .50 

BYFORD.  Diseases  of  Women.  The  Practice  of  Medicine  and  Surgery,  as 
applied  to  the  Diseases  and  Accidents  Incident  to  Women.  By  W.  H.  BYFORD, 
A.M.,  M.D.,  Professor  of  Gynaecology  in  Rush  Medical  College  and  of  Obstetrics 
in  the  Woman's  Medical  College;  Surgeon  to  the  Woman's  Hospital ;  Ex-Presi- 
dent American  Gynaecological  Society,  etc.,  and  HENRY  T.  BYFORD,  M.D.,  Sur- 
geon to  the  Woman's  Hospital  of  Chicago;  Gynaecologist  to  St.  Luke's  Hos- 
pital ;  President  Chicago  Gynaecological  Society,  etc.  Fourth  Edition.  Revised, 
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Octavo.  832  pages.  Cloth,  $5.00  ;  Leather,  $6.00 

On  the  Uterus.     Chronic  Inflammation  and  Displacement.  Cloth,  $1.25 

CAIRD  and  CATKCART.  Surgical  Handbook  for  the  use  of  Practitioners  and 
Students.  By  F.  MITCHELL  CAIRO,  M.B.,  F.R.C.S.,  and  C.  WALKER  CATHCART, 
M.B.,  F;R.C.S.,  Asst.  Surgeons  Royal  Infirmary.  With  over  200  Illustrations. 
32mo.  400  pages.  Pocket  size.  Leather  covers,  $2.50 

CAMERON.  Oils  and  Varnishes.  A  Practical  Handbook,  by  JAMES  CAMERON, 
F.i.C.  With  Illustrations,  Formulae,  Tables,  etc.  I2mo.  Cloth,  #2.50 

Soap  and  Candles.  A  New  Handbook  for  Manufacturers,  Chemists,  Ana- 
lysts, etc.  Compiled  from  all  reliable  and  recent  sources.  54  Illustrations. 
I2mo.  Cloth,  $2.25 

CARPENTER.  The  Microscope  and  Its  Revelations.  By  W.  B.  CARPENTER, 
M.D.,  F.R.S.  Seventh  Edition.  Revised  and  Enlarged,  with  over  500  Illustra- 
tions and  Lithographs.  New  Edition  in  Press. 

CAZEAUX  and  TARNIER'S  Midwifery.  With  Appendix,  by  Munde.  Eighth 
Revised  and  Enlarged  Edition.  With  Colored  Plates  and  numerous  other 
Illustrations.  The  Theory  and  Practice  of  Obstetrics  ;  including  the  Diseases 
of  Pregnancy  and  Parturition,  Obstetrical  Operations,  etc.  By  P.  CAZEAUX, 
Member  of  the  Imperial  Academy  of  Medicine,  Adjunct  Professor  in  the  Faculty 
of  Medicine  in  Paris.  Remodeled  and  rearranged,  with  revisions  and  additions, 
by  S.  TARNIER,  M.D.,  Professor  of  Obstetrics  and  Diseases  of  Women  and 
Children  in  the  Faculty  of  Medicine  of  Paris.  Eighth  American,  from  the 
Eighth  French  and  First  Italian  Edition.  Edited  and  Enlarged  by  ROBERT 
J.  HESS,  M.D.,  Physician  to  the  Northern  Dispensary,  Phila.,  etc.,  with  an  Ap- 
pendix by  PAUL  F.  MUNDE,  M.D.,  Professor  of  Gynaecology  at  the  New  York 
Polyclinic,  and  at  Dartmouth  College;  Vice-President  American  Gynaecological 
Society,  etc.  Illustrated  by  Chromo-Lithographs,  Lithographs,  and  other  Full- 
page  Plates,  seven  of  which  are  beautifully  colored,  and  numerous  Wood  En- 
gravings. Students'.  Edition.  One  Vol.,  8vo.  Cloth,  $5.00;  Full  Leather,  $6.00 


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CHAVASSE.    The  Mental  Culture  and  Training  of  Children.         Cloth,  $1.00 
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and  Two  Colored  Lithographs.     8vo.  Cloth,  $3.50 

CLEVELAND'S  Pocket  Dictionary.  A  Pronouncing  Medical  Lexicon,  containing 
correct  Pronunciation  and  Definition  of  terms  used  in  medicine  and  the  col- 
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COHEN  on  Inhalation,  its  Therapeutics  and  Practice,  including  a  Description  of 

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COLLIE,  On  Fevers.  A  Practical  Treatise  on  Fevers,  Their  History,  Etiology, 
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COOPER  on  Syphilis  and  Pseudo-Syphilis.  By  ALFRED  COOPER,  F.R.C.S.,  Sur- 
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CROOKSHANK.  History  and  Pathology  of  Vaccination.  In  two  volumes. 
Vol.  I,  a  Critical  Inquiry.  Vol.  II  (Edited),  Selected  Essays.  By  EDGAR  M. 
CROOKSHANK,  M.B.,  Professor  of  Comparative  Pathology  and  Bacteriology  in 
King's  College,  London  ;  Author  of  a  "  Manual  of  Bacteriology,"  etc.  With  22 
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CROCKER.  Diseases  of  the  Skin.  Their  Description,  Pathology,  Diagnosis  and 
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Dis.  University  College  Hospital,  London.  With  Illustrations.  Cloth,  $5.50 

CULLINGWORTH.   A  Manual  of  Nursing,  Medical  and  Surgical.    By  CHARLES 

J.  CULLINGWORTH,   M.D.,   Physician  to  St.  Thomas'  Hospital,  London.     Third 

Revised  Edition.     With  18  Illustrations.     I2mo.  Cloth,  .75 

A  Manual  for  Monthly  Nurses.    Third  Edition.    321110.  Cloth,  .50 

DAVIS.  Biology.  An  Elementary  Treatise.  By  J.  R.  AINSWORTH  DAVIS,  of 
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DAY.     Diseases  of  Children.    A  Practical  and  Systematic  Treatise  for  Practitioners 

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On  Headaches.     The  Nature,  Causes  and  Treatment  of  Headaches.     Fourth 

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DERMATOLOGY,  Journal  of.  Edited  by  MALCOLM  MORRIS,  M.R.C.S.  London, 
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DORAN.  Gynaecological  Operations.  A  Handbook.  By  ALBAN  DORAN,  F.R.C.S., 
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166  Illustrations.  8vo.  Cloth,  $4.50 

DUCKWORTH.  On  Gout.  Illustrated.  A  treatise  on  Gout.  By  SIR  DYCE 
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MEDICAL  AND  SCIENTIFIC  PUBLICA  TIONS.  9 

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Third  Edition,  Enlarged,  with  new  Illustrations.  Cloth.  .75 

DTJRKEE,  On  Gonorrhoea  and  Syphilis.  By  SILAS  DURKEE,  M.D.  Sixth  Edition. 
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EDIS.  Sterility  in  Women.  By  A.  W.  EDIS,  M.D.,  F.R.C.P.,  late  President  British 
Gynaecological  Society;  Senior  Physician,  Chelsea  Hospital  for  Women;  Physician 
to  British  Lying-in  Hospital,  etc.  Illustrated.  8vo.  Cloth,  $1.75 

EDWARDS.    Bright's    Disease.     How  a  Person  Affected  with  Bright's  Disease 

Ought  to  Live.     By  Jos.  F.  EDWARDS,  M.D.     2d  Ed.     Reduced  to        Cloth,  .50 

Vaccination  and  Smallpox.    Showing  the  Reasons  in  favor  of  Vaccination, 

and  the  Fallacy  of  the  Arguments  advanced  against  it,  with  Hints  on  the 

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FAGGE.  The  Principles  and  Practice  of  Medicine.  By  C.  HILTON  FAGGE,  M.D., 
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and  Lecturer  on  Pathology  in,  Guy's  Hospital ;  Senior  Physician  to  Evelina  Hos- 
pital for  Sick  Children,  etc.  Arranged  for  the  press  by  PHILIP  H.  PYE-SMITH, 
1  M.D.,  Lect.  on  Medicine  in  Guy's  Hospital.  Including  a  section  on  Cutaneous 
Affections,  by  the  Editor;  Chapter  on  Cardiac  Diseases,  by  SAMUEL  WILKES,  M.D., 
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FIELD.  Evacuant  Medication — Cathartics  and  Emetics.  By  HENRY  M.  FIELD, 
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ber Gynaecological  Society  of  Boston,  etc.  I2mo.  288  pp.  Cloth,  $1.75 

FILLEBROWN.  A  Text-Book  of  Operative  Dentistry.  Written  by  invitation 
of  the  National  Association  of  Dental  Faculties.  By  THOMAS  FILLEBROWN,  M.D., 
D.M.D.,  Professor  of  Operative  Dentistry  in  the  Dental  School  of  Harvard  Uni- 
versity;  Member  of  the  American  Dental  Assoc.,  etc.  Illus.  Svo.  Clo.,  $2.50 

FLAGG.  Plastics  and  Plastic  Fillings,  as  pertaining  to  the  filling  of  all  Cavities 
of  Decay  in  Teeth  below  medium  in  structure,  and  to  difficult  and  inaccessible 
cavities  in  teeth  of  all  grades  of  structure.  By  J.  FOSTER  FLAGG,  D.D.S.,  Professor 
of  Dental  Pathology  in  Philadelphia  Dental  College.  Third  Revised  Edition. 
With  many  Illustrations.  Svo.  Cloth,  $4.00 

FLOWER'S  Diagrams  of  the  Nerves  of  the  Human  Body.  Exhibiting  their 
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of  the  Cutaneous  Surface  and  to  all  the  Muscles.  By  WILLIAM  H.  FLOWER, 
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POWER,  PH.D.  With  8  Lithographic  Plates.  Royal  octavo.  Cloth,  $1.50 

FOTHERGILL.  On  the  Heart  and  Its  Diseases.  With  Their  Treatment.  In- 
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Royal  College  of  Physicians  of  London.  2d  Ed.  Rewritten.  Svo.  Cloth,  $3. 50 

FOWLER'S  Dictionary  of  Practical  Medicine.  By  Various  Writers.  An  Ency- 
clopedia of  Medicine.  Edited  by  JAMES  KINGSTON  FOWLER,  M.A.,  M.D.,  F.R.C.P., 
Senior  Asst.  Physician  to,  and  Lecturer  on  Pathological  Anatomy  at,  the  Mid- 
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FOX   AND   GOULD.     Compend  on  Diseases  of  the   Eye  and  Refraction, 

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Assistant,  Ophthalmological  Department,  Jefferson  Medical  College  Hospital; 
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at  Moorfields,  London,  England,  etc.,  and  GEO.  M.  GOULD,  M.D.  Second  Edition. 
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Woman's  Medical  College;  Physician  in  charge  of,  and  Obstetrician  and 
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GOODHART  and  STARR'S  Diseases  of  Children.  The  Student's  Guide  to  the 
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the  University  of  Maryland.  Third  Edition.  Enlarged.  8vo.  Cloth,  $3.50 

GOULD'S  New  Medical  Dictionary.  Including  all  the  Words  and  Phrases  used 
in  Medicine,  with  their  proper  Pronunciation  and  Definitions,  based  on  Recent 
Medical  Literature.  By  GEORGE  M.  GOULD,  B.A.,  M.D.,  Ophthalmic  Surgeon  to 
the  Philadelphia  Hospital,  etc.,  With  Tables  of  the  Bacilli,  Micrococci,  Leuco- 
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MEDICAL  AND  SCIENTIFIC  PUBL1CA  TIONS.  11 

GOWERS,  Manual  of  Diseases  of  the  Nervous  System.  A  Complete  Text-book. 
By  WILLIAM  R.  GOWERS,  M.D.,  Prof.  Clinical  Medicine,  University  College, 
London.  Physician  to  National  Hospital  for  the  Paralyzed  and  Epileptic.  341 
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Diagnosis  of  Diseases  of  the  Brain.    8vo.    Second  Ed.    Illus.    Cloth,  $2.00 
Diagnosis  of  Diseases  of  the  Spinal  Cord.    4th  Edition.  Preparing. 

Medical  Ophthalmoscopy.  A  Manual  and  Atlas,  with  Colored  Autotype  and 
Lithographic  Plates  and  Wood-cuts,  comprising  Original  Illustrations  of  the 
changes  of  the  Eye  in  Diseases  of  the  Brain,  Kidney,  etc.  Third  Edition. 
Revised,  with  the  assistance  of  R.  MARCUS  GUNN,  F.R.C.S.,  Surgeon,  Royal 
London  Ophthalmic  Hospital,  Moorfields.  Octavo.  Cloth,  #5.50 

Syphilis  and  the  Nervous  System.  Being  the  Lettsomian  Lectures  for  1889. 
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GREENHOW.  Chronic  Bronchitis,  especially  as  connected  with  Gout,  Emphysema, 
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GROVES  AND  THORP.  Chemical  Technology.  A  new  and  Complete  Work. 
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Vol.  I.  FUEL.  By  Dr.  E.  J.  MILLS,  F.R.S.,  Professor  of  Chemistry,  Anderson 
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HABERSHON.  On  Some  Diseases  of  the  Liver.  By  S.  O.  HABERSHON,  M.D., 
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HADDON'S  Embryology.  An  Introduction  to  the  Study  of  Embryology.  For 
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of  Science,  Dublin.  190  Illustrations.  Cloth,  $6.00 

HALE.  On  the  Management  of  Children  in  Health  and  Disease.  A  Book  for 
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HARE.  Mediastinal  Disease.  The  Pathology,  Clinical  History  and  Diagnosis  of 
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tables  giving  the  Clinical  History  of  520  cases.  The  essay  to  which  was  awarded 
the  Fothergillian  Medal  of  the  Medical  Society  of  London,  1888.  By  H.  A. 
HARE,  M.D.  (Univ.  of  Pa.),  Demonstrator  of  Therapeutics  and  Instructor  in  Phy- 
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Biological  Department,  Univ  of  Pa.  8vo.  Illustrated  by  Six  Plates.  Cloth,  $2.00 

HARLAN.  Eyesight,  and  How  to  Care  for  It.  By  GEORGE  C.  HARLAN,  M.D., 
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HARLEY.  Diseases  of  the  Liver,  With  or  Without  Jaundice.  Diagnosis  and 
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Illustrations.  8vo.  Price  reduced.  Cloth,  $3.00  ;  Leather,  #4.00 

HARRIS.  On  the  Chest.  Including  the  Principal  Affections  of  the  Pleurae,  Lungs, 
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HARRIS'S  Principles  and  Practice  of  Dentistry.  Including  Anatomy,  Physi- 
ology, Pathology,  Therapeutics,  Dental  Surgery  and  Mechanism.  By  CHAPIN  A. 
HARRIS,  M.D.,  D.D.S.,  late  President  of  the  Baltimore  Dental  College,  author  of 
"  Dictionary  of  Medical  Terminology  and  Dental  Surgery."  Twelfth  Edition. 
Revised  and  Edited  by  FERDINAND  J.  S.  GORGAS,  A.M.,  M.D.,  D.D.S.,  author  of 
"Dental  Medicine;"  Professor  of  the  Principles  of  Dental  Science,  Dental 
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Medical  and  Dental  Dictionary.  A  Dictionary  of  Medical  Terminology, 
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HARTRIDGE,  Refraction.  The  Refraction  of  the  Eye.  A  Manual  for  Students. 
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HATFIELD.  Diseases  of  Children.  By  MARCUS  P.  HATFIELD,  Professor  of 
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No.  14,  f  Quiz- Compend ?  Scries.  I2mo.  Cloth,  $1.00 

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HEATH'S  Operative  Surgery.  A  Course  of  Operative  Surgery,  consisting  of  a 
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Text  of  Each  Operation.  By  CHRISTOPHER  HEATH,  F.R.C.S.,  Holme  Professor 
of  Clinical  Surgery  in  University  College,  London.  Quarto.  Second  Edition. 
Revised.  Sold  by  Subscription.  Cloth,  $12.00 

Minor  Surgery  and  Bandaging.  Ninth  Edition.  Revised  and  Enlarged. 
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Practical  Anatomy.  A  Manual  of  Dissections.  Seventh  London  Edition. 
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Injuries  and  Diseases  of  the  Jaws.  Third  Edition.  Revised,  with  over 
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HENRY.  Anaemia.  A  Practical  Treatise.  By  FRED'K  P.  HENRY,  M.D.,  Prof. 
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HIGGENS'  Ophthalmic  Practice.    A  Manual  for  Students  and  Practitioners.    By 

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Ophthalmic  Practice.    A  Handbook.    Second  Edition.    32mo.      Cloth,  .50 

HILL  AND  COOPER.    Venereal  Diseases.    The  Student's  Manual  of  Venereal 

Diseases,  being  a  concise  description  of  those  Affections  and  their  Treatment. 

SRKELEY  HILL,  M.D.,  Professor  of  Clinical  Surgery,  University  College,  and 

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MEDICAL  AND  SCIENTIFIC  PUBLICA  TfONS.  13 

HOLDEN'S  Anatomy.  A  Manual  of  the  Dissections  of  the  Human  Body.  By 
LUTHER  HOLDEN,  F.R.C.S.  Fifth  Edition.  Carefully  Revised  and  Enlarged. 
Specially  concerning  the  Anatomy  of  the  Nervous  System,  Organs  of  Special 
Sense,  etc.  By  JOHN  LANGTON,  F.R.C.S.,  Surgeon  to,  and  Lecturer  on  Anatomy 
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the  Author  and  Prof.  STEWART,  of  the  Royal  College  of  Surgeons'  Museum. 
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Landmarks.     Medical  and  Surgical.     4th  Edition.     Svo.  Cloth,  $1.25 

HOLLAND.  The  Urine,  the  Common  Poisons  and  the  Milk.  Memoranda,  Chem- 
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of  Medical  Chemistry  and  Toxicology  in  Jefferson  Medical  College,  of  Philadel- 
phia. Third  Edition.  Revised  and  Enlarged.  Illustrated  and  Interleaved. 
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HORWITZ'S  Compend  of  Surgery,  including  Minor  Surgery,  Amputations,  Frac- 
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Differential  Diagnosis  and  Treatment.  By  ORVILLE  HORWITZ,  B.S.,  M.D.,  Dem- 
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HUGHES.  Compend  of  the  Practice  of  Medicine.  Fourth  Edition.  Revised  and 
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16  P.  BLAKISTON,  SON  <S-  CO.'S 

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18  P.  BLAKISTONt  SON  &»  CO.'S  PUBLICA  TIONS. 

PHYSICIAN'S  VISITING  LIST.    Published  Annually.     Thirty-ninth  Year  of  its 
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ico        "          "  "           "                   "        ..        ..  u  200 


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t@T  This  List  combines  the  several  essential  qualities  of  strength,  compactness, 
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physicians.  It  is  not  an  elaborate,  complicated  system  of  keeping  accounts,  but  a 
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hence  its  popularity.  A  special  circular,  descriptive  of  contents  and  improvements, 
will  be  sent  upon  application. 

PEREIRA'S  Prescription  Book.  Containing  Lists  of  Terms,  Phrases,  Contrac- 
tions and  Abbreviations  used  in  Prescriptions,  Explanatory  Notes,  Grammatical 
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PIGGOTT  Copper  Mining  and  Copper  Ore.     I2mo.  Cloth,  $1.00 

PORTER'S  Surgeon's  Pocket-Book.  By  SURGEON-MAJOR  J.  H.  PORTER,  late  Pro- 
fessor of  Military  Surgery  in  the  Army  Medical  School,  Netley ,  England.  Revised, 
and  partly  Rewritten,  by  SURGEON-MAJOR  C.  H.  GODWIN,  of  the  Army  Medical 
School  (Netley,  England).  Third  Edition.  Small  I2mo.  Leather  Covers,  $2. 25 

POWER,  HOLMES,  ANSTIE  and  BARNES  (Drs.).  Reports  on  the  Progress  of 
Medicine,  Surgery,  Physiology,  Midwifery,  Diseases  of  Women  and  Children, 
Materia  Medica,  Medical  Jurisprudence,  Ophthalmology,  etc.  Reported  for  the 
New  Sydenham  Society.  8vo.  Paper,  .75  ;  Cloth,  $1.25 

POTTER.  A  Handbook  of  Materia  Medica,  Pharmacy  and  Therapeutics,  in- 
cluding the  Action  of  Medicines,  Special  Therapeutics,  Pharmacology,  etc.  In- 
cluding over  600  Prescriptions  and  Formulae.  By  SAMUEL  O.  L.  POTTER,  M.A., 
M.D.,  Professor  of  the  Practice  of  Medicine,  Cooper  Medical  College,  San  Fran- 
cisco ;  late  A.  A.  Surgeon  U.  S.  Army.  Second  Edition,  Revised  and  Enlarged. 
8vo.  With  Thumb  Index  tn  each  copy.  Cloth,  $4.00;  Leather,  $5.00 

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THE  PRACTICAL  SERIES 


THREE  NEW  VOLUMES. 


PARKES.  Hygiene  and  Public  Health.  A  Practical  Manual.  By  Louis  C. 
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Assistant  Professor  of  Hygiene  and  Public  Health,  at  University  College,  etc. 
I2mo.  Second  Edition.  Cloth,  $2.50 

LEWERS.  On  the  Diseases  of  Women.  A  Practical  Treatise.  By  Dr.  A.  H. 
N.  LEWERS,  Assistant  Obstetric  Physician  to  the  London  Hospital ;  and  Phy- 
sician to  Out-patients,  Queen  Charlotte's  Lying-in  Hospital;  Examiner  in  Mid- 
wifery and  Diseases  of  Women  to  the  Society  of  Apothecaries  of  London.  With 
146  Engravings.  Second  Edition,  Revised.  Cloth,  $2.50 

BTIXTOII.  On  Anaesthetics.  A  Manual  of  their  Uses  and  Administration.  By 
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of  Anaesthetics,  University  College  Hospital,  London.  Illustrated. 

Second  Edition  in  Press. 
COLLIE    On  Fevers.  A  Practical  Treat- 
ise on  Fevers,  Their  History,  Etiology. 
Diagnosis,  Prognosis  and  Treatment. 
By  ALEXANDER  COLLIE,  M.D.,  M.R.- 
C.P.,  Lond.    Medical  Officer  of  the  Ho- 
merton,  and  of  the  London  Fever  Hos- 
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RALFE.    Diseases  of  the  Kidney  and 

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REEVES.     Bodily    Deformities    and 

their  Treatment.  A  Handbook  of 
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MONEY.  On  Children.  Treatment  of 
Disease  in  Children,  including  the  Out- 
lines of  Diagnosis  and  the  Chief 
Pathological  Differences  between  Chil- 
dren and  Adults.  By  ANGEL  MONEY, 
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BARRETT.  Dental  Surgery  for  Gen- 
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HIGGENS,  Ophthalmic  Practice.  A 
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mic  Surgeon  to  Guy's  Hospital.  Illus- 
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*.£*  The  volumes  of  this  series,  written  by  well-known  physicians  and  surgeons  of  large 
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Bound  Uniformly,  in  a  Handsome  and  Distinctive  Cloth  Binding,  and 
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20  P.  BLAKISTON,  SON  6-  CO.'S 

POTTER.  Compend  of  Anatomy,  including  Visceral  Anatomy.  Formerly  pub- 
lished separately.  Based  upon  Gray.  Fifth  Edition.  Revised,  and  greatly 
Enlarged.  With  16  Lithographed  Plates  and  117  other  Illustrations.  Being- No. 
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Compend  of  Materia  Medica,  Therapeutics  and  Prescription  Writing, 
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Cloth,  $I.OQ.     Interleaved  for  taking  Notes,  $1.25 

PRITCHARD  on  the  Ear.  Handbook  of  Diseases  of  the  Ear.  By  URBAN 
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Aural  Surgeon  to  King's  College  Hospital,  Senior  Surgeon  to  the  Royal  Ear 
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PROCTER'S  Practical  Pharmacy.  Lectures  on  Practical  Pharmacy.  With  43 
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PROCTER.  Second  Edition.  Cloth,  $4.50 

RADCLIFFE  on  Epilepsy,  Pain,  Paralysis,  and  other  Disorders  of  the  Nervous 
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RALFE.    Diseases  of  the  Kidney  and  Urinary  Derangements.    By  C.  H.  RALFE. 

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REESE'S  Medical  Jurisprudence  and  Toxicology.  A  Text-book  for  Medical  and 

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REEVES.  Bodily  Deformities  and  their  Treatment.  A  Handbook  of  Practical 

Orthopaedics.  By  H.  A.  REEVES,  M.D.  Practical  Series.  See  Page  ig.  Cl.,$2.25 
RICHARDSON.  Long  Life,  and  How  to  Reach  It.  By  J.  G.  RICHARDSON,  Prof. 

of  Hygiene,  University  of  Penna.  Cloth,  .50 

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With  569  Illustrations.  8vo.  Cloth,  $4.50;  Leather,  $5.50 

RIGBY'S  Obstetric  Memoranda.    4th  Ed.    By  MEADOWS.    321110.         Cloth,  .50 

RICHTER'S  Inorganic  Chemistry.    A  Text-book  for  Students.    By  Prof.  VICTOR 

VON  RICHTER,   University  of  Breslau.      Third    American,  from  Fifth  German 

Edition.      Authorized  Translation  by  EDGAR  F.  SMITH,  M.A.,  PH.D.,  Prof,  of 

Chemistry,  University  of  Pennsylvania,  Member  of  the  Chemical  Societies  of 

Berlin  and  Paris.    89  Illustrations  and  a  Colored  Plate.     I2mo.          Cloth,  $2.00 

Organic  Chemistry.    A  Text-book  for  Students.    Translated  from  the  Fourth 

German  Ed.,  by  Prof.  Edgar  F.  Smith.     Illus.     Cloth,  $3.00  ;  Leather,  $3.50 

ROBERTS.  Bow-Legs.  Clinical  Lectures  on  Orthopaedic  Surgery.  By  A.  SYDNEY 
ROBERTS,  M.D.,  Instructor  in  Orthopaedic  Surg.  in  the  Univ.  of  Penn'a,  Surg.  to 
the  Univ.  Hospital.  Illustrated.  I2mo.  Cloth,  .50;  Boards,  .50 

ROBERTS.     Practice  of  Medicine.     The  Theory  and  Practice  of  Medicine.     By 

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London.    Eighth  Edition,  with  Illustrations.    8vo.      Cloth,  $5.50;  Leather,  $6.50 

Materia  Medica  and  Pharmacy.    A  Compend  for  Students.       Cloth,  #2.00 

ROBINSON.  Latin  Grammar  of  Pharmacy  and  Medicine.  By  H.  D.  ROBINSON, 
PH.D.,  Professor  of  Latin  Language  and  Literature,  University  of  Kansas,  Law- 
rence. With  an  Introduction  by  L.  E.  SAYRE,  PH.G.,  Professor  of  Pharmacy  in, 
and  Dean  of  the  Dept.  of  Pharmacy,  University  of  Kansas.  I2mo.  Cloth,  $2.00 

SANDERSON'S  Physiological  Laboratory.  A  Handbook  of  the  Physiological 
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and  T.  LAUDER  BRUNTON,  M.D.  With  over  350  Illustrations  and  Appropriate 
Letter-press  Explanations  and  References.  One  Volume.  Cloth,  $5.00 


MEDICAL  AND  SCIENTIFIC  PUBLICA  TIONS.  21 

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SCANZONI.  Sexual  Organs  of  Women.  A  Practical  Treatise  on  the  Diseases 
of  the  Sexual  Organs  of  Women.  By  F.  W.  VON  SCANZONI,  Prof,  of  Midwifery 
and  Diseases  of  Females,  University  of  Wurzburg,  etc.  Edited  by  A.  K.  GARD- 
NER, A.M.,  M.D.  60  Illustrations.  Fourth  Edition.  Octavo.  Cloth,  $4.00 

SCHNEE.  Diabetes,  its  Cause  and  Permanent  Cure.  From  the  standpoint  of  ex- 
perience and  Scientific  Investigation.  By  EMIL  SCHNEE,  Consulting  Physician 
at  Carlsbad.  Translated  from  the  German  by  R.  L.  TAFEL.  A.M.,  PH.D.  Re- 
vised and  Enlarged  by  the  author.  Octavo.  Cloth,  $2.oc 

SEWELL.  Dental  Surgery,  including  Special  Anatomy  and  Surgery.  By  HENRY 
SEWELL,  M.R.C.S.,  L.D.S.,  President  Odontological  Society  of  Great  Britain.  3d 
Edition,  greatly  enlarged,  with  about  200  Illustrations.  Cloth,  $3.00 

SMITH'S  Wasting  Diseases  of  Infants  and  Children.  By  EUSTACE  SMITH,  M.D., 
F.R.C.P.,  Physician  to  the  East  London  Children's  Hospital.  Fifth  London 
Edition,  Enlarged.  8vo.  Cloth,  $3.00 

Clinical  Studies  of  Diseases  in  Children.    Second  Edition.      Cloth,  $2.50 

SMITH.  Abdominal  Surgery.  Being  a  Systematic  Description  of  all  the  Princi- 
pal Operations.  By  J.  GREIG  SMITH,  M.A.,  F.R.S.E.,  Surg.  to  British  Royal  In- 
firmary. Illustrated.  Third  Edition.  Cloth,  $7.00 

SMITH.  Electro-Chemical  Analysis.  By  EDGAR  F.  SMITH,  Prof,  of  Analytical 
Chemistry,  University  of  Penna.  26  Illustrations.  I2mo.  Cloth,  $1.00 

SMITH  (TYLER).  Lectures  on  Obstetrics.  Delivered  at  St.  Mary's  Hospital. 
With  an  Introductory  Lecture  on  the  History  and  Art  of  Midwifery,  and  Copious 
Annotations.  By  A.  K.  GARDNER,  A.M.,  M.D.  233  Illus.  3d  Ed.  8vo.  Cloth,  $4.00 

STAMMER.  Chemical  Problems,  with  Explanations  and  Answers.  By  KARL 
STAMMER.  Translated  from  the  2d  German  Edition,  by  Prof.  W.  S.  HOSKINSON, 
A.M.,  Wittenberg  College,  Springfield,  Ohio.  I2mo.  Cloth.  .75 

STARR  and  WALKER.  Physiological  Action  of  Medicines.  Prepared  for  the 
use  of  Students  of  the  Medical  Department,  University  of  Penna.  By  Louis 
STARR,  M.D.,  J.  B.  WALKER,  M.D.  and  W.  M.  POWELL,  M.D.  Third  Edition. 
Enlarged.  32mo.  Cloth,  .75 

STARR.  The  Digestive  Organs  in  Childhood.  Second  Edition.  The  Diseases 
of  the  Digestive  Organs  in  Infancy  and  Childhood.  With  Chapters  on  the 
Investigation  of  Disease  and  the  Management  of  Children.  By  Louis  STARR, 
M.D.,  late  Clinical  Prof,  of  Diseases  of  Children  in  the  Hospital  of  the  University 
of  Penn'a;  Physician  to  the  Children's  Hospital,  Phila.  Second  Edition. 
Revised.  In  many  parts  rewritten.  Illustrated  by  two  Lithograph  Plates  and 
numerous  wood-engravings.  Crown  Octavo.  Cloth,  $2.50 

The  Hygiene  of  the  Nursery,  including  the  General  Regimen  and  Feed- 
ing of  Infants  and  Children,  and  the  Domestic  Management  of  the  Ordinary 
Emergencies  of  Early  Life.  Second  Edition.  Enlarged.  24  Illustrations. 
I2mo.  280  pages,  Cloth,  $1.00 

See  also  Goodhart  and  Starr.    Page  10. 

STEWART'S  Compend  of  Pharmacy.  Based  upon  "  Remington's  Text-Book  of 
Pharmacy."  By  F.  E.  STEWART,  M  D.,  PH.G.,  Quiz  Master  in  Chem.  and  Theoreti- 
cal Pharmacy,  Phila.  College  of  Pharmacy  ;  Demonstrator  and  Lect.  in  Pharma- 
cology, Medico-Chirurgical  College,  and  in  Woman's  Medical  College.  3d.  Ed. 
With  complete"  tables  of  Metric  and  English  Systems  of  Weights  and  Measures 
and  an  elaborate  Index.  ? Quiz- Compend?  Series.  Cloth,  $1.00 

Interleaved  for  the  addition  of  notes,  $1.25 


22  »          P.  SLAKISTON,  SON  &-  CO.'S 

STIRLING.  Outlines  of  Practical  Physiology.  Including  Chemical  and  Experi- 
mental Physiology,  with  Special  Reference  to  Practical  Medicine.  By  W.  STIR- 
LING, M.D.,  SC.D.,  Prof,  of  Phys.,  Owens  College,  Victoria  University,  Manchester. 
Examiner  in  Honors  School  of  Science,  Oxford,  England.  142  Illustrations. 
309  pages.  Cloth,  $2.25 

Outlines  of  Practical  Histology.  A  Manual  for  Students.  With  344  Illus- 
trations. 121110.  Cloth,  $4.co 

STOCKEN'S  Dental  Materia  Medica.  Dental  Materia  Medica  and  Therapeutics, 
with  Pharmacopoeia.  By  JAMES  STOCKEN,  D.D.S.  Third  Edition.  Cloth,  $2.50 

STRAHAN.  Extra-Uterine  Pregnancy.  The  Diagnosis  and  Treatment  of  Extra- 
Uterine  Pregnancy.  Being  the  Jenks  Prize  Essay  of  the  College  of  Physicians 
of  Philadelphia.  By  JOHN  STRAHAN,  M.D.  (Univ.  of  Ireland),  late  Res.  Surgeon 
Belfast  Union  Infirmary  and  Fever  Hospital.  Octavo.  Cloth,  $1.50 

BUTTON'S  Volumetric  Analysis.  A  Systematic  Handbook  for  the  Quantitative 
Estimation  of  Chemical  Substances  by  Measure,  Applied  to  Liquids,  Solids  and 
Gases.  By  FRANCIS  SUTTON,  F.C.S.  Sixth  Edition,  Revised  and  Enlarged, 
with  Illustrations.  8vo.  Cloth,  $5.co 

SUTTON.  Ligaments.  Their  Nature  and  Morphology.  By  JOHN  BLAND  SUTTON, 
F.R.C.S.,  Lecturer  on  Pathology,  Royal  College  of  Surgeons ;  Assis.  Surg.  and 
Dem.  of  Anatomy,  Middlesex  Hospital,  London.  Illustrated.  I2mo.  Clo'th,  $1.25 

SWAIN.  Surgical  Emergencies,  together  with  the  Emergencies  Attendant  on 
Parturition  and  the  Treatment  of  Poisoning.  A  Manual  for  the  Use  of  General 
Practitioners.  By  W.  F.  SWAIN,  F.R.C.S.  Fourth  Edition.  Illustrated.  $1.50 

SWANZY.  Diseases  of  the  Eye  and  their  Treatment.  A  Handbook  for  Physi- 
cians and  Students.  By  HENRY  R.  SWANZY,  A.M.,  M.B.,  F.R.C.S. i.,  Surgeon  to 
the  National  Eye  and  Ear  Infirmary  ;  Ophthalmic  Surgeon  to  the  Adelaide  Hos- 
pital, Dublin ;  Examiner  in  Ophthalmic  Surgery  in  the  Royal  University  of 
Ireland.  Third  Edition.  Thoroughly  Revised.  158  Illustrations.  508  pages. 
I2mo.  Cloth,  $3.00 

SWAYNE'S  Obstetric  Aphorisms,  for  the  Use  of  Students  commencing  Midwifery 
Practice.  By  JOSEPH  G.  SWA YNE,  M.D.  Ninth  Edition.  Illus.  Cloth,  $1.25 

SYMONDS  Manual  of  Chemistry,  for  the  special  use  of  Medical  Students.  By 
BRANDRETH  SYMONDS,  A.M.,  M.D.,  Asst.  Physician  Roosevelt  Hospital,  Out- 
Patient  Department ;  Attending  Physician  Northwestern  Dispensary,  New  York. 
I2mo.  Cloth,  $2.00;  Interleaved  for  Notes,  $2.40 

TAFT'S  Operative  Dentistry.     A  Practical  Treatise  on  Operative  Dentistry.     By 
JONATHAN  TAFT,  D.D.S.     Fourth  Revised  and  Enlarged  Edition.     Over  100  Il- 
lustrations.    8vo.  Cloth,  $4.25  ;  Leather,  $5.00 
Index  of  Dental  Periodical  Literature     8vo.  Cloth,  $2.00 

TALBOT.  Irregularities  of  the  Teeth,  and  Their  Treatment.  By  EUGENE  S. 
TALBOT,  M.D.,  Professor  of  Dental  Surgery  Woman's  Medical  College,  and 
Lecturer  on  Dental  Pathology  in  Rush  Medical  College,  Chicago.  Second  Edi- 
tion, Revised  and  Enlarged  by  about  100  pages.  Octavo.  234  Illustrations. 
(169  of  which  are  original).  261  pages.  Cloth,  13.00 

TANNER'S  Index  of  Diseases  and  their  Treatment.  By  THOS.  HAWKES  TANNER, 
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M.D.  With  Additions.  Appendix  of  Formulae,  etc.  8vo.  Cloth,  $3.00 

Memoranda  of  Poisons  and  their  Antidotes  and  Tests.  Sixth  American,  from 
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of  Chemistry  in  Pennsylvania  College  of  Dental  Surgery  and  in  the  Phila- 
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HENRY  THOMPSON,  F.R.C.S.,  Emeritus  Professor  of  Clinical  Surgery  in  Univer- 
sity College.     Third  Edition.    With  87  Engravings.     8vo.  Cloth,  $3.50 
Urinary  Organs,    Diseases  of  the  Urinary  Organs.    Containing  32  Lectures. 
Eighth  London  Ed.    Octavo.     470  pages.  Cloth,  $3.50 

On  the  Prostate.     Diseases  of  the  Prostate.     Their  Pathology  and  Treatment. 

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THORBURN.  Surgery  of  the  Spinal  Cord.  A  Contribution  to  the  study  of.  By 
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TOMES'  Dental  Anatomy.  A  Manual  of  Dental  Anatomy,  Human  and  Compara- 
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24  P.  BLAKISTON,  SON  6-  CO.'S 

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Anatomy  in  the  University  of  Pennsylvania.     Including  a  Section  on  Retinitis  in 

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WALSH  AM.    Manual  of  Practical  Surgery.    For  Students  and  Physicians.    By 

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WARREN.    Compend  Dental  Pathology  and  Dental  Medicine.    Containing  all 

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WARREN,  D.D.S.,  Clinical  Chief,  Penn'a  College  of  Dental  Surgery,  Phila.  Illus. 
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By  C.  J.  B.  WILLIAMS,  M.D.  Second  Edition.  Enlarged  and  Rewritten.  By  C. 
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WILSON.    The  Summer  and  Its  Diseases.    By  JAMES  C.  WILSON,  M.D.    Cloth,  .50 

WINCKEL.  Diseases  of  Women.  Second  Edition.  .  Including  the  Dis- 
eases of  the  Bladder  and  Urethra.  By  Dr.  F.  WINCKEL,  Professor  of 
Gynaecology,  and  Director  of  the  Royal  University  Clinic  for  Women,  in  Munich. 
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Text-Book  of  Obstetrics ;  Including  the  Pathology  and  Therapeutics  of  the 
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WOAKES.    Post-Nasal  Catarrh  and  Diseases  of  the  Nose,  causing  Deafness.    By 

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WOLFF.  Manual  of  Applied  Medical  Chemistry  for  Students  and  Practitioners  of 
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WOOD.  Brain  Work  and  Overwork.  By  Prof.  H.  C.  WOOD,  Clinical  Professor 
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WOODY.  Essentials  of  Chemistry  and  Urinalysis.  By  SAM  E.  WOODY,  A.M.; 
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WYNTER  and  WETHERED.  Clinical  and  Practical  Pathology.  A  Manual 
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istrar and  late  Dem.  of  Anat.  and  Chem.  at  the  Middlesex  Hospital,  and 
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Dose  and  Symptom  Book.    The  Physician's  Pocket  Dose  and  Symptom  Book. 
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|  WALSHAM,  M  D.,  Asst.  Surgeon  to,  and  Demonstrator  of  Surgery  in,  St.  Bartholomew's  Hospital;  Sur- 
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m  the  Polycl'nic.  * 

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i  by  THEOPHILUS  PARVIN,  M.D.,  Professor  of  Obstetrics  and  Diseases  of  Women  and  Children  in  Jeffer- 
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GERALD  F.  YEO,  M.D.,  F.R.C.S.,  Professor  of  Physiology  in  King's  College,  London-.  321  Illustra- 
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iHTER'S  ORGANIC  CHEMISTRY.  By  PROF.  VICTOR  VON  RICHTER,  University  of  Breslau. 
Authorized  translation.  Pirst  American,  from  the  Fourth  German  Edition.  By  EDGAR  F.  SMITH,  M.D., 
PH  D  ,  Translator  of  Richter's  Inorganic  Chemistry ;  Prof,  of  Chemistry  in  Wittenberg  College,  Spring- 
field, Ohio;  formerly  in  the  Laboratories  of  the  University  of  Pennsylvania;  Member  of  the  Chemical 
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3DHARTAND  STARR,  DISEASES  OF  CHILDREN.  Second  Edition.  By  J.  F.GOODHART, 
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Second  American  from  third  English  Edition.  Revised  and  Edited  by  Louis  STARR,  M.D.,  Clinical 
Professor  of  Diseases  of  Children  in  the  Hospital  of  the  University  of  Pennsylvania,  and  Physician  to  the 
Children's  Hospital,  1  hila.  With  many  new  Prescriptions  and  Directions  for  making  Artificial  Human 
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i  The  New  York  Medical  Record. 

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rlieve,  a  mission,  particularly  in  the  hands  of  the  young  members  of  the  profession.     In  these  days  oi  prolixity  in  medical 
lure,  it  is  refreshing  to  meet  with  an  author  who  knows  both  what  to  say  and  when  he  has  said  it." 
.RING'S   PRACTICAL  THERAPEUTICS.     Fourth  Edition.     A  Manual  of  Practical  Thera- 
peutics,   considered  with  reference  to  Articles  of  the  Materia  Medica.     Containing,  also,  an  Index  of 
I  Diseases,  with   a  list  of   Medicines  applicable  as   Remedies,  and   a  full  Index  of  the  Medicines  and 
;  Preparations   noticed  in   the   work.      By   EDWARD  JOHN   WARING,   M.D.,   F.R.C.P.,   F.L.S.,   etc.     4th 
Edition.     Rewritten  and  Revised.    Edited  by  DUDLEY  W.  BUXTON.  M.D  ,  Asst.  to  the  Prof,  of  Medicine 
at  University  College  Hospital;  Member  of  the  Royal  College  of  Physicians  of  London.     666  pages. 

Cloth,  $3.00;  Leather,  $3.50 
t  The  Kansas  City  Medical  Record. 

As  a  work  of  reference  it  excels,  on  account  of  the  several  complete  indexes  added  to  this  edition.  It  was  deservedly 
I  ,ar  in  former  editions,  and  will  be  more  so  in  the  one  before  us,  on  account  of  the  careful  arrangement  of  the  subjects." 

£SE'S  MEDICAL  JURISPRUDENCE  AND  TOXICOLOGY.  Second  Edition.  By  JOHN  T. 
REESK,  M.D.,  Professor  of  Medical  Jurisprudence  and  Toxicology  in  the  University  of  Pennsylvania  ;  late 
President  of  the  Medical  Jurisprudence  Society  of  Philadelphia;  Physician  to  St.  Joseph's  Hospital; 
Member  of  the  College  of  Physicians  of  Phila.;  Corresponding  Membtr  of  the  New  York  Medico- Legal 
Society,  etc.  2d  Edition.  Revised  and  Enlarged.  654  pages.  Cloth,  $3  oo;  Leather,  #3.50 

THE   MOST   PRACTICAL  SERIES  OF  TEXT-BOOKS. 


JUST  PUBLISHED.     THIRD  EDITION. 

HUMAN  PHYSIOLOG1 

BY  LANDOIS  AND  STIRLING. 

With  692  Illustrations. 

THIRD    AMERICAN,   FROM    THE    SIXTH    GERMAN    EDITION. 

A  Text-Book  of  Human  Physiology,  including  Histology  and  Microscopical  Anatc 
•with  special  reference  to  the  requirements  of  Practical  Medicine. 
Dr.  L.  LANDOIS,  Professor  of  Physiology  and  Director  of  the  Physiological  Instil 
University  of  Greifswald.     Translated  from  the  Fifth  German  Edition,  with  a 
tions   by  WM.  STIRLING,  M.D.,  SC.D.,  Brackenbury,  Professor  of    Physiology 
Histology  in  Owen's  College  and  Victoria  University,  Manchester;    Examine 
the  Honors'  School  of  Science,  University  of  Oxford,  England.      Third  Editi 
revised  and  enlarged.     692  Illustrations. 
"A   BRIDGE    BETWEEN    PHYSIOLOGY   AND    PRACTICAL    MEDICINE." 

One  Volume.    Royal  Octavo.    Cloth,  $6.50 ;  Leather,  $7.50. 

From  the  Prefaces  to  the  English  Edition. 

The  fact  that  Prof.  Landois'  book  has  passed  through  four  large  editions  in  the  original  since  1880 
that  in  barely  six  months'  time  a  second  edition  of  the  English  has  been  called  for,  shows  that  in  i 
special  way  it  has  met  a  want.  The  characteristic  which  has  thus  commended  the  work  will  be  f 
mainly  to  lie  in  its  eminent  practicability;  and  it  is  ihis  consideration  which  has  induced  me  to  undertake 
task  of  putting  it  into  English.  Landois'  work,  in  fact,  forms  a  Bridge  between  Physiology  and  the  Pra 
of  Medicine.  It  never  loses  sight  of  the  fact  that  -the  student  of  to-day  is  the  practicing  physicia 
to-morrow.  In  the  same  way,  the  work  offers  to  the  busy  physician  in  practice  a  ready  means  of  refres 
his  memory  on  the  theoretical  aspects  of  Medicine.  He  can  pass  backward  from  the  examination  of  pi 
logical  phenomena  to  the  normal  processes,  and,  in  the  study  of  these,  find  new  indications  and  new  1 
for  the  appreciation  and  treatment  of  the  cases  under  consideration.  With  this  object  in  view,  all 
methods  of  investigation  which  may,  to  advantage,  be  used  by  the  practitioner,  are  carefully  and 
described.  Many  additions,  and  about  one  hundred  illustrations,  have  been  introduced  into  this  sei 
English  edition,  and  the  whole  work  carefully  revised. 

PRESS  NOTICES. 

"  Most  effectively  aids  the  busy  physician  to  trace  from  morbid  phenomena  back  the  course  of  divergence 
healthy  physical  operations,  and  to  gather  in  this  way  new  lights  and  novel  indications  for  the  COMPREHENSION  AND  TREAT: 
ot  the  maladies  with  which  he  is  called  up  in  to  cope." — American  Journal  of  Medical  Sciences. 

"  I  know  of  no  book  which  is  its  equal  in  the  applications  to  the  needs  of  clinical  medicine." — Prof.  Harrison  Allen 
Professor  of  I  hysiology,  University  of  Pennsylvania. 

"  We  have  no  hesitation  in  saying  that  THIS  is  THE  WORK  to  which  the  PRACTITIONER  will  turn  whenever  he  desires 
thrown  upon  the  phenomena  of  a  COMPLICATED  OR  IMPORTANT  CASE." — Edinburgh  Medical  Journal. 

"  So  great  are  the  advantages  offered  by  Prof.  LANDOIS'  TEXT-BOOK,  from  the  EXHAUSTIVE  and  EMINENTLY  PRACI 
manner  in  which  the  subject  is  treated,  that  it  has  passed  through  FOUR  large  editions  in  the  same  number  of  years.) 
Dr.  STiRLiNG's'annotations  have  materially  added  to  the  value  of  the  work.  Admirably  adapted  for  the  PRACTITIONER. 
With  this  Text-book  at  command,  NO  STUDENT  COULD  FAIL  IN  HIS  EXAMINATION." — The  Lancet. 

"One  of  the  MOST  PRACTICAL  WORKS  on  Physiology  ever  written,  forming  a  '  bridge  '  between  Physiology  and  Prai 
Medicine.  .  .  .  Its  chief  merits  are  its  completeness  and  conciseness.  .  .  .  The  additions  by  the  Editor  are  able  and  judi^ 
.  .  .  EXCELLENTLY  CLKAR,  ATTRACTIVE  and  SUCCINCT." — British  Medical  Journal. 

"  The  great  subjects  dealt  with  are  treated  in  an  admirably  clear,  terse,  and  happily  illustrated  manner." — Practition^ 

"  Unquestionably  the  most  admirable  exposition  of  the  relations  of  Human  Physiology  to  Practical  Medicine  eve;! 
before  English  readers  " — Stuaents'  Journal. 

"  As  a  work  of  reference,  LANDOIS  and  STIRLING'S  Treatise  OUGHT  TO  TAKE  THB  FOREMOST  PLACE  among  thej 
books  in  the  English  language.  The  wood-cuts  are  noticeable  for  their  number  and  beauty." — Glasgoiv  Medical  Journal. 

"  Landois'  Physiology  is,  without  question,  the  best  text-book  on  the  subject  that  has  ever  been  writ! 
— New  York  Medical  Record. 

"  The  chapter  on  the  Brain  and  Spinal  Cord  will  be  a  rrost  valuable  one  for  the  general  reader,  the  translator's  notes  ajj 
not  a  little  to  its  importance.  The  sections  on  Sight  and  Hearing  are  exhaustive.  .  .  .  The  Chemistry  of  the  Urine  is  thoroi' 
considered.  ...  In  its  present  form,  the  value  of  the  original  has  been  greatly  increased.  .  .  .  The  text  is  smooth,  acci 
and  unusually  fiee  from  Germanisms  ;  in  fact,  it  is  good  English." — New  York  Medical  Journal. 

"  It  is  not  for  the  physiological  student  alone  that  Prof.  Landois'  book  possesses  great  value,  for  IT  HAS  BEEN  ADDRI 
TO  THE  PRACTITIONER  OF  MEDICINE  as  well,  who  will  find  here  a  direct  application  of  physiological  to  pathological  proces 
Medical  Bulletin. 

P.  BLAKISTON,  SON  &  CO.,  Publishers,  1012  Walnut  St.,  Philadelpl 


DISEASES  OF  THE  SKIN. 

BY  T.  MCCALL  ANDERSON,  M.  D., 

Professor  of  Clinical  Medicine  in  the   University  of  Glasgow, 

ASSISTED  BY 

s  DR.  JAMES  CHRISTIE,  Sec'y  London  Epidemiological  Society  for  Indian  Ocean  and  East  Africa;  Mem. 
Jical  Soc.  of  Bombay,  etc.  DR.  HECTOR  C.  CAMERON,  Surgeon  and  Lecturer  to  Western  Infirmary, 
^gow;  Surgeon  to  Glasgow  Hospital  for  Children,  etc.  WILLIAM  MACEWEN,  M.B.,  M.D.,  Lecturer  on 

ematic  and  Clinical  Sargery,  Royal  Infirmary;  Surgeon  to  Royal  Infirmary  and  Children's  Hospital, 

;gow,  etc. 

.WITH  COLORED  PLATES  AND  NUMEROUS  WOOD  ENGRAVINGS. 

fi  Octavo.     650  Pages.     Cloth,  $4.50  ;  Leather,  $5.50. 

^ 

£  treatise  on  Diseases  of  the  Skin,  with  reference  to  Diagnosis  and  Treatment, 

luding  an  Analysis  of  11,000  Consecutive  Cases.  Thoroughly  illustrated  by  new  and 
•dsome  wood  engravings,  and  several  colored  and  steel  plates  prepared,  under  the 
Action  of  the  author,  from  special  drawings  by  Dr.  John  Wilson. 

t      PARTICULARLY  STRONG  IN  TREATMENT. 

fesr*  Special  attention  is  given  to  the  Differential  Diagnosis  of  Skin  Diseases  and  to  the 
itment.  There  are  over  150  prescriptions,  which  will  serve  as  hints  to  the  physician 

"lealing  with  obstinate  and  chronic  cases. 

^here  has  been  no  complete  treatise  on  Dermatology  issued  for  several  years  ;  Professor 

person  has,  therefore,  chosen  an  opportune  time  to  publish  his  book. 

t 
',] 


ILLUSTRATING  ONE  OF  THE  DISEASES  OF  THE  HAIK  (See  Fig.  b,pdge  7). 

;or  nearly  twenty-five  years  Professor  Anderson  has  been  a  general  practitioner  and  a 
Epital  physician,  with  unusual  opportunities  for  the  study  of  this  class  of  diseases,  though 
c  a  "specialist,"  as  the  term  is  understood.  His  experience  is,  therefore,  of  great 
Je,  and  the  physician  will  feel  that,  in  consulting  this  work,  he  is  reading  the  expe- 
}ces  of  a  man  situated  as  himself — with  the  same  difficulties  of  diagnosis  and  treatment, 
f.  who  has  surmounted  them  successfully.  We  believe  this  to  be  a  valuable  feature  of 
;',book  that  will  be  recognized  at  once;  for  it  is  undoubtedly  a  fact  that  a  work  like 

present  contains  much  practical  information  and  many  hints  not  to  be  found  else- 
|re.  Professor  Anderson  is  particularly  happy  in  illustrating  the  impor- 
lt  relations  subsisting  between  the  general  economy  and  its  covering,  and 
,  ideas  of  pathology  and  therapeutics,  including  a  consideration  of  all  the  general 

local  manifestations  of  the  common  diseases  of  the  economy  which  are  manifested 

n  the  surface,  will  find  many  appreciative  readers. 
Diseases  of  the  hair  receive  full  systematic  treatment. 

]  We  welcome  Dr.  Anderson's  work  not  only  as  a  friend,  but  as  a  benefactor  to  the  profession,  because  the  author  has 
-ien  off  mediaeval  shackles  of  insuperable  nomenclature  and  made  crooked  ways  straight  in  the  diagnosis  and  treatment  of 
,itherto  but  little  understood  class  of  diseases.  The  chapter  on  Eczema  is,  alone,  worth  the  price  of  the  book."— Nashville 
\ul  .\e-ws. 


NEW  AND 
REVISED 
EDITIONS. 


PQU1Z-COMPENDS.? 


A  SERIES  OF  PRACTICAL  MANUALS  FOR  THE  PHYSICIAN  AND  STUDENT. 

Compiled  in  accordance  with  the  latest  teachings  of  prominent  lecturers 
and  the  most  popular  Text-books. 

Bound  in  Cloth,  each  $1.00.     Interleaved,  for  the  Addition  of  Notes,  $1.25. 
They  form  a  most  complete,  practical  and  exhaustive  set  of  manuals,  containing  information 
nowhere  else  collected  in  such  a  practical  shape.     Thoroughly  up  to  the  times  in  every  respect, 
containing  many  new  prescriptions  and  formulae,  an4  over  300  illustrations,  many  of  which  have 
been  drawn  and  engraved  specially  for  this  series.     The  authors  have  had  large  experience  as 
quiz-masters  and  attaches  of  colleges,  with  exceptional  opportunities  for  noting  the  most  recent 
advances  and  methods.     The  arrangement  of  the  subjects,  illustrations,  types,  etc.,  are  all  of  the 
most  approved  form.     They  are  constantly  being  revised,  so  as  to  include  the  latest  and  best 
teachings,  and  can  be  used  by  students  of  any  college  of  medicine,  dentistry  and  pharmacy. 
No.   i.     Human    Anatomy.      Fifth    Edition,  including    Visceral   Anatomy,  formerly 
published  separately.      16  Lithograph  Plates,  Tables,  and  117  Illustrations.     By 
SAMUEL  O.  L.  POTTER  M.A.,  M.D.,  late  A.  A.  Surgeon,  U.  S.  Army.    Professor  of  Practice, 
Cooper  Med.  College,  San  Francisco. 

Nos.  2  and  3.  Practice  of  Medicine.  Fourth  Edition,  Enlarged.  By  DANIEL  E. 
HUGHES,  M.D.,  late  Demonstrator  of  Clinical  Medicine  in  Jefferson  Med.  College,  Phila. ; 
Physician-in  Chief,  Philadelphia  Hospital.  In  two  parts. 

PART  I. — Continued,  Eruptive  and  Periodical  Fevers,  Diseases  of  the  Stomach,  Intestines,  Peritoneum, 
Biliary  Passages,  Liver,  Kidneys,  etc.  (including  Tests  for  Urine),  General  Diseases,  etc. 

PART  II.  — Diseases  of  the  Respiratory  System  (including  Physical  Diagnosis),  Circulatory  System  and 
Nervous  System  ;  Diseases  of  the  Blood,  etc. 

***  These  little  books  can  be  regarded  as  a  lull  set  of  notes  upon  the  Practice  of  Medicine,  containing  the 
Synonyms,  Definitions,  Causes,  Symptoms,  Prognosis,  Diagnosis,  Treatment,  etc.,  of  each  disease,  and  including 
a  number  of  prescriptions  hitherto  unpublished. 

No.  4.  Physiology,  including  Embryology.  Fifth  Edition.  By  ALBERT  P.  BRUBAKER, 
M.D.,  Prof,  of  Physiology,  Penn'a  College  of  Dental  Surgery ;  Demonstrator  of  Physiology 
in  Jefferson  Med.  College,  Phila.  Revised,  Enlarged  and  Illustrated. 

No.  5.  Obstetrics.  Illustrated.  Fourth  Edition.  For  Physicians  and  Students.  By 
HENRY  G.  LANDIS,  M.D.,  Prof,  of  Obstetrics  and  Diseases  of  Women,  in  Starling  Medical 
College,  Columbus.  Revised  Edition.  New  Illustrations. 

No.  6.  Materia  Medica,  Therapeutics  and  Prescription  Writing.  Fifth  Revised 
Edition.  With  especial  Reference  to  the  Physiological  Action  of  Dru^s,  and  a  complete 
article  on  Prescription  Writing.  Based  on  the  Last  Revision  (Sixth)  of  the  U.  S.  Pharma- 
copoeia, and  including  many  unofficinal  remedies.  By  SAMUEL  O.  L.  POTTER,  M.A.,  M.D., 
late  A.  A.  Surg.  U.  S.  Army ;  Prof,  of  Practice,  Cooper  Med.  College,  San  Francisco.  5th 
Edition.  Improved  and  Enlarged. 

No".  7.  Gynaecology.  A  Compend  of  Diseases  of  Women.  By  HENRY  MORRIS,  M.D., 
Demonstrator  of  Obstetrics,  Jefferson  Medical  College,  Philadelphia.  Many  Illustrations. 

No.  8.  Diseases  of  the  Eye  and  Refraction,  including  Treatment  and  Surgery.  By  L. 
WEBSTER  Fox,  M.D.,  Chief  Clinical  Assistant  Opthalmological  Dept.,  Jefferson  Medical 
College,  etc.,  and  GEO.  M.  GOULD,  A.B.  71  Illustrations,  39  Formulae.  2d  Edition. 

No.  9.  Surgery,  Minor  Surgery  and  Bandaging.  Illustrated.  Fourth  Edition.  Includ- 
ing Fractures,  Wounds,  Dislocations,  Sprains,  Amputations  and  other  operations;  Inflam- 
mation, Suppuration,  Ulcers,  Syphilis,  Tumors,  Shock,  etc.  Diseases  of  the  Spine,  Ear, 
Bladder,  Testcles,  Anus,  and  other  Surgical  Diseases.  By  ORVILLE  HORWITZ,  A.M.,  M.D., 
Demonstrator  of  Surgery,  Jefferson  Medical  College.  84  Formulae  and  136  Illustrations. 

No.  10.  Medical  Chemistry.  Third  Edition.  Inorganic  and  Organic,  including  Urine 
Analysis.  For  Medical  and  Dental  Students.  By  HENRY  LF.FFMANN,  M.D.,  Prof,  of  Chem- 
istry in  Penn'a  College  of  Dental  Surgery,  Phila.  Third  Edition.  Revised  and  Enlarged. 

No.  ii.  Pharmacy.  Based  upon  "Remington's  Text-Book  of  Pharmacy."  By  F.  E. 
STEWART,  M.D.,  PI'I.G.,  Professor  of  Pharmacy,  Powers  College  of  Pharmacy;  late  Quiz- 
Master  at  Philadelphia  College  of  Pharmacy.  Third  Edition.  Revised. 

No.  12.  Veterinary  Anatomy  and  Physiology.  Illustrated.  By  WM.  R.  BALLOU,  M.D., 
Prof,  of  Equine  Anatomy,  New  York  College  of  Veterinary  Surgeons,  etc.  29  Illustrations. 

No.  13.  Dental  Pathology  and  Dental  Medicine.  Containing  all  the  most  noteworthy 
points  of  interest  to  the  Dental  student.  By  GEO.  W.  WARREN,  D.D.S.,  Clinical  Chief, 
Penn'a  College  of  Dental  Surgery,  Philadelphia.  Illus. 

No.  14.  Diseases  of  Children.  By  MARCUS  P.  HATFIELD,  Professor  of  Diseases  of 
Children,  Chicago  Medical  College.  With  Colored  Plate. 

These  books  are  constantly  revised  to  keep  up  'with  the  latest  teachings  and  discoveries. 


"IT  STANDS  WITHOUT  AN  EQUAL  AS  THE  MOST  COMPLETE  WORK  ON  PRACTICE  IN 
THE  ENGLISH  LANGUAGE."— New  York  Medical  Journal. 

FAGGE'S  PRACTICE  OF  MEDICINE,  . 

Two  Large  Royal  Octavo  Volumes.     Containing  over  1900  Pages. 
PRICE,  HANDSOMELY   BOUND  IN  CLOTH,  S8.OO. 

The  Principles  and  Practice  of  Medicine. 

Bv  CHARLES  HILTON  FAGGE,  M.D.,  F.R.C.P.,  F.R.M.C.S., 

Examiner  in  Medicine,  University  of  London  ;  Physician  to,  and  Lecturer  on  Pathology  in,  Guy's  Hospital; 
Senior  Physician  to  Evelina  Hospital  for  Sick  Children,  etc. 

EDITED    AND    ARRANGED    FOR   THE    PRESS 

BY  P.  H.  PYE-SMITH;  M.D.,  F.R.C.P., 

Lecturer  on  Medicine  in  Guy's  Hospital,  London,  etc. , 

WITH  A  SECTION  ON  CUTANEOUS  AFFECTIONS,  BY  THE  EDITOR,  A  CHAPTER  ON  CAR- 
DIAC DISEASES,  BY  SAMUEL  WlLKES,  M.  D.,  F.  R.  S.,  AND  TWO  INDEXES,  ONE  OF 
AUTHORS  AND  ONE  OF  SUBJECTS,  BY  ROBERT  EDMUND  CARRINGTON. 

Two  Volumes.  Royal  Octavo.  1900  Pages. 

Price  in  Cloth,  $8.00.     Pull  Leather,  $10.00.     Half  Morocco,  $12.00.    Half  Russia,  $12.00. 


It  is  based  on  laborious  researches  into  the  pathological  and  clinical  records  of 
Guy's  Hospital,  London,  during  the  twenty  years  in  which  the  author  has  held  office 
there  as  Medical  Registrar,  as  Pathologist,  and  as  Physician.  Familiar  beyond  most, 
if  not  all,  of  his  contemporaries,  with  modern  medical  literature,  a  diligent  reader  of* 
French  and  German  periodicals,  Dr.  Fagge,  with  his  remarkably  retentive  memory  and 
methodical  habits,  was  able  to  bring  to  his  work  of  collection  and  criticism  almost 
unequaled  opportunities  of  extensive  experience  in  the  wards  and  dead  house.  The 
result  is  that  which  will  probably  be  admitted  to  be  a  fuller,  more  original,  and  more 
elaborate  text-book  on  medicine  than  has  yet  appeared.  It  is  the  first  of  importance 
emanating  from  Guy's  Hospital,  and  the  only  two-volume  work  on  the  Practice  of 
Medicine  that  has  been  issued  for  a  number  of  years.  Several  subjects,  such  as 
Syphilis,  that  are  usually  omitted  or  but  slightly  spoken  of  in  a  general  work  of  this 
character,  receive  full  attention. 

Dr.  Walter  Moxon,  one  of  Dr.  Fagge's  contemporaries,  and  a  great  personal 
friend,  writes  of  him,  in  a  recent  number  of  the  London  Lancet : — 

"  Fagge  was,  to  my  mind,  the  type  of  true  medical  greatness.  I  believe  he  was  capable  of  any  kind  of 
excellence.  His  greatness  as  a  physician  became  evident  to  observers  of  character  very  soon  after  his  brilliant 
student  career  had  placed  him  on  the  staff  of  Guy's  Hospital;  he  did  not  merely  group  already  known  facts, 
but  he  found  new  facts.  Former  volumas  of  Guy's  Hospital  Reports  contain  ample  and  most  valuable  proof  of 
his  greatness  as  a  physician.  His  powe.  of  observation  was  sustained  by  immense  memory,  and  brought  into 
action  by  vivid  and  constant  suggestiveness  of  intelligence.  He  was  a  physician  by  grace  of  nature,  and  being 
gifted  with  a  quickness  of  perception,  a  genius  for  clinical  facts  and  a  patience  in  observation,  he  was  at  once 
recognized  as  a  successful  practitioner  and  a  leading  figure  in  the  hospital  and  among  the  profession. 


NEW  TEXT-BOOKS. 


Macalister's  Human  Anatomy.     816  Illustrations  (400  of 
which  are  Original).     Just  Ready. 

A  NEW  TEXT  BOOK  for  Students  and  Practitioners,  Systematic  and  Topographical, 
including  the  Embryology,  Histology  and  Morphology  of  Man.  With  special 
reference  to  the  requirements  of  Practical  Surgery  and  Medicine. 
By  ALEX.  MACALISTER,  M.D.,  F.R.S.,  F.S.A.,  Professor  of  Anatomy  in  the  Univer- 
sity of  Cambridge,  England;  Examiner  in  Zoology  and  Comparative  Anatomy, 
University  of  London;  formerly  Professor  of  Anatomy  and  Surgery,  University 
of  Dublin.  With  816  Illustrations,  400  of  which  are  original.  Octavo. 

Cloth,  $7.50;  Leather,  $8.50 

***  Professor  Macalister's  reputation  as  an  Anatomist  and  Zoologist  is  such  that 
nothing  need  be  said  of  the  scientific  value,  of  this  book.  Regarding  the  illustrations, 
printing  and  binding  we  may  say,  however,  that  the  workmanship  is  of  the  best 
character  in  every  respect.  No  expense  has  been  spared  to  make  a  handsome  vol- 
ume, the  400  original  illustrations  adding  greatly  to  its  appearance  as  well  as  to  its 
practical  value  as  a  working  book  for  students  and  physicians. 

Potter's  Materia  Medica,  Pharmacy  and  Therapeutics. 
Second  Edition.     Revised  and  Enlarged. 

A   HANDBOOK   OF   MATERIA    MEDICA,  PHARMACY   AND   THERAPEUTICS — including 

the  Physiological  Action  of  Drugs,  Special  Therapeutics  of  Diseases,  Official  and 
Extemporaneous  Pharmacy,  etc.  By  SAM'L  O.  L.  POTTER,  M.A.,  M.D.,  Professor 
of  the  Practice  of  Medicine  in  Cooper  Medical  College,  San  Francisco;  Late 
A.  A.  Surgeon,  U.  S.  Army,  Author  of  "  Speech  and  its  Defects,"  and  the  "Quiz- 
Compends"  of  Anatomy  and  Materia  Medica,  etc.  Revised,  Enlarged  and  Ini- 
oroved.  Octavo.  With  Thumb  Index  in  each  copy. 

Cloth," $4.00;  Leather,  $5.00 

"  The  author  has  aimed  to  embrace  in  a  single  volume  the  essentials  of  practical  materia 
medica  and  therapeutics,  and  has  produced  a  book  small  enough  for  easy  carriage  and  easy  ref- 
erence, large  enough  to  contain  a  carefully  digested,  but  full,  clear  and  well-arranged  mass  of 
information.  Pie  has  n  >t  adhered  to  any  pharmacopoeia,  as  is  the  case  of  certain  recent  manuals, 
thereby  limiting  his  woik,  and  in  this  day  of  new  remedies  causing  c  nstant  disappointment,  but 
has  brought  it  up  to  date  in  the  most  satisfactory  way.  No  new  remedy  of  any  acknowledged 
value  is  omitted  from  this  libt.  Under  each  the  section  on  physiological  action  and  therapeutics 
has  been  written  with  care.  ...  In  the  enumeration  of  drugs  suited  to  different  disorders  a 
very  successful  effort  at  discrimination  has  been  made,  both  in  the  stage  of  disease  and  in  the 
cases  peculiarly  suited  to  the  remedy.  It  is  no  mere  libt  of  ciseases  followed  by  a  catalogue 
of  drugs,  but  is  a  digest  of  modern  therapeutic--,  and  as  such  will  prove  of  immense  use  to  its 
possessor." — 7Vie  therapeutic  Gazette. 

Winckel's  Obstetrics.     Original  Illustrations. 

A  TEXT-BOOK   OF   OBSTETRICS,  INCLUDING   THE   PATHOLOGY   AND  THERAPEUTICS 

OF  THE  PUERPERAL  STATE.  By  DR.  F.  WiNCKEL,  Professor  of  Gynaecology, 
and  Director  of  the  Royal  University  Clinic  for  Women,  in  Munich.  Authorized 
Translation,  by  J.  CLIFTON  EDGAR,  M.D.,  Adjunct  Professor  to  the  Chair  of 
Obstetrics,  Medical  Dept,  University,  of  the  City  of  New  York,  with  nearly  200 
handsome  illustrations,  the  majority  of  which  are  original  with  this  work.  Octavo. 

Cloth,  $6.00;  Leather,'  $7.00 


PUBLISHED  ANNUALLY. 


1891. 


NOW  READY.     40™  YEAR. 


THE:  PHYSICIAN'S  VISITING  LIST. 


(LINDSAY  &  BLAKISTON'S.) 

CONTENTS. 


Ki-MANAC  for  1890  and  1891. 

TABLE  OF  SIGNS  to  be  used  in  keep'ng  accounts. 

MARSHALL  HALL'S  READY  METHOD  IN  ASPHYXIA. 

POISOMS  AND  ANTIDOTKS,  revised  for  1890. 

THE  METRIC  OR  FRENCH  DECIMAL  SYSTEM  OF 
WEIGHTS  AND  MEASURES. 

DOSE  TABLE,  revised  and  rewritten  for  1890,  by  Ho- 
BART  AMORY  HARE,  M.D  ,  Demonstrator  of  Thera- 
peutics, University  of  Pennsylvania. 

LIST  OF  NEW  REMEDIES  for  1890,  by  same  author. 

AIDS  TO  DIAGNOSIS  AND  TREATMENT  OF  DISEASES  OF 
THE  EYE,  DR.  L.  WEBSTER  Fox,  Clinical  Asst.  Eye 
Dept  ,  Jefferson  Medical  College  Hospital,  and  G. 
M.  GOULD,  M.D. 

DIAGRAM  SHOWING  ERUPTION  OF  MILK  TEETH,  DR. 
Louis  STARR,  Prof,  of  Diseases  of  Children,  Univer- 
sity Hospital,  Philadelphia. 


POSOLOGICAL  TABLE,  MEADOWS. 

DISINFECTANTS  AND  DISINFECTING. 

EXAMINATION  OF  URINE,  DR.  J.  DALAND,  based  upon 
Tyson's  "  Practical  Examination  of  Urine."  6th 
Edition. 

INCOMPATIBILITY,  DR.  S.  O.  L.  POTTER. 

A  NEW  COMPLETE  TABLE  FOR  CALCULATING  THE 
PERIOD  OF  UTERO-GESTATION. 

SYLVESTER'S  METHOD  FOR  ARTIFICIAL  RESPIRATION. 
Illustrated. 

DIAGRAM  OF  THE  CHEST. 

BLANK  LEAVES,  suitably  ruled,  for  Visiting  Lists, 
Monthly  Memoranda,  Addresses  of  Patients  and 
others  ;  Addresses  of  Nurses,  their  references,  etc. ; 
Accounts  asked  for;  Memoranda  of  Wants  ;  Obstet- 
ric and  Vaccination  Engagements;  Record  of  Births 
and  Deaths  ;  Cash  Account,  etc. 


For  25  Patients  weekly. 
50 

75        "  " 

TOO        "  " 

50  "  "  2  Vols. 

loo        "  "          2  Vols. 


REGULAR   EDITION. 

Tucks,  pockets  and  Pencil,  $1.00 


an.  to  June 
uly  to  Dec. 
an.  to  June 
uly  to  Dec. 


For  25  Patients  weekly. 
50        " 

50        "  "          2  Vols. 


INTERLEAVED  EDITION. 

Interleaved,  tucks  and  Pencil, 


j  Jan.  to 
(  July  to 


1.50 

2.00 
2.50 

3-00 


1.25 
1.50 

3-00 


PERPETUAL  EDITION,  without  Dates. 
No.  1.     Containing  space  for  over  1300  names,  with  blank  page  opposite  each 

Visiting  List  page.  Bound  in  Red  Leather  cover,  with  pocket  and  Pencil,  $1.25 
No.  2.  Containing  space  for  2600  names,  with  blank  page  opposite  each 

Visiting  List  page.     Bound  like  No.  I,  with  Pocket  and  Pencil,     .     .     .     .    1.50 

MONTHLY  EDITION,  without  Dates. 

No.  1.     Bound  without  Flap  or  Pencil, 75 

No.  2,        "      with  Tucks,  Pencil,  etc i.oo 

These  lists,  without  dates,  can  be  commenced  at  any  time,  and  used  until  full, 
and  are  particularly  useful  to  young  physicians  unable  to  estimate  the  number  of 
patients  they  may  have  during  the  first  years  of  Practice,  and  to  physicians  in  locali- 
ties where  epidemics  occur  frequently.  In  the  Monthly  Edition  the  patient's  name 
has  to  be  entered  but  once  each  month. 

"  For  completeness,  compactness,  and  simplicity  of  arrangement  it  is  excelled  by  none  in  the  market."—^.  ? 
Medical  Record. 

"The  book  is  convenient  in  form,  not  too  bulky,  and  in  every  respect  the  very  best  Visiting  List  published.' 
—  Canada  Medical  and  Surgical  Journal, 

"  After  all  the  trials  made,  there  are  none  superior  to  it."—Gaillard's  Medical  Journal. 
The  most  popular  Visiting  List  extant."— Buffalo  Medical  and  Surgical  Journal. 

"  We  have  used  it  for  years,  and  do  not  hesitate  to  pronounce  it  equal,  if  not  superior,  to  any."—  Southern 
Clinic, 

This  is  not  a  complicated  system  of  keeping  accounts,  but  a  plain,  systematic 
record  which,  with  the  least  expenditure  of  time  and  trouble,  keeps  an  accurate  and 
concise  list  of  daily  visits,  engagements,  etc. 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 


JUL   9       ** 


30m-l,'15 


331983 


I 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


